2016 Anomalous Absorption Abstract Booklet - Meetings

Transcription

46th Annual Anomalous Absorption Conference
Old Saybrook, CT
May 1-6, 2016
J. S. Ross, G. Swadling, M. D. Rosen, K. Widmann, B. Heeter, J. Moody
Lawrence Livermore National Laboratory
7000 East Ave.
Livermore, CA 94550
[email protected]
An experimental campaign was completed at the Omega laser facility to characterize the
blow-off plasma from Au sphere targets using Thomson scattering. The experiments are
designed to be a 1D experimental configuration that captures the essential radiation and
transport physics of NIF lasers interacting with a Au hohlraum at laser intensities ranging
from 1x1014 to 1x1015 W/cm2. The time-dependent plasma conditions (Te ~1.8 keV, ne
~1x1020 cm-3, and Z ~45) are measured using Thomson scattering for a range of radial
locations and the x-ray flux time-history is characterized using Dante. The experimental
data is compared to 1D radiation-hydrodynamic models using several different models
for the heat flux and atomic physics. Various flux limiters with approximate atomic
physics models are unable to reproduce the measured plasma conditions. The
simulations show improved agreement with measurements when a “two-streaminstability” flux limit model, augmented by an ad-hoc anomalous absorption (presumably
due to the same ion acoustic turbulence that leads to the flux limitation) near the critical
surface, is considered. An additional set of experiments has been completed where the
Au sphere was located at the center of a CH filled gas-bag. This configuration mimics a
gas-filled hohlraum and is used to evaluate gas-wall mix and wall motion.
*This work was performed under the auspices of the U.S. Department of Energy by
Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
1
Monday
Thomson scattering characterization of a 1D Hohlraum
wall surrogate (a Au sphere) for improved
understanding of hohlraum physics*
M1-1
M1-2
Old Saybrook, CT
May 1-6, 2016
Measurements of the effect of adiabat on the shell
thickness of direct-drive implosions on OMEGA*
D. T. Michel, S. X. Hu, A. K. Davis, V. N. Goncharov, I. V. Igumenshchev, R. S.
Craxton, P. B. Radha, and D. H. Froula
Laboratory for Laser Energetics, University of Rochester
250 East River Road, Rochester, NY 14623-1299
[email protected]
Imaging the soft x rays emitted by both the coronal plasma and the hot spot of a directly
driven imploding CH target on the OMEGA Laser System was used to measure the
thickness of the shell at the beginning of the target deceleration for various shell adiabats.
The soft x rays emitted by the coronal plasma were used to determine the position of the
ablation front, while the emission of the hot spot was used to determine the position of
the inner surface of the shell. The adiabat of the shell was varied between 1.8 and 6 by
changing the intensity of a small picket before the main drive of the laser pulse.
Decreasing the adiabat of the shell from 6 to 2.5, the measured shell thickness decreases
from 75 µm to 60 µm. This decrease is consistent with simulations that neglect imprint
(75 µm to 40 µm). When further decreasing the shell’s adiabat (2.5 to 1.8), an increase of
the shell thickness (60 µm to 75 µm) was observed while the shell thickness was
calculated in simulations that neglect imprint to continue to be reduced. When including
laser imprint in the simulations, the measured thicknesses of the shell were reproduced.
These results highlight the importance of choosing the optimum adiabat to mitigate shell
nonuniformities and improve the implosion performances in direct-drive inertial
confinement fusion.
*This material is based upon work supported by the Department of Energy National
Nuclear Security Administration under Award Number DE-NA0001944, the University
of Rochester, and the New York State Energy Research and Development Authority. The
support of DOE does not constitute an endorsement by DOE of the views expressed in
this article.
2
Old Saybrook, CT
May 1-6, 2016
Low convergence path to fusion ignition*
Kim Molvig, Mark J. Schmitt and Gene H. McCall
Los Alamos National Laboratory
MS F699
Los Alamos, NM 87544
[email protected]
A new class of inertial fusion ignition capsules is presented that consists of a nested
series of concentric metal shells focused to a gold pusher shell filled with deuterium-tritium
fuel. These Revolver class† capsules are designed to achieve robust thermonuclear ignition
conditions "upstream" in the fuel with minimal pusher shell deceleration, minimizing
Rayleigh-Taylor mix and maximizing burn fraction. The intent is to provide a simple class
of target designs capable of producing multi-mega joule yields from DT fuel masses of 10s
of μg, absorbed drive energies less than 2 MJ, and burn fractions exceeding 50% for yields
in excess of 4 MJ. High gain is not a consideration. The class has a number of distinguishing
features:
1. Capsule material is predominantly metal, of order 99% by mass
2. Descending shell mass ratios ∼ 1/6 for velocity multiplication
3. Fuel convergence C∼10 and implosion velocity u < 20 cm/μs
4. Reciprocal relationship u ∝ C⁻¹ (contrasts to existing ignition designs that require
both to be large)
Revolver targets require investing energy in the heavy metal shells, although this investment
appears to be well within the capabilities of the NIF laser in direct drive††. In fact, as the
companion paper shows††, laser requirements to drive the third ablator shell are well
satisfied by the NIF laser in direct drive. The relatively low ablation pressure achievable
with direct drive (at most 100 Mbar) is not an issue for the Revolver capsules while being a
significant problem for existing designs.
A simplified physics model of the targets has been developed that relates all the
target specifications to a single parameter (usually taken to be either fuel mass or drive
energy) with analytic formulas that can be computed in a spread sheet. Thus fuel mass
determines drive energy and all geometric specifications. Basic performance metrics such as
convergence, implosion velocity, and ignition margin are predicted by the model and agree
well with complete burn code simulations. The burn fraction of 50% is verified as well.
Issues remaining are: fabrication of the triple shell targets, laser configuration and
symmetry requirements for both drive and shell configurations are unknown. Improved
performance compared to existing designs with respect to hydro instabilities should be
established with forthcoming multi-dimensional simulations.
†
Kim Molvig, Mark J. Schmitt, B.J. Albright, E.S. Dodd, N.M. Hoffman, G.H. McCall, and
S.D. Ramsey, LA-UR-16-20796 (submitted to Phys. Rev. Lett.)
††
Mark J. Schmitt , Kim Molvig and Gene H. McCall, this conference.
* This research supported by the US DOE/NNSA, performed in part at LANL, operated by
LANS LLC under contract DE-AC52-06NA25396.
3
M1-3
M1-4
Old Saybrook, CT
May 1-6, 2016
Design of a low convergence fusion ignition capsule*
Mark J. Schmitt, Kim Molvig and Gene H. McCall
MS F699
[email protected]
Design of a Revolver class† inertial fusion ignition capsule is presented that consists of a
directly-driven pure Be ablator shell generating the pressure drive for two subsequent
heavy metal inner shells, centered on a small volume of liquid deuterium-tritium (DT)
fuel (10s of μg). The capsule achieves robust thermonuclear ignition conditions before
significant pusher shell deceleration to obviate deceleration Rayleigh-Taylor (RT) mix
and maximize burn fraction. The Revolver triple-shell design is well matched to direct
drive conditions achievable on the NIF. Advantages over conventional ignition designs
include low drive intensities (~2x1014 W/cm2) that mitigate LPI/CBET and keep ablative
RT small, an absence of non-local heat conduction, slow implosion velocities (v ~ 20
cm/μs), a modest fuel convergence of 9 and a DT burn fraction of ~50%. Moreover, the
required driver/pusher shell convergence ratios are low (~3) minimizing hydrodynamic
instability growth during the implosion and eliminating the need for laser zooming of the
~8ns laser pulse. Design performance is tolerant to preheat, substantial variations in
radial shell placement, shell thickness, inter-shell gas density and laser pulse profile.
†
Kim Molvig, M.J. Schmitt, B.J. Albright, E.S. Dodd, N.M. Hoffman, G.H. McCall, and
S.D. Ramsey, LA-UR-16-20796, submitted to Phys Rev Lett.
* This research supported by the US DOE/NNSA, performed in part at LANL, operated
by LANS LLC under contract DE-AC52-06NA25396.
4
M1-5
5
Old Saybrook, CT
May 1-6, 2016
M2-1
BigFoot: Formation of a high areal density hotspot
at the National Ignition Facility*
C. A. Thomas, K. L. Baker, S. F. Khan, D. T. Casey, D. C. Eder, D. H. Munro,
R. C. Nora, and B. K. Spears
7000 East Avenue
Livermore CA 94550
[email protected]
The conventional approach to inertial confinement fusion (ICF) is to maximize areal
density at stagnation (1.6-2 g/cm2) to maximize gain. At NIF-scale, this requires careful
pulse shaping, and success in a trade against capsule stability, hohlraum physics, and
gross energetics. For burn to be initiated, the hotspot must be 4-5 keV in temperature,
with sufficient areal density to self-heat (0.1-0.2 g/cm2).
An alternate approach to inertial confinement fusion would be to assemble an ignitionrelevant hotspot first, and increase total areal density second. To reduce convergence and
increase stability, we use precision shock timing to increase the average adiabat of DT 1,
and maximize robustness by adding entropy to the inside of the fuel. In concept, the goal
is a hotspot > 6 keV, ρR > 0.3 g/cm2, that is part of an incremental plan for areal density
and gain if hotspot ignition is achieved.
Success will require a hohlraum that is tunable, azimuthally symmetric, and capable of
high velocity (450-500 um/ns). To this end, we introduce a 0.3 mg/cm3 gas-fill hohlraum
with a 6 ns pulse appropriate to high-density carbon ablators 2,3. Hohlraum efficiency and
scalability is optimized by quad-splitting the outer beams 4, and aided by modifications to
the target.
We report on experimental findings using this approach and platform, and on future
optimizations that could allow greater laser power, energy, shape control, and capsule
stability.
*Work performed under the auspices of the U.S. Department of Energy by Lawrence
Livermore National Laboratory under Contract DE-AC52-07NA27344.
1
Goncharov et al., “Improving the hot-spot pressure and demonstrating ignition hydrodynamic
equivalence in cryogenic deuterium-tritium implosions on OMEGA”, Phys. Plasmas 21, 056315, 2014.
2
D. D. Ho et al., APS-DPP, invited presentation, Orlando (2007).
3
L. F. Berzak Hopkins et al., Phys. Plasmas 22, 056318 (2015).
4
R. L. Berger et al., this conference.
6
Old Saybrook, CT
May 1-6, 2016
Integrated simulations and predictive capability for
near-vacuum hohlraums in the NIF Marble platform*
R. E. Olson, T. J. Murphy, M. R. Douglas, J. R. Fincke, B. M. Haines,
J. A. Oertel, R. C. Shah, and J. M. Smidt
[email protected]
Experiments are underway to develop the NIF Marble platform, which will be used to
quantify the influence of heterogeneous mix on fusion burn1-3. This platform utilizes a
plastic (CH) capsule filled with a deuterated plastic foam (CD) with a density of a few
tens of milligrams per cubic centimeter, with tritium gas filling the voids in the foam. The
capsule is driven by x-rays generated in a NIF near-vacuum hohlraum (NVH)4.5. About a
half-dozen preliminary NIF Marble experiments have been performed to date. In these
experiments, good predictive capability has been demonstrated for the hohlraum x-ray
drive, the implosion bang time, and the hot spot size and symmetry behavior in terms of
time-resolved P0 and P2/P0. Since the Marble platform employs a NVH, the timedependent symmetry of the implosion can be controlled via dynamic beam phasing6. Due
to low ablator mass and modest capsule convergence, the preliminary Marble
experiments have demonstrated the ability to employ dynamic beam phasing and obtain
good predictive capability of time-resolved hot spot symmetry without recourse to the use
of an “enhanced propagation” model6 or multipliers on the laser power. Although our hot
spot is quite round at the time of peak x-ray emission, design of the current, preliminary
Marble laser pulse shape has been constrained by a combination of obtainable foam
deuteration levels and NIF optics damage restrictions. This has resulted in a predicted
(and observed) symmetry swing during the capsule implosion. Going forward, increased
foam deuteration levels will allow for a significant reduction in symmetry swing while
producing adequate TN yield and remaining within the low optics damage constraints.
*This work was performed at LANL, operated by LANS, LLC for the U.S. DoE under Contract No. DEAC52-06NA25396.
T. J. Murphy, M. R. Douglas, et al., “Progress in the development of the MARBLE platform for studying
thermonuclear burn in the presence of heterogeneous mix on OMEGA and the National Ignition Facility,”
to be published Journal of Physics Conf. Ser. (2016).
2
M. R. Douglas et al., “Overview of the Marble experiment,” Bull. Am. Phys. Soc. 59, 112 (2014).
3
T. J. Murphy, M. R. Douglas, et al., “Results from and plans for the development of the MARBLE
platform for studying thermonuclear burn in the presence of mix on OMEGA and the National Ignition
Facility,” Bull. Am. Phys. Soc. 60, 323 (2015).
4
S. Le Pape et al., “Observation of a reflected shock in an indirectly driven spherical implosion at the
National Ignition Facility,” Phys. Rev. Lett. 112, 225002 (2014).
5
L. F. Berzak Hopkins, et al., “First high-convergence cryogenic implosion in a near-vacuum hohlraum,”
Phys. Rev. Lett. 114, 175001 (2015).
6
L. F. Berzak Hopkins et al., “Near-vacuum hohlraums for driving fusion implosions with high density
carbon ablators,” Phys. Plasmas 22, 056318 (2015).
1
7
M2-2
M2-3
Old Saybrook, CT
May 1-6, 2016
Use of hohlraum liners to improve the hohlraum
performance
K. L. Baker, C. A, Thomas, T. Baumann, R.L. Berger, M. Biener, D. Callahan, D. Casey,
P.M. Celliers, F. Elsner, S. Felker, A.V. Hamza, D. Hinkel, H. Huang, O. S. Jones, O.L.
Landen, J. L. Milovich, A. S. Moore, J. D. Moody, A. Nikroo, R. Olson, B. Spears and D.
Strozzi
7000 East Ave., L-481
Livermore, Ca 94550
[email protected]
Hohlraum liners can be used to improve the performance of many aspects in hohlraum
physics. They can be used to modify the x-ray spectrum where the laser spots interact
with the hohlraum wall, thereby reducing the symmetry swings induced by m-band
driven primarily from the outer beam spots. A modified x-ray spectrum can reduce or
possibly eliminate the need for dopant in ICF capsules which in turn reduces the ablation
front growth factors leading to a more stable implosion. They can be used to introduce
low Z species into the wall to alter the gain of laser plasma interactions. At the lowest
densities they can be used to eliminate two plasmon decay and greatly reduce wall
motion. Diminished wall motion would reduce symmetry swings and potentially allow
some ICF platforms to operate at lower gas fill densities where additional problems
arising from parametric instabilities and cross beam energy transfer could be avoided. All
of these are beneficial to the performance of the hohlraum. In this presentation
experimental results from three separate liner experiments that have been conducted on
the NIF, including copper, ZnO and Ta2O5 liners, will be presented.
* This work was performed under the auspices of the U.S. Department of Energy by
LLNL under Contract DE-AC52-07NA27344.
8
Old Saybrook, CT
May 1-6, 2016
2 shock implosions at NIF*
G. Kyrala, J. Kline, T. Ma†, S. Khan†, S. MacLaren†, J. D. Salmonson†, J. Pino†,
T. Dittrich†, J. Ralph†, D. P. Turnbull†, P. Celliers†, R. Rygg†, and P. Kervin†
P.O. Box 1663
[email protected]
†
Livermore, CA 94551
Two shock indirect drive implosions have been designed and performed at the National
Ignition Facility to produce symmetric 1D like implosions. This platform will be used to
study departure of the implosions from 1D due to different imposed perturbations. In this
work we will review some of the work and concentrate on the effect of implosion
convergence on the measured properties, such as symmetry, ion temperature and nuclear
yields. The measured effects of laser pulse shapes on the LPI will be presented as well.
*This work was performed at Los Alamos and Lawrence Livermore National
Laboratories, funded by the US Department of Energy.
9
M2-4
M2-5
10
M3-1
11
Poster Session
PM-1
Old Saybrook, CT
May 1-6, 2016
A wave-based model for cross-beam energy transfer
in inhomogeneous plasmas*
J. F. Myatt, J. G. Shaw, D. H. Edgell, R. Follett, V. N. Goncharov, A. V. Maximov,
R. W. Short, W. Seka, and D. H. Froula
[email protected]
Power transfer between crossing laser beams in plasma [cross-beam energy transfer
(CBET)] has shown itself to be of fundamental importance to both direct- and indirectdrive inertial confinement fusion. 1 In direct drive, the effect has been modeled in
radiation–hydrodynamics codes by exchanging energy between crossing rays in the raytrace algorithm used for laser-energy deposition. The exchange is computed according to
the locally computed stimulated Brillouin scattering gain rate that is based on an
extension of the work by Randall. 2 The correct treatment of this power exchange in the
presence of inhomogeneity, including beam-turning points, caustics, laser coherence
(speckle), and laser polarization, is not prescribed in this model. To address the
importance of these effects, a new 3-D wave-based model of CBET has been developed
that directly solves Maxwell’s equations in an inhomogeneous plasma with flow coupled
to a linearized ion-acoustic response. The first results will be presented.
this article.
1
I. V. Igumenshchev et al., Phys. Plasmas 17, 122708 (2010); P. Michel et al., Phys. Rev. Lett. 102,
025004 (2009).
2
C. J. Randall, J. R. Albritton, and J. J. Thomson, Phys. Fluids 24, 1474 (1981).
12
Old Saybrook, CT
May 1-6, 2016
The effect of cross-beam energy transfer on twoplasmon decay in direct-drive implosions*
D. H. Froula, R. K. Follett, R. J. Henchen, A. K. Davis, V. N. Goncharov, D. H. Edgell,
A. A. Solodov, D. T. Michel, J. F. Myatt, J. G. Shaw, and C. Stoeckl
[email protected]
Mitigation of cross-beam energy transfer (CBET) in direct-drive implosions was shown
to increase the hot electrons generated by two-plasmon decay. Reducing the diameter of
the laser spots by 30% significantly reduces CBET and the laser absorption was
measured to increase from 75% to nearly 90% (Ref. 1). The reduced CBET leads to
higher intensity at the quarter-critical density surface, increasing the hot-electron
production by a factor of ~7. Adding a thin layer (0.6 to 1.1 µm) of Si to the target ablator
reduced the hot-electron fraction by a factor of ~2. Spatially resolved Thomson-scattering
measurements show an ~15% increase in the electron temperature and an increase in the
Si fraction at the quarter-critical surface when the Si layer is added. Three-dimensional
laser–plasma interaction simulations of hot-electron production using the code LPSE
show that in addition to the reduced gain (smaller ILn / Te), the observed reduction in hot
electrons results from increased electron–ion collision frequencies and reduced Landau
damping of ion-acoustic waves.
this article.
1
D. H. Froula et al., Phys. Rev. Lett. 108, 125003 (2012).
13
PM-2
PM-3
Old Saybrook, CT
May 1-6, 2016
Overview of first CBET Campaign at the Nike Laser*
J. L. Weaver, P. McKenty†, J. Oh, D. Kehne, S. Obenschain, R. H. Lehmberg‡, F. Tsung§,
A. J. Schmitt, and V. Serlin
Plasma Physics Division, U.S. Naval Research Laboratory
4555 Overlook Ave. SW
Washington, DC 20375
[email protected]
†
Rochester, NY 14623
‡
Research Support Instruments
Lanham, MD 20706
§
University of California, Los Angeles
Los Angeles, CA 90095
An initial cross-beam energy transport (CBET) campaign at the Nike krypton-fluoride (KrF)
laser of NRL was recently completed. The experimental series utilized both of Nike’s two
widely separated (135o in azimuth) beam arrays to simultaneously irradiate solid targets. This
laser facility has several characteristics that provide a unique platform for CBET work including short wavelength (248 nm), large bandwidth (1-3 THz), beam smoothing by
induced spatial incoherence (ISI), and full aperture focal spot zooming. Various target types
were explored: planar polystyrene slabs, hollow cylindrical polyimide tubes, and solid
polystyrene spheres. Operation at intensities up to ~7x1014 W/cm2 incorporated etalons in the
front end to shift the central wavelength of the output laser spectrum of the main beam array
over a range of +/- ~0.2 nm. Scattered light diagnostics included time-integrated and timeresolved spectrometers to monitor backscattered light and laser light traveling around the
target. This presentation will provide a summary of the experimental data and discuss CBET
modeling with the DRACO code at LLE.
*Work supported by DoE/NNSA.
14
PM-4
46thAnnualAnomalousAbsorptionConference
OldSaybrook,CT
May1-6,2016
Towardsamoreprecisedrivingofcapsulesinignition-scalehohlraums*
WilliamL.KruerândCliffA,Thomas
LawrenceLivermoreNationalLaboratory
7000EastAvenue
Livermore,CA94550
[email protected]
1
PrecisionNovaexperiments demonstratedtheimportanceofratherprecisely
irradiatingtheinteriorwallsofahohlraum,evenforimplodingcapsulestoa
convergenceratioof~20.Precisionimplosionsinagas-filledignition-scale
hohlraumtoevenhigherconvergencerequireanimprovedunderstandingofboth
theplasmaconditionsandthelaserenergydepositionintimeandspace.The
plasmaconditionsaresensitivetoheattransportinhibition,whichhasbeena
recurrentthemeinexperimentswithearlierlasers.Suchinhibitionhasbeen
proposed2inordertobettermodelNIFgas-filledhohlraums.Animprovedselfconsistentmodelforthecommonlyinvokedinhibitionbytwo-streamturbulenceis
outlined,andsomesimpleestimatesmade.Theseestimatessuggestthatthe
postulatedreductioninheattransportmayactuallybeduetootherprocesses,such
asself-generatedmagneticfields.SeveralwaystoreducesuchBfieldeffectsare
discussed,includinggreatertemporalsmoothingofspecklestructureinthelaser
beamsandreductionofhotspotsdrivenintolaserbeamsbyCBET.Finallyan
importantdiagnosticchallengeistomeasuretheangulardistributionofstimulated
scatteringwithinthehohlraum.
^consultant
1.JohnD.Lindl,et.al.,Phys.Plasmas11,339(2004)
2.CliffA.Thomas(privatecommunication)
*ThisworkwasperformedundertheauspicesoftheU.S.DepartmentofEnergyby
LawrenceLivermoreNationalLaboratoryunderContractDE-AC52-07NA27344.
15
PM-5
Old Saybrook, CT
May 1-6, 2016
Controlling laser plasma interactions with temporal
bandwidth*
F. S. Tsung, R. Lehmberg†, and J. Weaver†
UCLA
405 Hilgard Ave.
[email protected]
†
Naval Research Laboratory
We are performing particle-in-cell simulations using the code OSIRIS to study the effects
of laser plasma interactions in the presence of temporal bandwidth under conditions
relevant to current and future experiments on the NIKE laser. Our simulations show that,
for sufficiently large bandwidth, the saturation level, and the distribution of hot electrons,
can be effected by the addition of temporal bandwidths (which can be accomplished in
experiments using beam smoothing techniques such as ISI). In our early simulations, the
frequency bandwidth is obtained through a series of pulses. We have performed
additional simulations to address the effects random phases have on the control of LPI’s
under identical plasma conditions. We will also discuss the effects of spatial smoothing
with our next round of simulations.
*This work conducted under the auspices or NRL.
16
Old Saybrook, CT
May 1-6, 2016
Laser plasma instability (LPI) experiments with plasma
profile measurements at the Nike laser*
Jaechul Oh, J. L. Weaver, V. Serlin, and S. P. Obenschain
Plasma Physics Division
U.S. Naval Research Laboratory
4555 Overlook Avenue SW
[email protected]
With short wavelength (248 nm), large bandwidth (1-3 THz) and uniform beam
smoothing, kripton-flouride (KrF) lasers offer advantages for direct drive inertial
confinement fusion, such as the higher ablation pressure via efficient collisional light
absorption and the higher maximum usable laser intensity by increasing LPI threshold
intensities. Previous LPI experiments1 with the Nike KrF laser observed two plasmon
decay (TPD) signatures near quarter critical density (nc/4) in CH plasmas at laser
intensities above ~1x1015 W/cm2. Further understanding of the LPI processes requires
detailed knowledge of the electron density (ne) and temperature (Te) profiles in plasma,
but their measurements were absent in the previous experiments. We performed the
present LPI experiment with the newly implemented grid imaging refractometer (GIR)2,
measuring the plasma profiles in the underdense coronal region up to ne ~ 4x1021 cm-3,
i.e., 0.23nc for 248 nm or 0.45nc for 351 nm light. The primary diagnostics for the LPI
measurements were time-resolved spectrometers with absolute intensity calibration in
spectral ranges relevant to the stimulated Raman scattering (SRS) and TPD. The observed
LPI behaviors will be presented and discussed with the measured data sets.
*Work supported by DoE/NNSA.
1
J. L. Weaver, J. Oh, L. Phillips, B. Afeyan, J. Seely, D. Kehne, C. M. Brown, S. P. Obenschain, V. Serlin,
A. J. Schmitt, U. Felman, R. H. Lehmberg, E. Mclean, and C. Manka, “Observation of parametric instabilities in the quarter critical density region driven by the Nike KrF laser,” Phys. Plasmas 20, 022701 (2013).
2
Jaechul Oh, J. L. Weaver, M. Karasik, and L. Y. Chan, “Measurements of electron density and temperature profiles in plasma produced by Nike KrF laser for laser plasma instability research,” Rev. Sci. Instr. 86, 083501 (2015).
17
PM-6
PM-7
Old Saybrook, CT
May 1-6, 2016
When gold and diamond meet at high velocity:
Collision, Diffusion, penetration?*
L. Divol, S. Le Pape, A. J. Kemp, J. S. Ross, R. L. Berger, S. Wilks, P. Amendt, L.
Berzak Hopkins, G. Huser†, J. Moody, A. J. Mackinnon‡, and N. Meezan
Street address
Livermore, CA zipcode
[email protected]
†
CEA, DAM
Arpajon, France
‡
SLAC National Accelerator Laboratory
Menlo Park, CA 94025
The Near Vacuum Campaign on the National Ignition Facility has sparked an interest on
the nature of the gold/carbon interface in low-density fill hohlraums at high velocity
(400 km/s), high electron temperature (>1 keV), low-electron density (1e21).
Experimental data suggests that the NIF inner beams are freely propagating to the waist
of the hohlraum when the simulations predict that a density ridge at the gold/carbon
interface blocks the inner beams. The discrepancy between experimental data and
simulation might be partly explained by the break-down of the fluid description of the
plasma interface. To test our assumption that a kinetic description is more appropriate in
this regime, we went to the Omega laser facility to study gold/carbon collision in the
relevant regime. We will present results comparing the plasma interface of a C/C, Al/C
and Au/C under the same laser drive in a cylindrical geometry. Time resolved images of
the self-emission of the interface as well as Thomson scattering data will be presented.
Comparison will be made with HYDRA fluid simulations and full collisional PIC (in a
simplified geometry). We will further discuss the role of a gas fill (He) and electron heat
conduction.
*This work conducted under the auspices of the U.S. Department of Energy by Lawrence
Livermore National Laboratory under Contract DE‐AC52‐07NA27344.
18
Old Saybrook, CT
May 1-6, 2016
Conduction-Zone Measurements Using X-Ray
Self-Emission Images*
A. K. Davis, D. T. Michel, R. Epstein, S. X. Hu, J. P. Knauer, and D. H. Froula
[email protected]
Time-gated soft x-ray self-emission images of directly driven targets were used to
measure the hydrodynamic conditions between the critical density surface and the
ablation front of a target (conduction zone) at the beginning of a laser pulse. These
images were absolutely calibrated using Dante, azimuthally averaged to reduce the noise,
and Abel-inverted to determine the emissivity at each point in the plasma. The electron
temperature was determined by varying the filter on the images to obtain the coarse
emission spectrum at each point. With the temperature determined, the density profile in
the corona could be determined from the emissivity profile. This measurement is critical
for inertial confinement fusion since it governs the length of time before the plasma is
large enough to provide substantial beam smoothing through thermal conduction,
determining the laser imprint efficiency. This region has previously proven challenging to
probe because the density is too high for optical diagnostics and the temperature is too
high for x-ray radiography.
this article.
19
PM-8
20
Old Saybrook, CT
May 1-6, 2016
T1-1
Crossed Beam Energy Transfer: assessment of the
Paraxial Complex Geometrical Optics approach versus
a time-dependent paraxial method*
Laser-Plasma Interaction (LPI) is subject to numerous nonlinear couplings between the
electromagnetic (EM) and the plasma waves. Among these couplings, the overlap of
several laser waves in the plasma produces ponderomotive beatings able to drive Ion
Acoustic Waves (IAWs), the latter being capable of leading to an energy exchange
between the incident laser waves. This process of Cross-Beam Energy Transfer (CBET)
occurs on a wide range of spatial and temporal scales. However, typical plasmas in the
ICF-related experiments have millimeter length scales and evolve on the nanosecond
time scale. Thus, an efficient modeling of the CBET must be added to radiative
hydrodynamics codes in order to design LPI experiments and to improve our
understanding of the laser-plasma coupling.
We present the modeling of the Crossed Beam Energy Transfer (CBET) using two
approaches: (i) the time-independent Paraxial Complex Geometrical Optics (PCGO) for
stochastically distributed Gaussian-shaped beamlets, and (ii) the time-dependent
conventional paraxial propagation of smoothed laser beams. Each description of the laser
propagation is coupled to a hydrodynamics code. Both approaches are compared in a
well-defined plasma configuration with density- and velocity- profiles corresponding to
inhomogeneous plasma, including a resonance zone in which the matching conditions for
a resonant coupling between the two laser beams are fulfilled. The comparison is made
for laser beams smoothed by random phase plates (RPP) and for `regular beams' without
speckles. In general, a good agreement is found between the PCGO simulations and the
fully time-dependent paraxial-type simulations, past a transient period on the picosecond
time scale. Based on these comparisons, performed for interaction parameters up to
2.1014 W.cm-2.µm2, the PCGO approach proves to be a reliable method to be
implemented in the hydrodynamics codes to describe the CBET in mm-scale plasmas.
*This work has been carried out within the framework of the EUROfusion Consortium
and has received funding from the Euratom research and training programme 2014-2018
under grant agreement No 633053. The views and opinions expressed herein do not
necessarily reflect those of the European Commission. This work has been partially
supported by the Agence Nationale de Recherche, project title `Ìlphygerie'' no. ANR-12BS04-0006.
21
Tuesday
Presenter A. Colaïtis1, S. Hüller2, D. Pesme2, G. Duchateau1 and V. Tikhonchuk1
1
Centre Lasers Intenses et Applications (CELIA), Université de Bordeaux/CNRS/CEA
33405 Talence, France
[email protected]
2
Centre de Physique Théorique, Ecole Polytechnique, CNRS, Université Paris-Saclay,
91128 Palaiseau, France
Old Saybrook, CT
May 1-6, 2016
T1-2
Inline Modeling of Cross-Beam Energy Transfer and
Raman Scattering in NIF Hohlraums*
D. J. Strozzi, S. M. Sepke, D. S. Bailey, P. Michel, L. Divol, G. D. Kerbel, C. A. Thomas
7000 East Ave.
Livermore, CA 94550
[email protected]
Self-consistent or “inline” models of cross-beam energy transfer (CBET) and stimulated
Raman scattering (SRS) have been added to the LLNL radiation-hydrodynamics codes
Hydra and Lasnex. They solve coupled-mode equations in the strong damping limit for
the laser and Raman intensities along refracted ray paths. This includes energy and
momentum deposition into driven plasma waves – ion acoustic waves for CBET and
Langmuir waves for SRS – and inverse bremsstrahlung (IB) absorption of SRS light.
A major motivation is to understand NIF hohlraum experiments with high gas fill, e.g.
“low-foot” and “high-foot” campaigns. These have large inner-beam SRS and use
substantial transfer to the inners for round implosions. Traditional modeling calculates
CBET by post-processing a rad-hydro run, and re-running with CBET applied to - and
backscatter removed from - the incident laser. For high-energy shots, this gives near
complete outer-beam depletion by CBET, and implosions that are much more prolate
than measured. One can match data by clamping the ion wave amplitude to ne/ne <
several 10-4: well below when nonlinearity is expected to reduce CBET (ne/ne ~ 0.01).
Inline CBET modeling with SRS removed from the incident laser (using Hydra) gives
less transfer to the inner beams than the traditional process during the early-time “picket.”
During peak laser power, the inline and traditional process give similar CBET to the
inners, and too prolate an implosion. Ion-wave deposition does not appear to
significantly reduce CBET1.
Inline CBET and SRS modeling (using Lasnex) show a significant effect on hohlraum
conditions, CBET, and implosion shape. The SRS light grows continuously from a seed
point in the hohlraum as it propagates out, with little IB absorption. SRS-driven
Langmuir waves remove significant inner-beam energy, and are mostly driven just inside
the laser entrance hole. The heating increases the entrance hole temperature and reduces
CBET somewhat. The heat conducts to the wall and produces polar, rather than
equatorial, x-ray flux. The net effect is outer beams that are not fully depleted, and a less
prolate implosion.1
* Work performed under the auspices of the U.S. Department of Energy by Lawrence
Livermore National Laboratory under Contract DE-AC52-07NA27344.
1
P. Michel et al., Phys. Rev. Lett. 109, 195044 (2012).
22
Old Saybrook, CT
May 1-6, 2016
Polarization dependence of cross-beam energy transfer
in unabsorbed light beamlets*
D. H. Edgell, J. Katz, J. F. Myatt, W. Seka, and D. H. Froula
[email protected]
A new diagnostic has been fielded on OMEGA to diagnose cross-beam energy transfer
(CBET) during implosions. Unabsorbed light from each OMEGA laser beam is imaged
as a distinct “spot” in time-integrated images. Each spot is, in essence, the end point of a
beamlet of light that originates from a specific region of a beam profile and follows a
path determined by refraction. The light intensity in the beamlet varies along that path
because of absorption and CBET with other beamlets. This diagnostic allows for a
detailed investigation of the effects of CBET on specific locations of the beam profile.
When each OMEGA beam is linearly polarized, the beamlet image is highly asymmetric
in terms of spot intensities. Symmetry is recovered when distributed polarization rotator
smoothing is used to split the polarization of each beam into two orthogonal polarizations.
By changing the time window of the gated images for nominally identical implosions, a
time-varying picture of CBET for linearly polarized beams can be constructed. It is
shown that early in time, spots in the beamlet images are symmetric as in polarization
smoothed implosions. The asymmetry in the beamlet spots appears during the main drive
part of the laser pulse when CBET is predicted to occur.
A fully 3-D CBET postprocessor for hydrodynamics codes is used to model the intensity,
wavelength, and polarization of each beamlet as it traverses the coronal plasma to the
diagnostic. The model predicts that the polarization dependence of CBET will results in
highly asymmetric unabsorbed light profiles for linearly polarized beams. The
unabsorbed light pattern is different for each beam and depends on the specific
polarizations of all crossing beams. An asymmetric beamlet spot image similar to that
recorded is predicted for linearly polarized beams.
this article.
23
T1-3
T1-4
Old Saybrook, CT
May 1-6, 2016
Spatial non-uniformity of crossed-beam energy transfer
C. Neuville, C. Baccou†, A. Debayle, P.-E. Masson-Laborde, M. Casanova, D. Marion,
P. Loiseau, S. Hüller††, C. Labaune† and S. Depierreux
CEA, DAM, DIF, F-91297 Arpajon, France
[email protected]
†
LULI - CNRS, Ecole Polytechnique, CEA, UPMC - 91128 Palaiseau cedex, France
††
Centre de Physique Théorique, UMR 7644 - 91128 Palaiseau cedex, France
The interaction of multiple beams in plasmas naturally occurs in the context of
laser fusion. It is also of interest for the amplification of short-pulse laser. When two
beams are crossing in a plasma, the density perturbation driven by their ponderomotive
beating can scatter energy of one of the beam in the direction of the other by induced
stimulated Brillouin scattering. For superimposed intensity from 1014 to 1015 W/cm2, this
mechanism is ruled by the plasma ion acoustic response. It can redistribute the energy
between incident and refracted beams or between co-propagating beams in direct- and
indirect-drive laser fusion experiments. For superimposed intensity higher than 1016
W/cm2, the perturbation can force the plasma ion acoustic response and scatter energy of
picosecond pulses in femtosecond pulses, resulting in short-pulse amplification.
An experiment was designed and done on the LULI2000 facility, at Ecole
Polytechnique (Palaiseau, France), to study crossed-beam energy transfer (CBET). Two
beams, a nanosecond beam and a picosecond beam, of same frequency were crossed in a
CH preformed plasma. Both beams were smoothed with random phase plates (RPP)
whose characteristics were chosen so that the picosecond beam focal spot (220µm
diameter) was twice larger than the nanosecond beam focal spot. This original
experimental setup enabled to cross the beams only in the lower part of the picosecond
beam focal spot. High resolution 2D spatial imaging diagnostics were used to measure
the focal spots of the beams after the crossing beams region and to directly observe
intensity profile modifications.
We will present this experiment and its main results. The amount of transferred
energy was first quantified as a function of the intensity of the two crossing beams.
Intensity profile modifications due to non-uniform CBET were observed thanks to the
imaging diagnostic set-up on the picosecond beam. This transverse non-uniformity of the
CBET appears to be mainly due to the saturation of CBET by the depletion of the beams.
Modifications in the speckle distribution functions were also observed. Simulations were
done, thanks to a recently developed code, SECHEL, for the conditions of this
experiment. These simulations reproduce the global energy transfer rates for moderate
intensities but fail in explaining the details of the intensity profile modifications. The
differences between the experiments and the modeling of CBET used in the simulations
will be discussed.
24
Old Saybrook, CT
May 1-6, 2016
The high-power, low-intensity approach to eliminating
stimulated Brillouin backscatter*
R. L. Berger, C. A. Thomas, K. L. Baker, A. B. Langdon,
D. J. Strozzi, C. S. Goyon, and D. P. Turnbull
Lawrence Livermore National Laboratory,
P.O. Box 808, Livermore, CA 94551, USA
[email protected]
The 64 NIF laser beams that make a 50o angle with the hohlraum axis have been
measured to reflect by Stimulated Brillouin Backscatter (SBS) enough laser light to cause
optical damage and limit hohlraum-design parameter space. The amount of backscatter
has been seen to depend on the initial plasma fill-density, the hohlraum wall material, and
the laser pulse length. The most important parameter causing SBS is the laser intensity
on the hohlraum wall. In many hohlraum designs, the power of the 50 degree beams was
reduced by cross-beam energy transfer (CBET)1 of the some of 44o and 50o beam power
to the 23o and the 30o beams. This scenario is associated with large stimulated Raman
scattering of the 23o and the 30o beams. Some recent designs with reduced CBET have
experienced high 50o SBS. Here we show that repointing beams and splitting beams
within a quad can reduce the laser intensity at the wall and still maintain adequate
polarization smoothing. The reduction in intensity is achieved by separating the 44o and
50o degree beams along the hohlraum axis and then repointing beams within each cone
azimuthally to reduce overlap.
PF3D2 simulations predict dramatic reductions of SBS. Experiments3 employing this
illumination strategy have coupled nearly 99% of the laser energy to the hohlraum.
* This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore
National Laboratory under Contract DE-AC52-07NA27344
1
P. Michel, et al. Phys. Rev. Lett. 102, 025004 (2009)
R. L. Berger, et al. Phys. Plasmas 5, 4337 (1998)
3
C. A. Thomas, et al. and J. Kline, et al this conference
2
25
T1-5
Old Saybrook, CT
May 1-6, 2016
T2-1
Simulation of 2D Kinetic Effects in Plasmas using the
Grid Based Continuum Code LOKI*
J. W. Banks1, B. Arrighi2, R. L. Berger2, S. Brunner3, T. Chapman2, B. I. Cohen2, J. A. F.
Hittinger2, T. M. Tran3, B. J. Winjum4
1
Rensselaer Polytechnic Institute, Department of Mathematical Sciences, Troy, NY 12180
2
Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, California 94551, USA
3
Centre de Recherches en Physique des Plasmas, Association EURATOM-Confédération Suisse,
Ecole Polytechnique Fédérale de Lausanne, CRPP-PPB, CH-1015 Lausanne, Switzerland
4
Department of Electrical Engineering, University of California Los Angeles, Los Angeles,
California 90095, USA
Kinetic simulation of multi-dimensional plasma waves through direct discretization of the
Vlasov equation is a useful tool to study many physical interactions and is particularly
attractive for situations where minimal fluctuation levels are desired, for instance, when
measuring growth rates of plasma wave instabilities. However, direct discretization of
phase space can be computationally expensive, and as a result there are few examples of
published results using Vlasov codes in more than a single configuration space
dimension. In an effort to fill this gap we have developed the Eulerian-based kinetic code
LOKI that evolves the Vlasov-Poisson system in 2+2-dimensional phase space. The code
is designed to reduce the cost of phase-space computation by using fully 4th order
accurate conservative finite differencing, while retaining excellent parallel scalability that
efficiently uses large scale computing resources. In this talk I will discuss the algorithms
used in the code as well as some aspects of their parallel implementation using MPI. I
will also overview simulation results of basic plasma wave instabilities relevant to laser
plasma interaction, which have been obtained using the code. These include simulations
of wavefront bowing and kinetic self focusing for electron-plasma waves (EPWs), growth
of transverse instability for EPWs and ion-acoustic waves (IAWs), and more recently the
effects of collisions on EPW and IAW propagation.
†
This work was performed under the auspices of the U.S. Department of Energy by Lawrence
Livermore National Laboratory under Contract No. DE-AC52-07NA27344 and funded by the
Laboratory Research and Development Program at LLNL under project tracking code 15-ERD038.
26
Old Saybrook, CT
May 1-6, 2016
Evidence of multibeam stimulated Brillouin scattering
in direct-drive inertial confinement fusion implosions*
W. Seka, J. F. Myatt, D. H. Edgell, S. P. Regan, and V. N. Goncharov
[email protected]
Sharply rising laser pulses are sometimes desirable for direct-drive inertial confinement
fusion experiments. Such pulses lead to rapidly increasing ablation that sends density and
velocity bumps (shelves) down the density gradient in the corona at the speed of sound.
Those velocity shelves are ideally suited for enhancing stimulated Brillouin scattering
(SBS) with a telltale spectral signature evolving from red- to blue-SBS shifts that are
easily detected and predicted from hydrodynamic simulations. The SBS signals may be
caused by either single-beam, hot-spot–driven SBS or multibeam SBS for which LLE’s
OMEGA Laser System is particularly well suited. Spherical irradiation experiments on
OMEGA are underway to tease out the details of the underlying SBS processes and to
assess their implications for the hydrodynamic drive of the implosions.
this article.
27
T2-2
Old Saybrook, CT
May 1-6, 2016
T2-3
2D2V fully kinetic simulations and nonlinear models of
ion acoustic waves relevant to stimulated Brillouin
scattering*
1
T. Chapman1, R. L. Berger1, J. W. Banks1, S. Brunner3, B. I. Cohen1, and B. Arrighi1
Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, California 94551, USA
Rensselaer Polytechnic Institute, Department of Mathematical Sciences, Troy, NY 12180
3
Centre de Recherches en Physique des Plasmas, Association EURATOM-Confédération Suisse,
Ecole Polytechnique Fédérale de Lausanne, CRPP-PPB, CH-1015 Lausanne, Switzerland
2
[email protected]
Stimulated Brillouin scattering (SBS) is sensitive to nonlinearities of the ion acoustic
wave (IAW) driven during this parametric instability. Particle trapping, both electron and
ion, may modify both the Landau damping and the nonlinear frequency of the IAW,
respectively reducing the SBS instability threshold and providing a mechanism of
saturation. Recent advances in modeling of IAWs in the form of fully kinetic 2D2V
simulations using the LOKI1 code have revealed the nature of the longitudinal and
transverse instabilities that IAWs themselves are subject to. Such IAW instabilities may
saturate SBS by interrupting the feedback loop required for SBS to grow2, and are an
important part of describing SBS at timescales greater than a few tens of ps.
Fluid simulations permit simulating laser-plasma interactions at experimentally relevant
scales that are not computationally feasible for fully kinetic codes. However, to describe
IAW nonlinearities, fluid codes require the inclusion of models of sub-grid kinetic
physics to be constructed. Previous attempts at describing sub-grid IAW nonlinearities in
SBS have included the aforementioned particle trapping effects or fluid nonlinearities3.
However, recent kinetic simulation advances permit more complete reduced models of
IAW nonlinearity to be constructed, allowing fluid simulations to describe a greater
parameter space (e.g., higher laser intensities and IAW amplitudes).
Here, we show recent 2D2V IAW simulations and summarize the basic reduced model
features necessary to describe them in a 3D fluid code such as pF3D4.
*This work was performed under the auspices of the U.S. Department of Energy (DOE)
by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 and
funded by the Laboratory Research and Development Program at LLNL under project
tracking code 15-ERD-038.
J. W. Banks et al., IEEE Trans. Plasma Sci. 38, 2198 (2010); Phys. Plasmas 18, 052102 (2011)
T. Chapman et al., Phys. Plasmas 22, 092116 (2015)
3
L. Divol et al., Phys. Plasmas 10, 3728 (2003); S. Hüller, Phys. Plasmas 13, 022703 (2006)
4
R. L. Berger et al., Phys. Plasmas 5, 4337 (1998)
1
2
28
Old Saybrook, CT
May 1-6, 2016
Simulating Stimulated Brillouin Scattering in NIF
Rugby Hohlraum Experiments Using pF3D *
S. H. Langer, P. Amendt, and A. B. Langdon†
7000 East Ave, L-472
Livermore, CA 94550
[email protected]
One of the first NIF experiments using a rugby-shaped hohlraum (shot N130502) had an
asymmetric implosion and relatively low levels of stimulated Brillouin scattering (SBS) 1.
This series of experiments used a low-adiabat (“low-foot”) pulse shape. Three changes
were made before the next shot to try and achieve a more symmetric implosion and
reduce levels of backscattered light. A small amount of neon was added to the helium gas
in the hohlraum, outer quadruplets of beams (“quads”) were repointed 500 µm closer to
the equator of the hohlraum, and outer quads were split by 800 µm in azimuth.
Substantial SBS from the outermost (50 deg.) cone of laser beams occurred during the
new experiment (shot N131011). We present simulation results of outer-beam SBS from
these targets, with the massively-parallel, paraxial envelope propagation code pF3D23.
The runs simulate a full quad of NIF laser beams over the 4.5 mm propagation length
from the laser entrance hole to the high-Z hohlraum wall and the full transverse extent of
the beam (2.87 mm x 2.74 mm) for ~100 ps during the peak of the laser pulse. The
speckled intensity pattern due to phase plates and the effects of polarization smoothing
are included. The runs utilized up to 1,572,864 cores of the IBM BlueGene/Q Sequoia
system at LLNL, and had up to 150 billion spatial zones. The results show that the
inclusion of neon had a small effect and repointing inward resulted in much higher SBS
levels. The effect of azimuthally splitting the beams in a quad is also discussed.
Simulated SBS spectra and the simulated spatial dependence at the NBI are compared to
experimental data.
* This work was performed under the auspices of the U.S. Department
of Energy by Lawrence Livermore National Laboratory under Contract
DE-AC52-07NA27344. Lawrence Livermore National Security, LLC. LLNL-ABS684222.
1
P. Amendt, J. S. Ross, J. L. Milovich, M. Schneider, E. Storm, D. A. Callahan, D. Hinkel, B. Lasinski, D.
Meeker, P. Michel, J. Moody, and D. Strozzi, Physics of Plasmas 21, 112703 (2014); doi:
10.1063/1.4901195
2
S. H. Langer, A. Bhatele, and C. H. Still. Comput. Sci. Eng., 16, 42 (2014).
3
R. L. Berger, C. H. Still, E. A. Williams, A. B. Langdon, Phys. Plasmas 5, 4337 (1998).
29
T2-4
T2-5
Old Saybrook, CT
May 1-6, 2016
Heat-flux measurements from collective Thomsonscattering spectra
R. J. Henchen,† S. X. Hu,† W. Rozmus,†† J. Katz,† and D. H. Froula†
†
[email protected]
††
University of Alberta, Edmonton, Canada T6G 2R3
Thomson-scattering measurements of plasma conditions are used to infer the Spitzer–
Härm flux (qSH = –κ∇Te) and are in good agreement with the values of the heat flux
measured from asymmetries in the electron plasma wave features. Heat-flux values
measure in the corona range from roughly 2% to 5% of the free-streaming flux
(qfs = neTevte). To study nonlocal thermal transport, large temperature gradients were
driven using a short-pulse (100-ps) laser in a coronal plasma. The relative amplitude of
the Thomson-scattered power into the up- and downshifted electron plasma wave features
was used to determine the flux of electrons moving along the temperature.
Simultaneously, the ion-acoustic wave features were measured. Their relative amplitude
was used to measure the flux of the return-current electrons. The frequencies of these ionacoustic and electron plasma wave features provided local measurements of the electron
temperature and density. These spectra were obtained at five locations along the
temperature gradient in a laser-produced blowoff plasma.
this article.
30
Poster Session
Old Saybrook, CT
May 1-6, 2016
2-D Highly-resolved Simulation Studies of Fill Tubes on
Ignition Double-Shell Targets for the NIF*
J.L. MILOVICH, P.A. AMENDT, S. SEPKE, J. KONING and M. MARINAK
Lawrence Livermore National Laboratory, Livermore CA 94551
[email protected]
Double-shell targets consist of two concentric shells: the outer layer is made out of a low-Z
material with high ablation efficiency, and the inner shell, mostly built of a high-Z material,
provides the in-situ confinement of radiation from the burning central DT fuel. This class of
target was studied early in the ignition program but set aside due to the concern that they
suffer significantly from the growth of short-wavelength perturbations. Recently, a new way
of controlling Rayleigh-Taylor instabilities that leverages state-of-the-art additive
manufacturing techniques has been identified. Designs with density-gradient inner shells as
well as material-matching metallic foams, which were shown via computer simulations to
mitigate the instabilities, are now within reach using these new fabrication techniques.
Numerical simulations mimicking the process of additive manufacturing, i.e., depositing
material in planar layers of controllable thickness, have found that the allowable limits on
the degree of density variations among the different “printed” layers are well within current
manufacturing capabilities [1]. These encouraging results have motivated studies on
possible methods to fill the inner shell with DT fuel. One of the attractive features of double
shells has been that they can, in principle, be fielded at room temperature using a diffusionfilling process requiring the inner capsule to be immersed in a high-pressure vessel of DT
fuel. Unfortunately, this technique would require significant cost and infra-structure
development. An alternative approach is the use of a thin fill tube as in DT-layered singleshell targets, suitably modified for double-shell targets. Simulations of a fill tube penetrating
both shells show a significant amount of inner-shell material injected into the burning fuel,
resulting in degraded performance. To mitigate this effect, other approaches are used to fill
the capsule, guided by 2-D simulation studies that will be described.
* Work performed under the auspices of U.S. Department of Energy by LLNL under Contract DE-AC52-
07NA27344 and supported by LDRD-14-ERD-031
________________________
1
J. L. Milovich et al., Phys Plasmas 11, 1552 (2004).
31
PT-1
PT-2
Old Saybrook, CT
May 1-6, 2016
Fast electron transport in different allotropes of shockheated carbon*
Christine M. Krauland, M. S. Wei†, W. Theobald★, J. Santos!, S. Zhang, F. N. Beg
Center for Energy Research, University of California – San Diego
9500 Gilman Drive
La Jolla, CA 92093
[email protected]
†
Inertial Fusion Technology, General Atomics
San Diego, CA 92121
★
Laboratory for Laser Energetic, University of Rochester
Rochester, NY 14623
!
Center for Intense Lasers and Applications, University of Bordeaux
Bordeaux, France
Understanding the transport physics of an intense relativistic electron beam in various
plasma regimes is crucial for many high-energy-density applications, such as fast heating
for advanced inertial confinement fusion schemes, equation of state and opacity
measurements, and ion sources. Most short pulse laser-matter interaction experiments for
electron transport studies have been performed with initially cold targets where the
resistivity is far from that in warm dense and hot dense plasmas. Additionally, the atomic
ordering of a target material can have a significant effect on the resistivity; if the ions are
highly disordered, then electrons will scatter incoherently and the electron mean free path
will be limited to the mean inter-ionic distance, leading to a higher resistivity as
compared to the more ordered lattice structure.1
We present results from a recent OMEGA EP experimental campaign that aimed
to characterize how the differences in resistivity affect electron transport and energy
coupling in initially cold and shock-heated samples of different carbon allotropes. We
used the OMEGA EP IR sidelighter beam (850 J, 10 ps) to irradiate a thin 10µm Al
coating on either vitreous carbon or single-crystal diamond to produce an electron beam.
In heated samples, we also employed a single UV beam (3.15 kJ, 1.8×1014 W/cm2) to
launch a shock into the respective material from the opposite side of the target. Transport
and energy deposition in each sample is inferred from the measured fast electron induced
fluorescence emission of a buried Cu tracer using a 2D spherical crystal imager and
calibrated x-ray spectrometers. Five electron spectrometers covering a 20° divergence
angle from the target axis are also fielded. All available data and particle-in-cell
simulations will be presented along with the experimental details.
*This work conducted under the auspices of the National Laser User Facility Program,
grant number DE-NA0002728.
P. McKenna, et al., “Effect of Lattice Structure on Energetic Electron Transport in Solids Irradiated by
Ultraintense Laser Pulses,” Physical Review Letters 106, 185004 (2011).
32
1
Old Saybrook, CT
May 1-6, 2016
Beyond nonlinear saturation of
backward Raman amplifiers
Ido Barth and Nathaniel J. Fisch
Princeton University Plasma Physics Laboratory
James Forrestal Campus
Princeton, NJ 08543
[email protected]
Backward Raman amplification is limited by relativistic nonlinear dephasing resulting in
saturation of the leading spike of the amplified pulse. Pump detuning is employed to
mitigate the relativistic phase mismatch and to overcome the associated saturation. The
amplified pulse can then be reshaped into a mono-spike pulse with little precursory
power ahead of it, with the maximum intensity increasing by a factor of two. This
detuning can be employed advantageously both in regimes where the group velocity
dispersion is unimportant and where the dispersion is important but small.1
This work was supported by NNSA Grant No. DE-NA0002948, AFOSR Grant No.
FA9550-15-1-0391, DOE Contract No. DE-AC02-09CH11466, and DTRA Grant No.
HDTRA1-11-1-0037.
1
I. Barth, Z. Toroker, A. A. Balakin, and N. J. Fisch, arXiv:1601.05832
[physics.plasm-ph] (2016).
33
PT-3
PT-4
Old Saybrook, CT
May 1-6, 2016
Transforming the idler for use in laser–plasma
interaction experiments*
S. Bucht, D. Haberberger, J. Bromage, and D. H. Froula
[email protected]
A novel optical system has been designed to transform the idler produced in an optical
parametric chirped-pulse–amplification (OPCPA) system into a useable high-power pulse
for laser–plasma interaction (LPI) experiments. The idler is an existing byproduct created
by all OPCPA systems and has similar bandwidth and energy to the signal; with proper
preparation it can be another high-fidelity laser pulse at a shifted or unique wavelength
from the signal. This preparation is made difficult because of two issues arising in the
optical parametric amplifier: (1) angular dispersion and (2) complex temporal chirp. A
two-prism angular dispersion compensator and a grism stretcher show promising analytic
solutions to these two problems without significantly sacrificing energy or bandwidth.
The unusual wavelength range of this beam makes it ideal for unique LPI experiments
such as Raman amplification.
this article.
34
Old Saybrook, CT
May 1-6, 2016
Dynamic Thomson scattering from nonlinear electron
plasma waves*
A. Davies, J. Katz, D. Haberberger, and D. H. Froula
[email protected]
Electron plasma waves (EPW’s) can be used to transfer significant energy from a long-pulse
laser to a short-pulse seed laser through the Raman scattering instability. Successful
implementation of Raman amplification could open an avenue to producing high-intensity
pulses beyond the capabilities of current laser technology (1022 W/cm2). This three-wave
interaction takes advantage of the plasma’s ability to sustain large-amplitude plasma waves.
Having complete knowledge of the EPW amplitude is essential to establishing optimal
parameters for high-efficiency Raman amplification. A dynamic Thomson-scattering
diagnostic is being developed to spatially and temporally resolve the amplitude of the driven
EPW’s. By imaging the scattered probe light onto a streak camera, the diffraction efficiency
of this plasma wave can be measured as a function of space and time. These data will be used
in conjunction with particle-in-cell simulations to determine the EPW’s spatial and temporal
profile. This will allow the effect of the EPW profile on Raman scattering to be
experimentally determined.
this article.
35
PT-5
PT-6
36
Old Saybrook, CT
May 1-6, 2016
Full-pulse particle-in-cell simulations of hot-electron
generation in OMEGA experiments*
E. Borwick, S. X. Hu,† J. Li,† R. Yan,† and C. Ren†,‡
Department of Mechanical Engineering, University of Rochester, Rochester, NY 14627
†
Laboratory for Laser Energetics, 250 East River Road, Rochester, NY 14623-1299
[email protected]
‡
Also with Department of Physics and Astronomy, University of Rochester
Rochester, NY 14627
Previous particle-in-cell (PIC) simulations on hot-electron generation in two-plasmon decay
in direct-drive inertial confinement fusion were done only for the condition at the peak
intensity of the laser driver and found more hot electrons than in previous experiments. 1,2
Using data from the LILAC hydrocode in conjunction with the PIC code OSIRIS, we now
perform several simulations sampling a 1-ns pulse to determine the evolution of hot-electron
generation as well as electron divergence during the pulse. The results will be compared with
the OMEGA experiments that measured hot-electron generation and divergence. 3
*This material is based upon work supported by the Department of Energy under Grant
Nos. DE-FC02-04ER54789 and DE-SC0012316 and by the National Science Foundation
under Grant No. PHY-1314734. The research used resources of the National Energy
Research Scientific Computing Center. The support of DOE does not constitute an
endorsement by DOE of the views expressed in this paper.
1
R. Yan et al., Phys. Rev. Lett. 108, 175002 (2012).
B. Yaakobi et al., Phys. Plasmas 20, 092706 (2013).
3
B. Yaakobi et al., Phys. Plasmas 16, 102703 (2009). 2
37
PT-7
PT-8
Old Saybrook, CT
May 1-6, 2016
Recent progress on understanding LWFA in the
nonlinear self-guided blowout regime*
Asher Davidson, P. Yu, X. Xu, F. S. Tsung, T. Dalichaouch, W. Lu†, W. An,
and W. B. Mori
UCLA
405 Hilgard Ave.
[email protected]
†
Tsinghua University
Beijing, China
We report on recent results on LWFA in the nonlinear, self-guided regime. In this regime
the wake is excited in the nonlinear blowout regime where the normalized vector
potential is larger than ~4. The laser is self-guided due to laser energy in the leading edge
being locally depleted before it diffracts. In the work of Lu et al., 1 matching conditions
for the laser spot size and pulse length were presented as well as scaling laws accelerated
electron energy in terms of laser and plasma parameters. These scaling laws were
compared against results for a 200 TW (6 Joule) laser. Recent advanced in PIC modeling,
including the quasi-3D and boosted frame techniques now make it possible to study these
scaling laws for higher laser intensities and laser energies. We use the quasi-3D version
of OSIRIS and boosted frame simulations using OSIRIS and UPIC-EMMA to examine
this nonlinear regime for existing and future 15-100 Joule lasers and compare the results
against the predictions of the scaling laws in Lu et al. We use the scaling laws to
determine how to optimize the results for a fixed laser energy including determining how
to optimize the electron beam energy through the laser pulse shape.
*This work supported by DOE and NSF.
1
Lu et al., PRSTAB 10, 061301 (2007).
38
PT-9
39
PT-10
Old Saybrook, CT
May 1-6, 2016
The UCLA Particle-in-Cell and Kinetic Simulation
Software Center (PICKSC)*
W. B. Mori, V. K. Decyk, F. S. Tsung, F. A. Fonseca†, B. J. Winjum, W. An, D.
Amorim†, T. N. Dalichaouch, A. Davidson, A. Joglekar, F. Li‡, J. May, A. Tableman, M.
Touati, X. Xu, and P. Yu
University of California at Los Angeles
405 Hilgard Ave.
[email protected]
†
Instituto Superior Tecnico
Lisbon, Portugal
‡
also with Tsinghua University
Beijing, China
The mission of the Particle-in-Cell and Kinetic Simulation Software Center (PICKSC) is
to support an international community of PIC and plasma kinetic software developers,
users, and educators, and to increase the use of PIC software for accelerating the rate of
scientific discovery. PICKSC aims to make available and document illustrative opensource software programs for different computing software, a flexible open-source
Framework for rapid construction of parallelized PIC programs, and distinct production
programs; to host activities on developing and comparing different PIC algorithms and on
documenting best practices for developing and using PIC programs; to coordinate a
community development of educational software for undergraduate and graduate courses
in plasma physics and computer science; and to sponsor an annual workshop to help build
a community of developers and users. We will describe some recent progress and
activities within PICKSC.
*Work supported by NSF and DOE.
40
Old Saybrook, CT
May 1-6, 2016
W1-1
Raman Amplifiers for Fast Igniter Pulses
Presenter James Sadler
Naren Ratan, Luke Ceurvorst,
Muhammad Kasim and Peter Norreys
University of Oxford
Clarendon Laboratory, Parks Road
Oxford, OX1 3PU, England
[email protected]
Optimal performance is found for a seed pulse with increasing power towards the rear.
Two dimensional simulations also demonstrate that the transverse coherence is retained
through the plasma interaction. A major advantage, of interest to penetrating high density
ICF plasmas, is that the compression scheme is just as effective at 3ω. A plausible design
for generating a fast igniter pulse of energy 50kJ+ at 3ω is explored.
The authors acknowledge the Osiris Consortium and are grateful for HPC resources at the
STFC Scarf facility and the Archer supercomputer
41
Wednesday
Plasma laser pulse amplifiers could potentially compress pulses at intensities 1000 times
greater than solid state gratings, vastly reducing the size and cost of apparatus. I will
present Particle-in-Cell simulations exploring the plethora of different regimes, bounded
by considerations of energy transfer efficiency and mitigating competing plasma
instabilities.
W1-2
42
Old Saybrook, CT
May 1-6, 2016
Experimental Investigation of Self-Diffraction from
Laser Generated Plasma Gratings*
S. E. Schrauth, R. Luthi, R. Plummer, B. Hollingsworth, W. Carr, M. Norton, R. Wallace,
A. Hamza, B. MacGowan, M. Shaw, M. Spaeth, K. Manes, JM Di Nicola and P. Michel
7000 East Ave
Livermore, California 94550
[email protected]
We are investigating the formation and diffraction efficiency of plasma gratings
generated by the interference of two laser beams crossing at a small angle as they reflect
off the surface of a solid (aluminum) target. In particular, we have characterized
conditions under which diffraction occurs in the “Raman-Nath” regime (thin grating,
presence of higher-order spatial diffraction modes). Such high-order gratings were
observed during some National Ignition Facility experiments. Recent experiments were
performed on the Optical Sciences Laser using a simpler geometry with only two
interfering beams with the goal to investigate further this effect. High diffraction
efficiency into higher-order modes has been observed at relatively low laser intensities
(~1012 W/cm2, λ0=1.053 µm). These results are relevant to crossed-beam energy transfer
for ICF experiments, where scattering into higher-order modes is typically not
considered, as well as for the development of high-efficiency plasma-based surface
gratings for plasma photonics applications.
order:
-2
-1
0
0
+1
+2
LLNL-ABS-684541
43
W1-3
W1-4
Old Saybrook, CT
May 1-6, 2016
Collective SRS driven by two side-by-side, copropagating, picosecond laser pulses
C. Rousseaux, K. Glize, S.D. Baton1, L. Lancia2, D. Bénisti, L. Gremillet
1
CEA, DAM, DIF, F-91297 Arpajon, France
LULI – CNRS, Ecole Polytechnique, CEA: Université Paris-Saclay; UPMC Univ.
Paris 06: Sorbonne Universités–, F-91128 Palaiseau cedex, France
2
Dipartimento SBAI, Università di Roma “La Sapienza”, 00161 Roma, Italy
[email protected]
In this presentation, recent experiments carried out at the LULI facility investigate the
backward stimulated Raman scattering (SRS) of two co-propagating 1-µm, 1.5-ps
FWHM laser pulses focused side-by-side, but not simultaneously, in a preformed
underdense plasma. For the first time, it is experimentally demonstrated that a weakintensity speckle, ineffective when fired alone in a preformed plasma, yields a significant
SRS-induced reflectivity if it is launched a few picoseconds after a strong one. The data
have been obtained by using both highly space- and time-resolved Thomson diagnostics
and space-resolved SRS reflectivity measurements. They provide unprecedented insight
into the interaction processes of laser-driven parametric instabilities, showing the role of
either electrostatic or electromagnetic seeding for SRS enhancements in weak-intensity
speckles. A major finding is that the electrostatic seeding, which mediates the coupling
between two cross-polarized speckles, is found to play a significant role over
unexpectedly long times (~15-20 ps under our experimental conditions). State-of-the-art
particle-in-cell numerical simulations confirm the destabilizing effect of the strong
speckle over the weak one, and the importance of seeding for multispeckle interaction.
44
Old Saybrook, CT
May 1-6, 2016
Advances in particle driven plasma wakefield
accelerators at FACET *
Navid Vafaei-Najafabadi1, E. Adli2,3, J. A. Allen2, W. An1, C. I. Clarke2, C. E. Clayton1,
S. Corde2,4, J. P. Delahaye2, E. J. England2, A. S. Fisher2, J. Frederico2, S. Gessner2, S. Z.
Green2, M. J. Hogan2, C. Joshi1, N. Lipkowitz2, M. Litos2, W. Lu1,5, K. A. Marsh1, W. B.
Mori1, P. Muggli6, M. Schmeltz2, D. Walz2, G. White2, Z. Wu2, V. Yakimenko2, G.
Yocky2
1
405 Hilgard Avenue
navidvafa @ucla.edu
2
SLAC National Accelerator Laboratory, Menlo Park, CA 90034
3
Currently at Department of Physics, University of Oslo, 0316Oslo, Norway. 4
Currently at LOA, ENSTAParisTech, CNRS, Ecole Polytechnique, Universite ́ ParisSaclay,91762Palaiseau, France.
5
Department of Engineering Physics, Tsinghua University, Beijing 100084, China
The accelerating field of a plasma wakefield is more than two orders of magnitude higher
than RF-based accelerators. The Facility for Advanced Accelerator Experimental Test
(FACET) at the SLAC National Accelerator Laboratory was commissioned to
experimentally examine the properties of such wakefields. The 2-km, RF-based linac at
FACET provided an electron or positron beam with 20 GeV of energy and up to 3 nC of
charge, which was subsequently used as a driver of a nonlinear plasma wave. This talk
will present the experimental results that provide the evidence for plasma wakefield as
capable of making compact, efficient accelerators. Specifically, a wakefield driven by an
electron beam accelerated a trailing bunch of 74 pC at a rate of 5 GeV/m with an energy
transfer efficiency from the driver to trailing beam of 30%. In the positron-driven wake, a
new regime of wakefield was discovered, where the evolution of the nonlinear plasma
wave created a focusing and accelerating region such that a substantial number of
positrons were accelerated at a gradient of 3.8 GeV/m and with an efficiency of 30% as
well. Additional evidence for generation of an ultra-low emittance beam, which is
required for creating bright beams from these plasma accelerators will also be discussed.
*The work at UCLA was supported by DOE Grant No. DE-SC0010064. Work at SLAC
was supported by the DOE Contract No. DE-AC02-76SF00515.
45
W2-1
W2-2
Old Saybrook, CT
May 1-6, 2016
Planar laser–plasma interaction experiments
at direct-drive ignition-relevant scale lengths
M. J. Rosenberg,† A. A. Solodov,† W. Seka,† J. F. Myatt,† S. P. Regan,†
M. Hohenberger,† R. Epstein,† T. J. B. Collins,† P. A. Michel,†† D. P. Turnbull,††
C. Goyon,†† J. E. Ralph,†† M. A. Barrios,†† and J. D. Moody††
†
[email protected]
††
Livermore, CA 94550
Results from the first experiments at the National Ignition Facility to probe laser–plasma
interaction (LPI) hot-electron production at scale lengths relevant to direct-drive ignition
are reported. The irradiation on one side of planar CH foils generated a plasma at the
quarter-critical surface with predicted density gradient scale lengths of Ln ~ 600 µm,
measured electron temperatures of Te ~ 3.5 to 4.0 keV, overlapped laser intensities of I ~
6 to 12 × 1014 W/cm2, and predicted two-plasmon–decay (TPD) threshold parameters of
η ~ 4 to 8. The hard x-ray spectrum was measured to infer the hot-electron temperature
and the fraction of total laser energy converted to LPI hot electrons. Optical emission
from stimulated Raman scattering and at ω /2 (attributed to TPD) are correlated with the
time-dependent hard x-ray signal. The effect of laser beam angle of incidence on hotelectron generation was assessed, and the data show that the beam angle of incidence did
not have a strong effect. The fraction of laser energy converted to hot electrons was found
to increase from ~0.5% to ~2.3% as the laser intensity at the quarter-critical surface
increased from ~6 to 12 × 1014 W/cm2, while the hot electron temperature was nearly
constant around 40 to 50 keV. These results will be used to benchmark simulations of
LPI hot-electron production at conditions relevant to direct-drive ignition-scale
implosions and also to guide hot-electron mitigation efforts.
this article.
46
Old Saybrook, CT
May 1-6, 2016
Modeling of laser–plasma interaction experiments
at direct-drive ignition-relevant plasma conditions
A. A. Solodov,† M. J. Rosenberg,† J. F. Myatt,† R. Epstein,† S. P. Regan,† W. Seka,† J. G.
Shaw,† M. Hohenberger,† J. W. Bates,†† P. A. Michel,‡ J. D. Moody,‡ J. E. Ralph,‡ D. P.
Turnbull,‡ and M. A. Barrios‡
†
Laboratory of Laser Energetics, University of Rochester
250 East River Road, Rochester NY 14623-1299
[email protected]
††
Naval Research Laboratory, Washington, DC 20375
‡
Lawrence Livermore National Laboratory, Livermore, CA 94550
Laser–plasma interaction instabilities, such as two-plasmon decay (TPD) and stimulated
Raman scattering (SRS), can be detrimental for direct-drive inertial confinement fusion
because of target preheat by generated high-energy electrons and anomalous laser energy
dissipation before the quarter-critical density surface. The radiation–hydrodynamics code
DRACO has been used to design planar-target experiments that generate plasma and
interaction conditions relevant to ignition direct-drive designs (IL ~ 1015 W/cm2, Te >
3 keV, density gradient scale lengths of Ln ~ 600 m). The use of planar targets makes it
possible for TPD and SRS to be decoupled from cross-beam energy transfer, which
reduces the laser absorption in current National Ignition Facility (NIF) direct-drive–
implosion experiments. Different laser-irradiation geometries allow effect of laser beam
angle of incidence on hot-electron production to be studied. The laser–plasma interaction
code LPSE has been used to investigate TPD using the predicted plasma profiles and
laser-irradiation geometry in three dimensions. The energetic electrons generated by TPD
and/or SRS are propagated into the planar target using the electron–photon Monte Carlo
transport code EGSnrc. This enables a direct comparison between the simulated and
experimentally observed Mo K fluorescence and hard x-ray bremsstrahlung emission.
The hot-electron temperature of Thot ~ 40 to 50 keV and the fraction of total laser energy
converted to hot electrons of ~1% have been inferred. The plasma profiles have been
post-processed for backscatter SRS and stimulated Brillouin scattering gains.
Comparisons of the simulation results with recent experiments on the NIF and the
implications for ignition-scale direct-drive experiments will be presented.
this article.
47
W2-3
Old Saybrook, CT
May 1-6, 2016
W2-4
Kinetic analysis of convective stimulated Raman
scattering and its potential as a temperature diagnostic
R. W. Short, W. Seka, and J. F. Myatt
[email protected]
In recent years stimulated Raman scattering (SRS) spectra with improved spectral and
temporal resolution have become available, renewing interest in such spectra as a
diagnostic for conditions in the underdense corona. In the early 1980s attempts were
made to use kinetic analysis of SRS emission, including collisional absorption and a
blackbody source, as a temperature diagnostic. 1 Results were mixed, and discrepancies
were ascribed to such factors as filamentation, density plateaus, and inaccurate fluxlimited modeling of temperature. Here the analysis is revisited and extended to oblique
incidence and observation angles. The results show promise for such analysis as a
temperature diagnostic.
This material is based upon work supported by the Department of Energy National
this article.
1
W. Seka et al., Phys. Fluids 27, 2181 (1984).
48
Old Saybrook, CT
May 1-6, 2016
Simulation of stimulated Brillouin scattering and
stimulated Raman scattering in shock ignition*
L. Hao, J. Li, W.-D. Liu, R. Yan, and C. Ren†
Laboratory for Laser Energetics, Fusion Science Center for Extreme States of Matter, and
Department of Mechanical Engineering, University of Rochester, 250 East River Road,
Rochester, NY 14623-1299
[email protected]
†
Also with Department of Physics and Astronomy, University of Rochester,
Rochester, NY 14627
We study stimulated Brillouin scattering (SBS) and stimulated Raman scattering (SRS) in
shock ignition by comparing fluid and particle-in-cell (PIC) simulations. Under typical
parameters for the OMEGA experiments, 1 a series of 1-D fluid simulations with laser
intensities ranging between 2 × 1015 and 2 × 1016 W/cm2 finds that SBS is the dominant
instability, which increases significantly with the incident intensity. Strong pump
depletion caused by SBS and SRS may limit the transmitted intensity at the 0.17 nc to be
less than 3.5 × 1015 W/cm2. The PIC simulations show similar physics but with higher
saturation levels for SBS and SRS convective modes and stronger pump depletion
resulting from higher seed levels for the electromagnetic fields in PIC codes. Plasmaflow profiles are found to be important in proper modeling of SBS and limiting its
reflectivity in both the fluid and PIC simulations.
Nos. DE-FC02-04ER54789 and DE-SC0012316; by National Science Foundation under
Grant No. PHY-1314734; and by National Natural Science Foundation of China (NSFC)
under Grant No. 11129503. The research used resources of the National Energy Research
Scientific Computing Center. This material is also based upon work supported by the
Department of Energy National Nuclear Security Administration under Award Number
DE-NA0001944; the University of Rochester; and the New York State Energy Research
and Development Authority. The support of DOE does not constitute an endorsement by
DOE of the views expressed in this paper.
1
W. Theobald et al, Phys. Plasmas 19, 102706 (2012).
49
W2-5
W2-6
Old Saybrook, CT
May 1-6, 2016
Density modulation-induced absolute laser-plasmainstabilities: simulations and theory*
J. Li, R. Yan, and C. Ren†
Laboratory for Laser Energetics, Fusion Science Center for Extreme States of Matter, and
Department of Mechanical Engineering, University of Rochester, 250 East River Road,
Rochester, NY 14623-1299
[email protected]
†Also with Department of Physics and Astronomy, University of Rochester,
Rochester, NY 14627
Fluid simulations show that when a static sinusoidal density modulation is superimposed
on a linear density profile, convective instabilities can become absolutely unstable. This
conversion can occur for two-plasmon–decay and stimulated Raman scattering
instabilities under realistic direct-drive inertial confinement fusion conditions and can
affect hot-electron generation and laser-energy deposition. Analysis of the three-wave
model shows that a sufficiently large change of the density gradient in a linear density
profile can turn convective instabilities into absolute ones. An analytical expression
is given for the threshold of the gradient change, which depends only on the
convective gain.
Nos. DE-FC02-04ER54789 and DE-SC0012316; by National Science Foundation under
Grant No. PHY-1314734; and by National Natural Science Foundation of China (NSFC)
under Grant No. 11129503. The research used resources of the National Energy Research
Scientific Computing Center. This material is also based upon work supported by the
Department of Energy National Nuclear Security Administration under Award Number
DE-NA0001944; the University of Rochester; and the New York State Energy Research
and Development Authority. The support of DOE does not constitute an endorsement by
DOE of the views expressed in this paper.
50
Old Saybrook, CT
May 1-6, 2016
The National Ignition Facility: An unexpected journey,
lessons to be learned to secure projects of scale,
and perspectives on the future of inertial confinement
fusion research*
E. M. Campbell
[email protected]
Developing the mission, science, technology, and support for projects of scale is a
demanding and multifaceted enterprise. There are many lessons to be learned from the
National Ignition Facility (NIF) experience that can be applied in the quest to secure any
future large-scale facility. This presentation will include a historical perspective on
inertial confinement fusion (ICF) at Lawrence Livermore National Laboratory and the
Stockpile Stewardship Program that motivated the NIF, the scientific and political
strategy that ultimately secured the Facility, and the perspectives on the future of
ICF research.
*This material is based upon work supported by the University of Rochester.
51
W3-1
Poster Session
Old Saybrook, CT
May 1-6, 2016
PW-1
Vlasov Fokker Planck modeling of high energy density
A. Tableman and W. B. Mori
Department of Physics & Astronomy, UCLA
405 Hilgard Ave.
[email protected]
Vlasov-Fokker-Planck simulations can be applied to a wide variety of problems in High
Energy-DensityPlasmas. Like standard Vlasov codes, they can used to study small
timescale kinetic physics such as the waves in plasma media, including Landau Damping,
echoes, and instabilities with the added ability to probe the effect of collisions –
especially important in high density scenarios. Moreover, when an implicit solver is
employed, Vlasov-Fokker-Planck simulations enable the study of kinetic effects in
simulations over realistic temporal and spatial problems – important, for example, in
examining various transport phenomena. Recent simulations with the VFP code
OSHUN 1 will be presented for all of the aforementioned problems. The algorithmic
improvements that have facilitated these studies will also be discussed.
1
M. Tzoufras, A.R. Bell, P.A. Norreys, F.S. Tsung, JCP 230 (17), 6475-6494 (2011); M. Tzoufras, A.
Tableman, F.S. Tsung, W.B. Mori, A.R. Bell, Phys.
52 Plasmas 20, 056303 (2013).
Old Saybrook, CT
May 1-6, 2016
Behavior of NIF Hohlraums with Beryllium Capsules*
D. C. Wilson, S.A. Yi, A. N. Simakov, W.S. Daughton, J.L. Kline ,D.S. Montgomery, G.
A. Kyrala, R.E. Olson, E.L. Dewald†, J. E. Ralph†, E.C. Merritt, E.N. Loomis, D. J.
Strozzi† , R. Tommasini†, M. B. Schneider†, J. R. Rygg†, N. Izumi†, T. Ma†, H. Chen†, N.
E. Palmer†, A. G. MacPhee†, S. F. Khan†, J.L. Milovich†, D. E. Hinkel†, D.A. Callahan†,
O. Jones†, P. A. Amendt†,T. S. Perry, S. Batha,
P.O.Box 1663
Los Alamos, New Mexico, 87544
[email protected]
†
Livermore, California, 94551
Beryllium capsules have been fielded in gold hohlraums at the National Ignition Facility
since August 2014. A single capsule size has been fielded in both 5750 and 6720 µm
diameter gold hohlraums at helium gas fill densities of 1.6, 0.6, 0.3, and 0.15 mg/cc. A
second, slightly larger capsule, was also tested as the surrogate outer shell of a double
shell target at 0.032 mg/cc. At 1.6 mg/cc gas fill and with a similar laser pulse to that
used for a CH capsule, the beryllium capsule hohlraum produced slightly more SRS from
the inner cones. With a 9 ns pulse in a 6720 hohlraum some inner cone SRS remains, but
outer cone SBS arises. With a 5 ns trapezoidal pulse in a 5750 hohlraum using the outer
shell of a double shell target, backscatter is nearly eliminated. As backscatter is reduced,
the laser drive multipliers increase towards 1.0. We will discuss the impact of beryllium
capsules on backscatter, drive multipliers, and symmetry as derived from Dante data,
laser entrance hole closure, x-ray bangtime, and time dependent Cu backlighter
transmission (1D and 2D ConAs).
* This work was performed at Los Alamos and Lawrence Livermore National
Laboratories, funded by the US Department of Energy.
53
PW-2
PW-3
Old Saybrook, CT
May 1-6, 2016
PIC Simulation of Nuclear EMP *
W. A. Farmer, B. I. Cohen, C. D. Eng, A. Friedman, D. P. Grote, H. W. Kruger, and D. J.
Larson
7000 East Ave.
Livermore, CA 94550
[email protected]
The early time signal of nuclear EMP has historically been simulated using various
approximations1 developed to make the problem tractable on computing infrastructure
that existed in the 1970’s and 80’s. These include the obliquity factor (a statistically
averaged treatment of multiple scattering by fast electrons), the high-frequency
approximation (which reduces the electromagnetic field equations to a spherically
symmetric form), and a fluid treatment of the background electrons.
This study reports on a new code, EMPulse, developed for the simulation of nuclear
EMP. EMPulse will allow for the description of three-dimensional effects and relaxes
many of the approximations present in legacy codes. This newer code is based on the
open-source Warp particle-in-cell framework2. Here, we describe the underlying Warp
framework and its capabilities and the models that have been or are being newly
developed and incorporated into EMPulse. Benchmarking studies are shown, in which
EMPulse is compared to another code, CHAP-lite3, which is based on legacy EMP code
framework. We further report on the validity of the obliquity factor, which may have uses
beyond nuclear EMP modeling.
*This work was performed under the auspices of the U.S. DOE by Lawrence Livermore
National Security, LLC, Lawrence Livermore National Laboratory under Contract DEAC52-07NA27344.
H. J. Longley and C. L. Longmire, “Development of the CHAP EMP Code,” Defense Nuclear Agency,
Alexandria, VA, Rep. DNA-3150T, Nov. 1973.
2
D. P. Grote, A. Friedman, J.-L. Vay, and I. Haber, “The Warp code: Modeling high intensity ion beams,”
AIP Conf. Proc., Vol. 749, no. 1, pp. 55-58 (2005).
3
W. A. Farmer, B. I. Cohen, and C. D. Eng, “On the validity of certain approximations used in the
modeling of nuclear EMP,” IEEE Trans. Nucl. Sci.,
54 (in press).
1
Old Saybrook, CT
May 1-6, 2016
The Kinetic Behavior of Stimulated Raman Scattering
in the Presence of External Magnetic Fields*
B. J. Winjum, A. Tableman, F. S. Tsung, W. B. Mori
[email protected]
An external magnetic field (B0) can modify the kinetic evolution of stimulated Raman
scattering (SRS) by altering the phasespace dynamics of trapped particles. Using oneand two-dimensional (1D and 2D) particle-in-cell simulations, we show the effect of B0
on SRS reflectivity, trapped particle motion, and local heating. 1D simulations (one space
and three velocity dimensions) show that the rotation of resonant particles in velocity
space by B0 aligned perpendicular to the laser wavevector can increase the threshold for
kinetically inflated SRS and decrease SRS reflectivity by increasing the damping rate and
limiting trapped particle motion along the laser propagation direction. On the other hand,
if nonlinear effects such as detuning are altered more than the damping, B0 can also
increase reflectivity by maintaining the SRS resonance. 2D simulations of SRS in singleand multi-speckled laser beams further show the effect of external magnetic fields on the
spatial dynamics of resonant particles, with the field restricting the motion of resonant
particles within, into, and out of an unstable region. For certain parameters, B0 can
completely eliminate kinetic SRS.
*This work was supported by the DOE under Grant No. DE-NA0001833. Simulations
were carried out on the Dawson2 cluster at UCLA, Edison at NERSC, Mira at ALCF, and
BlueWaters at NCSA.
55
PW-4
PW-5
Old Saybrook, CT
May 1-6, 2016
Laser Backscatter Measurements
from MagLIF Targets on Z*
David E. Bliss, M. Geissel, M.E. Campbell† and W.D. Seka†
Sandia National Laboratories
PO Box 5800
Albuquerque, NM 87185
[email protected]
†
University of Rochester – Laboratory for Laser Energetics
Rochester, NY 14623
The Magnetized Liner Inertial Fusion (MagLIF) concept requires preheat of the gas to
achieve significant yield. Without preheat, the fuel starts on a low pressure, low
temperature adiabat and the liner can do little work on the fuel until excessively high
convergence ratios, r0/rf, are reached, where r0 and rf are the initial and final radius of
the gas-liner interface. Preheating to start the fuel on a higher adiabat allows the liner
to do more work on the fuel before instabilities can disrupt the implosion. For MagLIF
experiments on Z, the Z Beamlet Laser (ZBL) is the source of pre-heat. Characterization
of the laser-target coupling is critical to understanding MagLIF performance. Laser
Plasma Instabilities (LPI) resulting from the interaction of the laser with the Laser
Entrance Window and the gas can limit the deposition of energy into the fuel or possibly
worse redirect laser energy into the liner wall creating mix. We present time-resolved
laser backscatter spectra recorded on a visible streak camera coupled to a
spectrometer. Results are compared to simple models to explain the origin of spectral
features.
*Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation,
a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National
Nuclear Security Administration under contract DE-AC04-94AL85000.
56
Old Saybrook, CT
May 1-6, 2016
3-D Simulations of Magnetized Direct-Drive ICF
Implosions
C. A. Walsh and J. P. Chittenden
Imperial College London
Exhibition Road
London, SW7 2AZ
[email protected]
Applied magnetic fields have previously been used to increase the electron temperature in
direct-drive ICF implosions by 15%, corresponding to an increased fusion yield of 30%.1
Compressed magnetic fields of up to 4000T have been measured using this method,
resulting in a highly magnetized hot-spot and significant electron thermal conduction
suppression without the magnetic pressure directly affecting the dynamics of the plasma. 2
Here 3-D extended-MHD simulations of cylindrical flux compression experiments are
presented with anisotropic heat conduction and magnetic field transport by advection
with bulk flow, resistive diffusion and Nernst advection down temperature gradients. The
magnetic field distribution is found to deviate greatly from the 'frozen-in-flow'
approximation.
Realistic asymmetric surface intensities are used, resulting in a considerably deformed
hot-spot. An energy balance is presented, highlighting the changing importance of
magnetization for an asymmetric hot-spot (which has a larger surface area between the
hot low-density fuel and the cold high-density fuel) compared with the 1-D case.
The effect of the Nernst advection can be separated into 3 stages:
1. Suppression of heat front during coast phase, resulting in a lower adiabat of
compressed fuel.
2. Early hot-spot formation is more magnetized.
3. Later hot-spot leaks magnetic field down temperature gradients and is therefore less
magnetized.
The relative importance of each of these stages is quantified. Comparisons with
experimental proton deflectometry results are also made.
M. Hohenberger et al., “Inertial confinement fusion implosions with imposed magnetic field compression
using the OMEGA Laser”, Phys. Plasmas 19, 056306 (2012).
2
J. P. Knauer et al., “Compressing magnetic fields with high-energy lasers”, Phys. Plasmas 17, 056318
(2010)
57
1
PW-6
PW-7
Old Saybrook, CT
May 1-6, 2016
Analysis of laser filamentation in Sandia MagLIF
experiments*
Andrew J. Schmitt, Adam Harvey-Thompson†, and Adam Sefkow†
Laser Plasma Branch, Plasma Physics Division
Code 6730, Naval Research Laboratory
[email protected]
†
The magnetized liner inertial fusion (MagLIF) concept is an approach intended to
generate thermonuclear fusion energy using a Z-pinch to compress and heat a core of
preheated DT gas.1 One of the concerns in early experiments is efficient coupling of the
pre-heating laser pulse to the core gas. This issue of core heating was the subject of
recent experiments2 on the University of Rochester Omega EP facility which imaged
laser heating in a magnetized underdense plasma using x-rays.
We present simulations of the plasma conditions and the expected filamentation behavior
of the laser propagation in these experiments using the FASTRAD3D radiation
hydrocode and a paraxial-based laser propagation code that was previously used to
analyze laser propagation in icf environments3. We show, via these simulations and a
theoretical analysis, that laser filamentation is not expected under the conditions of this
experiment.
*This work supported by US DoE/NNSA.
A.B. Sefkow, S.A. Slutz, J.M. Koning, M.M. Marinak, K.J. Peterson, D.B. Sinars and R.A. Vesey,
"Design of magnetized liner inertial fusion experiments using the Z facility", Phys. Plasmas 21, 072711
(2014).
2
Adam Harvey-Thompson, “Investigating the laser heating of underdense plasmas at conditions relevant
to MagLIF”, APS/DPP conference Savannah, GA [http://meetings.aps.org/link/BAPS.2015.DPP.GI3.5]
(2015).
3
Andrew J. Schmitt and Bedros B. Afeyan, “Time-dependent filamentation and stimulated Brillouin
forward scattering in inertial confinement fusion58plasmas”, Phys. Plasmas 5, 503 (1998).
1
PW-8
59
PW-9
Old Saybrook, CT
May 1-6, 2016
On the numerical simulation of the ablative RayleighTaylor instability in laser-fusion targets using the
FastRad3D code*
J.W. Bates, A.J. Schmitt and S.T. Zalesak
U.S. Naval Research Laboratory
4555 Overlook Avenue, SW
[email protected]
The ablative Rayleigh-Taylor (RT) instability is a key factor in the performance of
directly-drive inertial-confinement-fusion targets. Although this subject has a long
history, the accurate simulation of the ablative RT instability has proven to be a
challenging task for many radiation hydrodynamics codes, particularly when it comes to
capturing the ablatively-stabilized region of the linear dispersion spectrum and modeling
ab initio perturbations. In this poster, we present results from recent two-dimensional
numerical simulations of the ablative RT instability that were performed using the
Eulerian code FastRad3D at the U.S. Naval Research Laboratory. We consider low and
moderate-Z target materials, third- and quarter-micron laser wavelengths, high and low
intensities and where possible, compare our findings with experiment data. Growth rates
of single wavelength modes are determined by calculating the areal mass perturbation
through the entire target in accordance with most experimental measurements of this
instability. The linear dispersion relations determined in this way are generally consistent
with the formulae reported by Betti et al. [Phys. Plasmas 5, 1446 (1998)].
*Work supported by the U.S. Department of Eenergy.
60
Old Saybrook, CT
May 1-6, 2016
R1-1
An overview of laser-driven magnetized liner inertial
fusion on OMEGA*
J. R. Davies, D. H. Barnak, R. Betti, P.-Y. Chang, K. J. Peterson,† A. B. Sefkow,†
D. B. Sinars,† and S. A. Slutz†
[email protected]
†
Sandia National Laboratories, Albuquerque, NM 87185
MagLIF (magnetized liner inertial fusion) relies on cylindrical compression of preheated
and magnetized fuel. Originally proposed as a pulsed-power scheme (using the
Z machine at Sandia National Laboratories to compress the target and a single laser beam
for preheating)1 the same approach could be taken using lasers for preheating and
compression. A point design for laser-driven MagLIF on the OMEGA laser is presented,
using MIFEDS (magneto-inertial fusion electrical discharge system)2 to provide a 10-T
axial magnetic field, a single OMEGA beam to preheat the fuel up to 200 eV, and 40
OMEGA beams to compress the target. The energy that can be delivered to a target on
OMEGA is ~1000 lower than can be delivered on Z, so target linear dimensions are
reduced by factors of roughly 10. The objectives of this mini-MagLIF program are to
provide the first experimental data on MagLIF scaling and to provide more shots with
better diagnostic access than on Z. Results from the first OMEGA experiments studying
preheat and compression individually will be presented.
1
S. A. Slutz et al., Phys. Plasmas 17, 056303 (2010).
G. Fiksel et al., Rev. Sci. Instrum. 86, 016105 (2015).
2
61
Thursday
*The information, data, or work presented herein was funded in part by the Advanced
Research Projects Agency-Energy (ARPA-E), U.S. Department of Energy, under Award
Number DE-AR0000568, the Department of Energy National Nuclear Security
Administration under Award Number DE-NA0001944, the University of Rochester, and
the New York State Research and Development Authority. The views and opinions of
authors expressed herein do not necessarily state or reflect those of the United States
Government or any agency thereof
R1-2
Old Saybrook, CT
May 1-6, 2016
Scaling laser-driven MagLIF to the NIF*
D. H. Barnak, R. Betti, E. M. Campbell, P.-Y. Chang, J. R. Davies, J. P. Knauer, K. J.
Peterson,† S. P. Regan, A. B. Sefkow,† D. B. Sinars,† and S. A. Slutz,† and G. Fiksel‡
[email protected]
†
Sandia National Laboratories, Albuquerque, NM 87185
‡
University of Michigan, Ann Arbor, MI 48109
MagLIF (magnetized liner inertial fusion) relies on cylindrical compression of preheated
and magnetized fuel. Originally proposed as a pulsed-power scheme, using the Z machine
at Sandia National Laboratories to compress the target and a single laser beam for
preheating, 1 the same approach could be taken using lasers for preheating and
compression. A point design for laser-driven MagLIF on OMEGA has been developed
and aspects of this design have been tested in experiments. Scaling of this point design to
NIF (National Ignition Facility)-relevant energies is presented, considering experimentrelevant quantities for the initial heating of the fuel and the initial magnetic field. The
scaling relations for MagLIF are compared to a more traditional hydro-equivalent scaling
and key non-scalable physics issues are identified. Re-optimization of the point design at
the NIF scale is considered, taking into account non-scalable physics and specific
features of the NIF. These results provide a basis for scaling future performance on
OMEGA to performance on the NIF, should a magnetic-field capability and a preheating
beamline be added.
*The information, data, or work presented herein was funded in part by the Advanced
Research Projects Agency-Energy (ARPA-E), U.S. Department of Energy, under Award
Number DE-AR0000568. The views and opinions of authors expressed herein do not
necessarily state or reflect those of the United States Government or any agency thereof.
This material is also based upon work supported by the Department of Energy National
Nuclear Security Administration under Award Number DE-NA0001944; the University
of Rochester; and the New York State Energy Research and Development Authority. The
this paper.
1
S. A. Slutz et al., Phys. Plasmas 17, 056303 (2010).
62
Old Saybrook, CT
May 1-6, 2016
Progress and Plans for Improving Laser Preheating in
MagLIF*
K. J. Peterson, D. H. Barnak2, E. M. Campbell2, P.-Y. Chang2, J. R. Davies2, M.
Geissel, C. S. Goyon2, B. Hansen, A. J. Harvey-Thompson, C. A. Jennings, B. G.
Logan, J. Moody3, T. N. Nagayama, B. B. Pollock2, J. L. Porter, A. B. Sefkow, I. C.
Smith, D. Strozzi3, M.-S. Wei1
Sandia National Laboratories, Albuquerque, New Mexico, 87185
[email protected]
1
General Atomics, San Diego, California, 94550
2
Laboratory for Laser Energetics, Rochester, New York, 14623
3
Lawrence Livermore National Laboratories, Livermore, California, 94550
The magnetized liner inertial fusion (MagLIF) concept is a promising approach to
achieving large fusion yields on the Z facility1,2 that implodes a pre-magnetized (Bz=1030 T) and preheated (~100-200eV) plasma. The first tests of integrated MagLIF
experiments have demonstrated DD neutron yields as high as 2e12 and plasma
temperatures of 3-4keV3. While the initial results are promising, difficult challenges
remain. One prevailing hypothesis of these first experiments, supported by simulations
and several laser heating tests is that only a small fraction of the available laser energy
(2.5kJ) was actually coupled to the fuel. In order to increase the performance of a
MagLIF target, the amount of energy coupled to the fuel from the preheating laser needs
to be increased. It is also critical that the increased energy deposition be done in such a
way to minimize contaminant sources during the preheating phase since these
contaminants can cause unacceptable radiation losses to occur over the ~50ns of a
MagLIF implosion. Thus far, tests of increased laser preheat have led to poorer
performance. Clearly significant uncertainties remain in our understanding of the initial
plasma conditions of a preheated MagLIF target. Laser heating experiments are
currently being performed at Z, OMEGA-EP, OMEGA, and NIF in order to better
understand and characterize the initial conditions of a laser preheated plasma. This talk
will discuss the scientific goals of the experiments being performed at each of these
facilities, the progress in our understanding of preheating MagLIF targets with laser
energy deposition, and the implications for MagLIF target design.
* Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed
Martin Company, for the National Nuclear Security Administration under Contract No.
DE-AC04-94AL85000. Support provided in part by the Laboratory Directed Research
and Development Project No. 173190.
S. A. Slutz, M. C. Herrmann, R. A. Vesey, A. B. Sefkow, et. al., “Pulsed-power-driven cylindrical liner
A. B. Sefkow, S. A. Slutz, J. M. Koning, M. M. Marinak, et. al., “Design of magnetized liner inertial
fusion experiments using the Z facility”, submitted to Phys. Plasmas (2014).
3
M. R. Gomez, S. A. Slutz, A. B. Sefkow, D. B. Sinars, et. al., “Experimental demonstration of fusionrelevant conditions in magnetized liner inertial fusion”, submitted to Phys. Rev. Lett. (2014).
1
2
63
R1-3
R1-4
Old Saybrook, CT
May 1-6, 2016
Modeling Laser-Plasma Interactions in MagLIF
Experiment on NIF*
D. J. Strozzi, R. L. Berger, A. B. Sefkow†, S. H. Langer, T. Chapman,
C. Goyon, B. Pollock, J. D. Moody
7000 East Ave.
Livermore, CA 94550
[email protected]
†
Albuquerque, New Mexico 87185, USA
The MagLIF fusion concept1 achieves fusion energy gain by compressing cryogenic fuel
with a cylindrical, current-carrying metal liner. The scheme requires the fuel to be preheated and embedded in an axial magnetic field. The leading pre-heat scheme is a ~10 ns
laser pulse. A NIF experiment (shot N160128-002) successfully demonstrated laser
propagation at the scale of a fusion-gain design. A plastic “gas pipe” filled with
neopentane (C5H12) was fielded at room temperature and illuminated from one end by a
13 ns pulse from one laser quad, with peak power of 3 TW and focused intensity of
1.6x1014 W/cm2. The measured backscatter was very low, with Raman scattering
reflectivity ≤ 1%, and a burst of Brillouin scattering with reflectivity ~10% when the
laser burned through the tantalum witness plane at the far end of the tube.
We modeled laser-plasma interactions on this shot using linear gain-exponent
calculations2, and the paraxial envelope propagation code pF3D3. These utilized plasma
conditions from simulations by the radiation-hydrodynamics code HYDRA. The Raman
and Brillouin gain spectra, and reflectivity levels from pF3D, will be compared with the
measurements. The role of laser filamentation will also be discussed.
1
S. A. Slutz and R. A. Vasey, “High-Gain Magnetized Inertial Fusion,” Phys. Rev. Lett. 108, 025003
(2012).
2
D. J. Strozzi, E. A. Williams, D. E. Hinkel, D. H. Froula, R. A. London, and D. A. Callahan, “Ray-based
calculations of backscatter in laser fusion targets,” Phys. Plasmas 15, 102703 (2008).
3
R. L. Berger, C. H. Still, E. A. Williams, and A. B. Langdon, “On the dominant and subdominant
behavior of stimulated Raman and Brillouin scattering driven by nonuniform laser beams,” Phys. Plasmas
5, 4337 (1998).
64
Old Saybrook, CT
May 1-6, 2016
Laser propagation through full-scale, high-gain
MagLIF gas pipes using the NIF*
B. B. Pollock, A. B. Sefkow†, C. Goyon, D. Strozzi, S. Khan, M. Rosen, B. G. Logan†,
E. M. Campbell‡, K. J. Peterson†, and J. D. Moody
7000 East Ave.
Livermore, CA 94550
[email protected]
†
‡
Laboratory for Laser Energetics
Rochester, NY 14623
The first relevant measurements of laser propagation through surrogate high-gain
MagLIF gas pipe targets at full scale 1,2 have been performed at the NIF, using 30 kJ of
laser drive from one quad in a 10 ns pulse at an intensity of 2e14 W/cm2. The
unmagnetized pipe is filled with 1 atm of 99%/1% neopentane/Ar, and uses an entrance
window of 0.75 µm polyimide and an exit window of 0.3 µm of Ta backed with 5 µm of
polyimide. Side-on x-ray emission from the plasma is imaged through the 100 µm-thick
epoxy wall onto a framing camera at four times during the drive, and is in excellent
agreement with pre-shot HYDRA radiation-hydrodynamics modeling. X-ray emission
from the Ta exit plane is imaged onto a streak camera to determine the timing and
intensity of the laser burning through the pipe, and the Ar emission from the center of the
pipe is spectrally- and temporally-resolved to determine the plasma electron temperature.
Backscatter is measured throughout the laser drive, and is found to be of significance
only when the laser reaches the Ta exit plane and produces SBS. These first results in
unmagnetized surrogate gas fills are encouraging since they demonstrate sufficient laser
energy absorption and low LPI losses within high-density long-scale-length plasmas for
proposed high-gain MagLIF target designs. We will discuss plans to magnetize targets
filled with high-density DT gas in future experiments.
*This work performed under the auspices of the U.S. Department of Energy by Lawrence
Livermore National Laboratory under Contract DE-AC52-07NA27344. Sandia is a
multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company,
for the National Nuclear Security Administration under Contract No. DE-AC0494AL85000.
1
2
S. A. Slutz and R. A. Vesey, Phys. Rev. Lett. 108, 025003 (2012).
A. B. Sefkow, et. al., Phys. Plasmas 21, 072711 (2014).
65
R2-1
R2-2
Old Saybrook, CT
May 1-6, 2016
A systematic investigation of MagLIF preheat on
OMEGA-EP
A. J. Harvey-Thompson, A. B. Sefkow, M.-S. Wei†, T. N. Nagayama, E. M.
Campbell*, K. Peterson, V. Y. Glebov*, C. Stoeckl*, P.-Y. Chang*, J. R. Davies*,
D. H. Barnak* and R. F. Heeter#
Albuquerque, New Mexico, 87185
[email protected]
†
General Atomics
San Diego, California, 94550
*
Rochester, New York, 14623
#
Lawrence Livermore National Laboratories
The MAGnetized Liner Inertial Fusion (MagLIF) scheme has achieved thermonuclear
fusion yields on the Z Facility1,2 by imploding a cylindrical liner filled with D2 fuel that is
preheated with a 0.53 μm multi-kJ laser and pre-magnetized with an axial Bz=10 T
magnetic field. Preheating (Te = 100-200 eV) and pre-magnetizing (10-30 T) the fuel
serves to reduce the implosion velocity (~107 cm/sec) required to achieve multi-keV
fusion-relevant temperatures at stagnation with modest radial convergence (~20).
Preheating the fuel requires coupling multiple-kJ of optical laser energy at modest
intensities (Iλ2 ~1014 watts-μm2 /cm2) into long scale-length (L~10 mm) D2 plasmas with
initial fuel densities ne/ncrit= 0.05-0.1. The low temperatures (Te<1 keV) and long scale
lengths present during preheat may lead to the growth of laser plasma instabilities (LPI),
and the applied magnetic field suppresses electron thermal conduction which needs to be
accounted for in modeling.
In this talk, we present data and analyses of experiments conducted at the 0.35 μm
OMEGA-EP laser facility investigating the laser preheat of plasmas at MagLIF-relevant
conditions. The experiments vary parameters of interest such as such as laser duration
and power, temporal pulse-shape, beam conditioning, plasma density and laser entrance
hole (LEH) design. We will discuss the experimental findings and their implications on
MagLIF preheat design and compare experimental results to HYDRA simulations.
1
M. R. Gomez et al., “Experimental Demonstration of Fusion-Relevant Conditions in Magnetized Liner
Inertial Fusion,” Phys. Rev. Lett. 113, 155003 (2014).
2
A. B Sefkow et al., “Design of magnetized liner inertial fusion experiments using the Z facility,” Phys.
Plasmas 21, 072711 (2014)
66
46th Annual Anomalous Absorption Conference Old Saybrook, CT May 1-‐6, 2016 Temperature analysis of MagLIF preheat experiments
at OMEGA-EP
T. N. Nagayama, A. J. Harvey-Thompson, A. B. Sefkow, M.-S. Wei†, E. M.
Campbell*, K. Peterson, V. Y. Glebov*, C. Stoeckl*, P.-Y. Chang*, J. R. Davies*, D.
H. Barnak* and R. F. Heeter#
Albuquerque, New Mexico, 87185
[email protected]
†
General Atomics
San Diego, California, 94550
*
Rochester, New York, 14623
#
Lawrence Livermore National Laboratories
Initial integrated experiments for magnetized liner inertial fusion (MagLIF) at
Sandia National Laboratories Z facility achieved thermonuclear fusion yields. D2 fuel
contained in a cylindrical Be shell (i.e., liner) was imploded with a 20-MA current. Prior
to the implosion, the fuel is axially magnetized to Bz=10T and preheated to a few 100 eV
with the Z-Beamlet laser (527 nm). The preheating and magnetization can relax some of
the challenging ignition criteria and play key roles in MagLIF. The preheating allows the
fuel to reach an ignition-relevant temperature with a slower implosion velocity. The axial
magnetization helps to suppress radial thermal conduction losses for efficient fuel heating
and radially traps charged fusion products for self-heating at lower areal densities. The
initial integrated experiments show that many traditional performance requirements are
significantly eased, but also showed significant disagreement with simulations.
To improve MagLIF performance, it is critical to refine our understanding of the
laser-preheat phase. MagLIF plasma is in the regime intermediate to tokamaks and
traditional laser-driven ICF plasmas, and the benchmark experiments in this regime are
limited. We performed a series of MagLIF-relevant laser-preheat experiments at
OMEGA-EP. We mix small amount of Ar into D2 fuel and measure axially resolved Ar
spectra with a time- and spatially-resolved elliptical crystal spectrometer (MSPEC). We
discuss quantitative analysis of results and diagnostic challenges.
67
R2-3
R2-4
68
Old Saybrook, CT
May 1-6, 2016
Laser upgrades at the Sandia’s Z-Backlighter facility in
order to accommodate new requirements for Magnetic
Liner Inertial Fusion on the Z-Machine*
Jens Schwarz, Patrick Rambo, Darrell Armstrong, Ian Smith,
Jonathan Shores, Marius Schollmeier, and John Porter
P.O. Box 5800 MS 1193
Albuquerque, NM 87185-1193
[email protected]
The Z-Backlighter laser facility primarily consists of two high energy, high power laser
systems. Z-Beamlet (ZBL) is a multi-kJ class, nanosecond laser operating at 1054nm
which is frequency doubled to 527nm in order to provide x-ray backlighting of high
energy density events on the Z-Machine. Z-Petawatt (ZPW) is a petawatt-class system
operating at 1054nm delivering up to 500J in 1ps for backlighting and various short pulse
laser experiments.
With the development of the Magnetic Liner Inertial Fusion (MagLIF) concept on the ZMachine, the primary backlighting missions of Z-Beamlet and Z-Petawatt have been
adjusted accordingly. As a result, we have focused our recent efforts on increasing the
output energy of Z-Beamlet from 2 to 4 kJ at 527nm by modifying the fiber front end to
now include extra bandwidth (for SBS suppression). The MagLIF concept requires a
well-defined/behaved beam for interaction with the pressurized fuel. Hence we have
made great efforts to implement an adaptive optics system on Z-Beamlet and have
explored the use of phase plates as well as other novel beam smoothing techniques.
We are also exploring concepts to use Z-Petawatt as a backlighter for Z-Beamlet driven
MagLIF experiments. Alternatively, Z-Petawatt could be used as an additional fusion
fuel pre-heater or as a temporally flexible high energy pre-pulse. All of these concepts
require the ability to operate the Petawatt laser in a ns long-pulse mode (which requires a
substantial modification of the front end), in which the beam can co-propagate with ZBeamlet and can also be focused with a lens. Some of the proposed modifications are
complete and most of them are well on their way. This talk will give a detailed summary
of these efforts.
* Sandia National Laboratories is a multi-program laboratory managed and operated by
Sandia Corporation, wholly owned subsidiary of Lockheed Martin
Corporation, for the U.S. Department of Energy’s National Nuclear Security
Administration under contract DE-AC04-94AL85000.
69
R2-5
70
Old Saybrook, CT
May 1-6, 2016
F1-1
Implementing a Xenon gas soft x-ray shield to prevent
optical “blanking” of the first collection optic of the new
NIF Optical Thomson Scattering Diagnostic*
G.F. Swadling, J.S. Ross, D. Manha, J. Galbraith, P. Datte, J. Kilkenny, O. Landen, J. D.
Moody
Lawrence Livermore National Laboratory,
7000 East Avenue,
Livermore, California
[email protected]
A new optical Thomson scattering (OTS) diagnostic is currently under development at
Lawrence Livermore National Laboratories Laboratory (LLNL). This diagnostic is
designed to measure the plasma parameters in High Energy Density (HED) plasmas
produced in National Ignition Facility (NIF) experiments. The OTS diagnostic has the
potential to radically improve our understanding of these plasmas by providing both
spatially and temporally resolved measurements of the key plasma parameters such as
electron and ion density, temperature, and flow velocity.
X-ray flux induced optical opacity (“blanking”) of the OTS blast shield has been
identified as a potential risk for this diagnostic. In NIF experiments this blast shield will
be situated 60 cm from the hohlraum and as such will be subjected to soft X-ray flux
loads of ~1.5GWcm-2, with a total integrated flux of 8 Jcm-2 over the duration of the
experiment. Our current understanding of “blanking” is quite limited. Experiments at the
OMEGA laser facility have now been designed to improve our understanding of when
the onset of blanking is likely to be observed, and also to test a scheme to mitigate this
effect. A Xenon gas “shield” has been designed, which will act to absorb the x-ray flux
over depth, protecting the blast shield from the X-ray flux while keeping the electron
density of the photo-ionized shield plasma well below the critical density for the scattered
Optical Thomson signal. We will discuss the expected parameters of the photo-ionized
shield plasma and present the results of OMEGA experiments and an analysis of their
implications for OTS on the NIF.
* This work performed under the auspices of the U.S. Department of Energy by
Friday
71
F1-2
Old Saybrook, CT
May 1-6, 2016
Modeling of Neutron Scattering in ICF experiments
Brian D. Appelbe, F. Manke and J. P. Chittenden
Centre for Inertial Fusion Studies
Blackett Laboratory
Imperial College
London, SW7 2AZ, United Kingdom
[email protected]
A significant fraction of the neutrons produced by fusion reactions in ICF experiments
can scatter from the DT fuel and the ablator material. These scattered neutrons are an
important diagnostic of the conditions occurring in the plasma during stagnation. The
energy spectrum of scattered neutrons is used to infer the ρR of the plasma while images
of scattered neutrons reveal the shape of the dense fuel at stagnation. However, a precise
interpretation of these diagnostics is challenging due to the sensitivity of neutron
scattering on the spatial and temporal distribution of hot (neutron emitting) and cold
(neutron scattering) DT fuel. In this work we describe computational models that we have
developed to study the neutron scattering process in ICF experiments and outline some of
the results obtained.
The radiation-hydrodynamics code CHIMERA is used to simulate indirect-drive highfoot implosions in both 1D and 3D. At a number of discrete times during the stagnation
phase, the density, temperatures and velocities occurring in the simulation are postprocessed using a novel neutron transport algorithm. This algorithm uses an inverse
raytrace method in which rays (representing neutron trajectories) are traced backwards
through the simulation domain from a specified neutron detector location to the birth
locations of neutrons. Neutron scattering events cause these rays to change direction. By
assuming that each neutron undergoes only a few scattering events, this algorithm allows
synthetic scattered neutron diagnostics to be produced in a fast and efficient manner.
These computational tools are used to study the effect of both low-mode and multi-mode
implosion asymmetries on scattered neutron diagnostics. It is shown that scattered
neutron images depend not only on the density of cold fuel but also on the proximity of
cold fuel to hot fuel, particularly in multi-mode perturbations. It is also shown that, for
low-mode perturbations, there can be large variations in the fuel ρR along different linesof-sight. However, the synthetic neutron down-scattered ratio (DSR – the ratio of primary
DT (13-15 MeV) neutrons to scattered (10-12 MeV) neutrons) measured along the same
lines-of-sight is almost isotropic.
72
Old Saybrook, CT
May 1-6, 2016
Characterization of hot electron coupling in shock
ignition-relevant regimes*
Christine M. Krauland, S. Zhang, J. Peebles, F. N. Beg, N. Alexander†, W. Theobald!, R.
Betti!, D. Haberberger!, C. Ren!, R. Yan!, E. Borwick!, M. Campbell!,
and M. S. Wei†
Center for Energy Research, University of California – San Diego
La Jolla, CA 92093
[email protected]
†
Inertial Fusion Technology, General Atomics
San Diego, CA 92121
!
Laboratory for Laser Energetic, University of Rochester
Rochester, NY 14623
An alternative high gain laser fusion scheme known as shock ignition1 (SI) proposes the
launch of a spherically converging ignitor shock in the latest stage of fuel assembly by a
short ‘spike’ pulse with ~5×1015 Wcm-2 absorbed intensity. As a result of this high
intensity pulse interacting with a long scalelength plasma, nonlinear laser plasma
instabilities (LPI) and hot electrons become critical issues. In recent OMEGA-60
experiments2, it has been suggested that <100 keV electrons could be beneficial to SI by
augmenting ablation pressure and ultimately leading to gigabar-level shocks.
Here we present new experiments using the high energy OMEGA EP laser
system to examine the effect of laser wavelength, intensity and plasma conditions on hot
electron generation and energy coupling in SI-relevant regimes in a planar geometry.
Two UV beams (~6.25 kJ, 3.5×1014 Wcm-2) are initially employed to produce a long
scalelength hot (~keV) plasma by irradiating the ablator of a multilayered foil target.
These are followed by the main higher intensity interaction pulse, which is either a kJ 1ns UV pulse with intensity ~1.6×1016 Wcm-2 or a kJ 0.1-ns IR pulse with intensity up to
2×1017 Wcm-2 at varying time delays. Our results demonstrate IR beam energy coupling
to the target after propagating over ~0.5 mm long scalelength plasma. This beam was
observed to break into many filaments near the quarter critical density region of the
plasma and propagated to the critical density without merging, producing hot electrons
with temperature of ~70 keV in a well-contained beam, suitable for electron-assisted SI.
Details of the experiments and particle-in-cell simulations will be presented.
*This work conducted under the auspices of the U.S. Department of Energy under
contracts DE-NA0002730 (NLUF) and DE-SC0014666 (HEDLP).
R. Betti et al., “Shock Ignition of Thermonuclear Fuel with High Areal Density”, Physical Review Letters
98, 155001 (2007).
2
W. Theobald et al., “Spherical Strong-Shock Generation for Shock-Ignition Inertial Fusion”, Physics of
Plasmas. 22, 056310 (2015).
1
73
F1-3
F1-4
Old Saybrook, CT
May 1-6, 2016
Scaled laboratory experiments explain the kink
behavior of the Crab Nebula jet
C. K. Li1, P. Tzeferacos2, D. Lamb2, M. J. Rosenberg1, R. K. Follett3, D. H. Froula3,4, M.
Koenig5, F. H. Seguin1, J. A. Frenje1, H. G. Rinderknecht1, H. Sio1, A. B. Zylstra1,
R. D. Petrasso1, P. A. Amendt6, H. S. Park6, B. A. Remington6, D. D. Ryutov6, S.
C. Wilks6, R. Betti3,4, A. Frank3,4, S. X. Hu3, T. C. Sangster3, P. Hartigan7, R. P.
Drake8, C. C. Kuranz8, G. Gregori9, P. A. Norreys9, S. V. Lebedev10,
and N. C. Woolsey11
1
Plasma Science and Fusion Center, Massachusetts Institute of Technology,
77 Massachusetts Avenue, Cambridge, MA 02139 USA.
2
Department of Astronomy and Astrophysics, University of Chicago,
5640 South Ellis Avenue, Chicago, Illinois, 60637 USA.
3
Laboratory for Laser Energetics, University of Rochester, Rochester,
New York 14627, USA.
4
Department of Physics and Astronomy, University of Rochester, Rochester,
New York 14627, USA
5
Laboratoire LULI, Ecole Polytechnique, 91128 Palaiseau Cedex, France
6
Lawrence Livermore National Laboratory, Livermore, California 94551, USA.
7
Department of Physics and Astronomy, Rice University,
6100 S. Main, Houston, Texas 77521, USA.
8
Department of Atmospheric, Ocean and Space Science, University of Michigan,
2455 Hayward Street, Ann Arbor, Michigan 48103, USA.
9
Department of Physics, University of Oxford, Parks Road, Oxford OX1 3PU, UK.
10
The Blackett Laboratory, Imperial College London, SW7 2BW London, UK.
11
Department of physics, University of York, York YO10 5D, UK.
The remarkable discovery by the Chandra X-Ray Observatory that the Crab nebula’s jet
periodically changes direction provides a challenge to our understanding of astrophysical
jet dynamics. To study the physics of this jet in the laboratory for the first time, we used
high-power lasers to create a plasma jet that could be directly compared with the Crab
nebula jet through well-defined physical scaling laws. This jet generated its own embedded
toroidal magnetic fields; as it moved, plasma instabilities resulted in multiple deflections
of the propagation direction, mimicking the behavior that has been observed in the Crab
jet. In addition, we successfully modeled the experiment with 3-dimensional numerical
simulations that show exactly how instability develops and causes the kinks and resultant
changes of direction in the jet. Unparalleled spatial visualization and quantitative
measurements in this work not only provided the first picture of the magnetic fields and
instabilities associated with a supersonic jet, and advanced our knowledge of the structure
and dynamics of the Crab jet, but also opened up tremendous opportunities for laboratory
study of jets from a variety of other astrophysical objects. We expect that future work along
this line will have important impact on the study and understanding of fundamental
astrophysical phenomena.
74
Old Saybrook, CT
May 1-6, 2016
Plasma diffusion across coupling regimes*
Grigory Kagan, J. Daligault,† and S. D. Baalrud
P.O. Box 1663, Los Alamos, NM 87545
[email protected]
†
Department of Physics and Astronomy, University of Iowa
Iowa City, IA 52242
Most HEDP plasmas contain multiple ion species and the relative concentrations of these
species can change over time. To understand the physics behind the evolution of the
concentrations, the inter-ion-species diffusion needs to be evaluated. While prescriptions
for such transport calculations exist for conventional, or weakly coupled, plasmas, the
case of finite coupling is comparatively less well explored. The classical diffusion was
considered in some specific cases with molecular dynamics (MD) simulations. Given the
classical diffusion coefficient, baro- and electro-diffusions can be evaluated with solely
thermodynamic means without invoking further kinetic analysis. The role of thermosdiffusion, on the other hand, remains poorly understood. The conventional theory of
neutral gas mixtures finds that it is usually much lower than baro-diffusion, whereas the
recent study revealed that in weakly coupled plasmas it is generally as large as, or even
dominate over, baro-diffusion.
We investigate the inter-ion-species diffusion in weakly to strongly coupled plasmas with
the help of the recently proposed effective potential theory (EPT). This framework
incorporates many-body correlation effects that arise at moderate coupling by replacing
the Debye Coulomb potential with the potential of mean force in the evaluation of a
binary scattering cross section. Combining this idea with the well-established transport
techniques for rarefied gases gives the full set of transport coefficients needed for fluid
description of multi-component plasmas across coupling regimes. In particular, we find
that thermo-diffusion is diminished and the dynamic friction coefficient tends to unity in
substantially coupled plasmas.
*This work is performed under the auspices of the U.S. Dept. of Energy by the Los
Alamos National Security, LLC, Los Alamos National Laboratory under Contract No.
DE-AC52-06NA25396.
1
G. Kagan and X. Z, Tang, Phys. Plasmas 19, 082709 (2012).
G. Kagan and X. Z, Tang, Phys. Lett. A 378, 1531 (2014).
3
S. D. Baalrud and J. Daligault, Phys. Rev. Lett. 110, 235001 (2013).
4
J. Daligault, S. D. Baalrud, C. E. Starrett, D. Saumon, and T. Sjostrom, Phys. Rev. Lett. 116, 075002
(2016).
5
G. Kagan, S. D. Baalrud, and J. O. Daligault, “Multi-component Plasma Transport Across Coupling
Regimes,” to be submitted.
2
75
F2-1
Old Saybrook, CT
May 1-6, 2016
F2-2
Experimental signatures of suprathermal ion
distribution in inertial confinement fusion implosions*
Grigory Kagan, D. Svyatskiy, H. G. Rinderknecht†, M. J. Rosenberg‡, A. B. Zylstra,
C.-K. Huang, and C. J. McDevitt
P.O. Box 1663, Los Alamos, NM 87545
[email protected]
†
Livermore, CA 94551
‡
Rochester, NY 14623
The distribution function of suprathermal ions is found to be self-similar under conditions
relevant to inertial confinement fusion hot-spots. By utilizing this feature, interference
between the hydro-instabilities and kinetic effects is for the first time assessed
quantitatively to find that the instabilities substantially aggravate the fusion reactivity
reduction. The ion tail depletion is also shown to lower the experimentally inferred ion
temperature, a novel kinetic effect that may explain the discrepancy between the
exploding pusher experiments and rad-hydro simulations and contribute to the
observation that temperature inferred from DD reaction products is lower than from DT
at National Ignition Facility.
*This work is performed under the auspices of the U.S. Dept. of Energy by the Los
Alamos National Security, LLC, Los Alamos National Laboratory under Contract No.
DE-AC52-06NA25396.
1
G. Kagan G. Svyatskiy, H. Rinderknecht, M. Rosenberg, A. Zylstra, C.-K. Huang, and C. McDevitt, Phys.
Rev. Lett. 115, 105002 (2015).
76
Old Saybrook, CT
May 1-6, 2016
Probing kinetic and multi-ion-fluid effects in ICF
plasmas using precision time-resolved measurements of
several nuclear reactions, and x-ray core continuum at
OMEGA*
H. W. Sio1, J. A. Frenje1, J. Katz2, H. G. Rinderknecht3, M. Gatu Johnson1, F. H. Seguin1,
C. K. Li1, R. D. Petrasso1, C. Stoeckl2, D. Weiner2, T. Kwan4, A. Le4, W. Taitano4, A.
Simakov4, L. Chacon4, C. Sorce2, S. Regan2, and T. C. Sangster2
1
Massachusetts Institute of Technology Plasma Science and Fusion Center, Cambridge, MA
02139, USA
3
Laboratory for Laser Energetics, University of Rochester, Rochester, NY 14623, USA
3
Lawrence Livermore National Laboratory, Livermore, CA 94550, USA
4
Los Alamos National Laboratory, Los Alamos, NM 87544, USA
[email protected]
To explore kinetic and multi-ion-fluid effects produced in High Energy Density Plasmas (HEDP)
and Inertial Confinement Fusion (ICF) implosions at OMEGA, several nuclear reactions and xray core emission histories were measured with one diagnostic, i.e., the Particle X-ray Temporal
Diagnostic (PXTD). These time-resolved precision measurements of the nuclear reactions and
the x-ray core continuum using PXTD, from which Ti(t) and Te(t) are inferred, enable quantitative
assessments of kinetic effects, multi-ion-fluid effects, and i-e equilibration rates during the shockburn phase. Understanding i-e equilibration rates in HEDP at various conditions will also enable
us, for the first time, to experimentally determine the Coulomb Logarithm. The observed
differences between the nuclear reaction histories are contrasted to 1-D single-ion-fluid, multipleion-fluids, and kinetic-ion simulations for different gas-fill pressure and gas mixture. *This work
was supported in part by the U.S. DOE, LLE, LLNL, and DOE NNSA SSGF.
77
F2-3
Old Saybrook, CT
May 1-6, 2016
F2-4
Detection of interspecies ion separation via analysis of
spatially resolved x-ray spectra in OMEGA implosions*
T. Joshi, P. Hakel, S. C. Hsu, M. Schmitt, E. Vold, R. Rauenzahn, Y. Kim, G. Kagan,
H. Herrmann, X.-Z. Tang, and N. Hoffman
Los Alamos National Laboratory, P.O. Box 1663, Los Alamos, NM 87545
[email protected]
We have experimentally inferred interspecies ion separation by analyzing spectrally resolved Xray images from OMEGA direct-drive ICF implosions. The targets were spherical plastic shells
of either 13-μm shell thickness and 5-atm D2/Ar gas fill or 15-μm shell thickness and 3-atm
D2/Ar gas fill. For each thickness/fill combination, we had both 1.0% and 0.1% Ar by atom
fraction, of which the cases with 1.0% Ar yielded line emissions suitable for our analysis. This
campaign design was guided by the fact that interspecies thermo-diffusion forces1 would be
strongest for species with large mass difference, hence the focus on D2/Ar fill. Our implosions
were deliberately designed to be in a more-collisional regime (as opposed to the more-kinetic
regime of exploding pushers) to validate the theory. Argon K-shell spectral features are observed
primarily between the time of first-shock convergence and slightly before neutron bang time,
using a time- and space- integrated spectrometer (XRS2), streaked crystal spectrometer (SSCA),
and two gated multi- monochromatic X-ray imagers (MMI) fielded along quasi-orthogonal linesof-sight. The spectrally resolved MMI data were processed to obtain narrowband images2 and
spatially resolved spectra for annular regions at different radii of each image.3 An emissivityanalysis4 method is used to extract electron temperature and density spatial profiles in the
implosion core. A narrowband-image method and a complementary analysis5 method of the
spatially resolved Ar X-ray lines both reveal deviation from the initial spatially uniform, 1% Ar
concentration in the core, thus providing direct proof of interspecies ion separation between the
Ar and D. Both Ar- concentration enhancement (to several percent) and depletion (to a small
fraction of 1%) are observed for different times and radial positions of the implosion; we are in
the process of refining these results and in quantifying the error bars. Experimental results are
compared against the predictions of HYDRA and RAGE post-shot modeling. The RAGE
simulations explicitly model the interspecies Ar/D-diffusion dynamics based on the two-ionspecies transport model of Molvig et al6. Other radiation-hydrodynamic simulations employ an
N-species moment-based transport model owing to Zimmerman, Paquette7, Kagan1, and
Zhdanov8, in which all N x (N-1) species interactions are accounted for individually, representing
a significant improvement beyond an earlier mean-background model9. *This work was
supported by the LANL ICF Program under U.S. DoE Contract No. DE-AC52-06NA25396.
1
G. Kagan and X.-Z. Tang, Phys. Lett. A 378, 1531 (2014).
T. Nagayama, et al, J. App. Phys. 109, 093303 (2011).
3
T. Nagayama, et al, Phys. Plasmas 21, 050702 (2014).
4
L. Welser-Sherrill, et al, Phys. Rev. E 76, 056403 (2007).
5
T. Joshi, Ph. D. Dissertation, University of Nevada, Reno (2015).
6
K. Molvig, A. N. Simakov, and E. L. Vold, Phys. Plasmas 21, 092709 (2014).
7
C. Paquette et al., Ap. J. Supp. 61, 177 (1986)
8
V. M. Zhdanov, Transport Processes in Multicomponent Plasma, Taylor and Francis, New York, 2002.
9
N. Hoffman, G. Zimmerman, et al., Phys. Plasmas 22, 052707 (2015).
78
2
Old Saybrook, CT
May 1-6, 2016
Visualization of hohlraum-wall motion at the National
Ignition Facility*
Presenter N. Izumi, G. N. Hall, M. A. Barrios, N. Meezan, O. Jones, O. L. Landen,
J. J. Kroll, S. Vonhof, A. Nikroo, J. Jaquez†, C Bailey, M. Hardy, R, Ehrlich,
R. Pj. Town, D. Bradley, D. E. Hinkel, J. D. Moody
7000 East Avenue
Livermore, CA 94551
[email protected]
†
General Atomics
San Diego, CA 92121
The high fuel capsule compression required for indirect drive inertial confinement fusion
(ICF) requires careful control of the x-ray drive symmetry throughout the laser drive.
When the outer cone beams strike the hohlraum wall, the plasma ablated off the
hohlraum wall expands into the hohlraum and may impede propagation of the inner cone
beams. This dynamic effect alters the x-ray drive symmetry especially at the final stage
of the drive pulse. To quantitatively understand the wall motion, we developed a new
platform which visualizes the expansion and stagnation of the hohlraum wall plasma.
We utilized existing ¾ length hohlraums with a plastic (CH) capsule. The location on the
hohlraum wall corresponding to the laser spot of quad 34B and quad 13B was coated
with a 320 nm layer of cobalt. The capsule surface was coated with a 320 nm layer of
manganese. Expansion of these tracers is visualized by imaging 6.2 keV and 7.2 keV line
emission by using a Ross filter pair coupled with an x-ray framing camera. Dynamic
expansion and stagnation of the hohlraum wall was visualized successfully with this
technique.
We report the details of the experiment and the comparison to radiation-hydro
simulations.
* Prepared by LLNL under Contract DE-AC52-07NA27344.
79
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2016 Anomalous Absorption Abstract Booklet - Meetings

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