25th IAEA FEC , St. Petersburg, Russia 13th

Transcription

Compatibility of high
performance scenarios
with ILW
I. Nunes
JET Culham Science Centre
Abingdon, OX14 3DB, UK
I Nunes 1 (20)
25th IAEA FEC , St. Petersburg, Russia
13th -18th October 2014
I Nunes1, I Balboa2, M Baruzzo3, C Challis2, P Drewelow4, L Frassinetti5,
D Frigione3, J Garcia6, J Hobirk7, E Joffrin6, P J Lomas2, E de la Luna8, C
Lowry9, F Rimini2, ACC Sips9, S Wiesen10 and the JET contributors*
JET, Culham Science Centre, Abingdon, OX14 3DB, UK
1Instituto
de Plasmas e Fusão Nuclear, IST, Universidade de Lisboa, Portugal
2CCFE, Culham Science Centre, Abingdon, OX14 3DB, UK
3ENEA, Consorzio RFX Padova, Italy
4 Max-Planck-Institut fuer Plasmaphysik, Teilinstitut Greifswald, D-17491, Germany
5VR, Fusion Plasma Physics, EES, KTH, SE-10044 Stockholm, Sweden,
6CEA, IRFM, F-13108 Saint-Paul-lez-Durance, France
7Max-Planck-Institut für Plasmaphysik, D-85748 Garching, Germany
8Laboratorio Nacional de Fusion, CIEMAT,28040, Madrid, Spain
9European Commission, Brussels, Belgium
10Institut fuer Energie-und Klimaforschung, IEK-4, FZJ, TEC, 52425 Julich, Germany
I Nunes 2 (20)
Background
JET-C up to 2009

Mainly unfuelled plasma up to
3.8MA with good confinement
16
Above 3.8MA  high gas dosing to
mitigate 1MJ ELMs
12
JET-ILW 2012
 Development reached 3.5MA,
although reduced confinement
14
2.5MA
3.0MA
3.5MA
3.8MA
4.0MA
4.25MA
4.5MA
CFC 2009
8
6
4
Aim JET-ILW 2014
2
 Recover confinement
0
ILW 2012
2.5MA
0
 Achieve 4MA
I Nunes 3 (20)
2.2MA
10
Wth (MJ)

2
4
2.7MA
3.0MA
6
8
10
W98y,2 (MJ)
3.25MA
12
3.5MA
14
16
Outline
 Scenario choices/strategies
 Integration into the scenario of:
 Control of W core accumulation
 Divertor heat load control
 Confinement
 Summary and future prospects
I Nunes 4 (20)
Operational limits on JET PFCs
Be limiter
Solid Be limiter
 Surface temperature limit: 900oC
 Heat flux factor: 22 MJm-2s-1/2
V. Riccardo et al. Phys. Scripta 2010
Ph. Mertens et al. J. Nucl. Mater 2013
W-coated
CFC
Bulk W
divertor
I Nunes 5 (20)
20µm W on top
W-coated CFC divertor tiles
 Energy limit: 250 MJ / row
Bulk W divertor
 Heat flux factor: 35 MJm-2s-1/2
 Energy limit: 60 MJm-2 or stack
5
Scenario choices and strategies
4MA H-mode  ~500-700 tones + ~20MJ of energy
Margin of a factor of 2 against serious damage to the vessel
Scenario optimised for

Minimum disruption force – minimise PF currents

Maximum Ip within currents coils constraints 
low triangularity

Maximise q95 for given Ip/BT  large volume

Avoid plasma-wall contact
I Nunes 6 (20)
> 2.5cm
> 4cm
Scenario choices and strategies
Special care
 IP ramp-up  low li to optimise volume
 IP ramp-down (high li) balance between
 fast Ip ramp-down  reduce disruption forces
 Shrink plasma to avoid wall contact 
increase PF  increase disruption forces
> 2.5cm
> 4cm
 Disruption avoidance
 Early detection of off-normal events
 MGI if disruption unavoidable
I Nunes 7 (20)
High-Z impurity accumulation
Most common cause of off-normal event  High-Z impurity accumulation
(50% likely to disrupt)

NBI switch-off

ELM frequency decreases

W concentration in core increases

temperature profiles become hollow
after sawteeth stop

current profile becomes hollow and
an n=1 mode grows until it triggers
the MGI.
 Early detection of radiation peaking
choice of alarm level:
too early vs. too late
work in progress …
I Nunes 8 (20)
Outline
 integration into the scenario of:
 Confinement
I Nunes 9 (20)
Control of W accumulation – gas
Gas puffing
 Increases ELM frequency to control W reaching the plasma core
2.5MA/2.35T
 Stationary discharges although at reduced confinement
#86582
Wth (MJ)
H98(y,2)
#86587
#86534
#86538
#86586
<ne> (1019 m-3)
(1022/s)
16Hz
25Hz
52Hz
68Hz
85Hz
D2 dosing (1021/s)
I Nunes 10 (20)
Control of W accumulation - ICRH

ICRH heating  increases core electron temperature and maintain
sawteeth activity  expel W from core
E Lerche EX/P5-22
RF frequencies
3.0MA
BT constraints
(q95=3)
H minority off-axis
 Effective if resonance inside q=1
surface
He3 minority on-axis
 Similar results to H minority (off-axis,
inside q=1 surface) at ~8% He3
concentration  small impact on
performance
I Nunes 11 (20)
Outline
 Confinement
I Nunes 12 (20)
Divertor heat load control
JET has restrictive operation limits for bulk W and W coated CFC tiles  pulse
length at high power at high plasma current
Extrinsic impurities
 N2 not compatible with DT
operation  Tritium plant at JET
 Ne: Small reduction of target
surface temperature
2.5MA/2.35T
#87404 #87215 #87218
Strike point sweeping at 4Hz
 4cm sweeping  strong reduction
of surface target temperature
I Nunes 13 (20)
Divertor heat load control – Ne
Ne
w/o Ne
Ne + sweep
Ne + sweep
Ne
Sweep w/o Ne

Range of D2/Ne narrow transitions to ELM-free followed by type III ELMs

Small change PradDIV/Prad,TOT with Ne injection observations of small
reduction of target surface temperature

Experiments at 3.5MA show no increase of Prad,div
I Nunes 14 (20)
C Giroud Ex/P5-25
Outline
 Confinement
I Nunes 15 (20)
Confinement (strike point position)


Strike points close to pump throat

operate at lower pedestal density  higher pedestal temperature
As a consequence confinement improves (still need for gas puffing)
cryopump
I Nunes 16 (20)
Pedestal and core behaviour
pedestal


core
Pedestal - Similar pedestal pressure but higher pedestal temperature
when strike points closer to pump throat
Core - higher density peaking due to lower collisionality  higher core
pressure
E de la Luna EX/P5-29
I Nunes 17 (20)
E Joffrin EX/P5-40
C Maggi EX/3-3
Pedestal behaviour for increasing Ip
 JET-C: both Te,ped and ne.ped
increase with Ip
 Density similar to JET-C but Teped,
below ~1.2keV for Ip>2.5MA
 At similar Ip/BT the pedestal
pressure is considerable lower
than that on CFC
 Hybrid scenario shows that
with high Padd is possible to
get higher Te,ped  higher
confinement
I Nunes 18 (20)
Confinement dependence on PIN

H98(y,2) is seen to strongly increase for bN,th above ~1.6 with a fast rise of the
pedestal pressure, mainly due to the increase of the pedestal temperature
C Challis EX/9-3
q95=3

I Nunes 19 (20)
Achievement of good
confinement at high Ip/BT
strongly dependent on power
(and gas dosing)
Summary





Optimised plasma termination
and the detection of off-normal
events
q95=3
Used gas dosing and ICRH to
control W accumulation
Optimised confinement by
increasing pedestal temperature
Achieved H98(y,2)~1 at 2.5MA (like
JET-C)
Achieved stationary conditions
up to 4MA/3.73T (PTOT=27MW)
I Nunes 20 (20)
Prospects
 Further optimisation is a primary
goal for 2015/2016 campaigns
q95=3
 Higher available additional
power 32MW NBI + ~10MW RF
FEC 2016
 Reduce gas dosing
 Explore other extrinsic impurities
for divertor heat load control
 Minimise gas fuelling to improve
confinement by introducing
fuelling with pellets
I Nunes 21 (20)

25th IAEA FEC , St. Petersburg, Russia 13th

Transcription

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