The K600 at iThemba LABS

The K600 Magnetic
Spectrometer
Retief Neveling, iThemba LABS
This talk
●
Introduction to the K600 at iThemba LABS
●
The K600 at 0˚
●
Recent developments
●
Plans for the future
●
Challenges
An introduction
A kinematically corrected QDD magnetic spectrometer for light ions
IUCF design:
Medium Dispersion focal plane:
3 focal planes: low, medium & high dispersion
Large momentum range: pmax/pmin=1.097
Kinematic correction coils: K & H
Resolving power: p/p = 1/28000
Nominal Bending radius: 2.1m
B(max)= 1.64 Tesla
Horizontal magnification Mx =-0.52
Vertical magnification My =-5.5
Dispersion: 8.4 cm/%
B(D1)=B(D2)
The early 90’s
Today
Focal plane detectors
focal plane detectors: 2 MWDC + 2 scintillators
(2 generations available)
Designed and manufactured
at iThemba LABS
DAQ and electronics
682 wires
40
wires
per event
a few A signal
amplified with Technoland preamp A/D cards
TDC: 100 pico second resolution
Old CAMAC electronics
DAQ: PSI MIDAS
Data rates: Up to 2kHz or 0.5MB/sec
Flexible, scalable
QDC: 0.2 pico Coulomb resolution
Scintillators
4PMT
VME electronics
The K600 at 0°
(p,p') setup: B(D1)/B(D2)=1.5
(p,t) setup: B(D1)/B(D2) = 1
beam of 1 nA:6x109 particels/sec
scattered particles:103 particels/sec
iThemba LABS cyclotron facility
(p,p') at 0°
Accelerators up to object slit 9X:
Single turn extraction (SPC2, SSC)
100 (200) MeV proton SSC transmission eff: 95% (60%)
Object size (1 x 2mm2) determined by XY slit 9X
Faint beam:
High energy beamline:
Double dispersive mode;
2 monochromators in mirror symmetry
Good transmission efficiency; halo clean-up slits
Emmittance: 5-6  mm rad (X)
1-2  mm rad (Y)
Dispersion matching:
Faint beam method: 200 MeV: 22 keV (FWHM)
(p,p') at 0° : beam halo
Object defined by XY slit 9X
Transmission: SSC extraction to target
• 100 MeV: 80%
• 200 MeV: 8%
Halo tuning starts at several kHz
• optimized at <100 Hz/nA
• best: 34 Hz @ 1.4 nA
trigger
ci
Iterative Procedure:
achieve low beam halo
faint beam dispersion
matching
(p,p') at 0° : beam halo
Bergoz Beam Loss Monitor
(p,p') at 0° : beam halo
(gated)
Empty target frame:
100 Hz @ 1nA
Y(FP)
trigger
Scint 1
TOF
Scint 1
X(FP)
TOF
X(FP)
Scint 2
(p,p') at 0° : empty vs target
Scint 1
Al target, 300 Hz @ 1nA
TOF
Scint 1
27
TOF
X(FP)
Scint 2
(p,p') at 0° : target related background
Small angle elastic scattering, re-scattering from
collimator edge, K600 vacuum chamber
(p,p') at 0° : target related background
Small angle elastic scattering, re-scattering from
collimator edge, K600 vacuum chamber
Not good without collimator
Slit scattering: partially E degraded
through collimator lip
12
C(p,p') @ 200 MeV
(p,p') at 0° : background subtraction
Effective beam halo rate: a few Hz
(p,p') at 0° : background subtraction
Background 1
Data+background
Background 2
40
Ca(p,p’)
Ep=200 MeV
(p,p') at 0°
2010
Good energy resolution obtained: 40Ca(p,p') 50 keV (FWHM)
(p,p') at 0°: Low Ex limit
proton beam
to beamdump
E
x
=0
Me
V
 109 s-1
E
x
=2
4M
eV
Whole focal plane:  103 s-1
(p,p')
0°: Low Ex limit
Low Eat
limit
x
2012
Good energy resolution obtained: faint beam 22 keV (FWHM)
24Mg(p,p') 35 keV (FWHM)
Sn
For Ep=160 MeV we should reach 5 MeV, with full  acceptance from 6 MeV
(p,p')
0°: challenges
Low Eat
limit
x
Signal to noise ratio decrease as target mass increases
40
Ca(p,p’)
96
`
Mo(p,p’)
(p,p') at 0°: beamspot limitation
RCNP: Y on target 0.3mm
iThemba LABS:
25 mm
10 mm
2 mm
13 mm
(p,p') at 0°: off-focus mode limitation
iThemba LABS
Focus mode

RCNP
Slight off-focus mode

Y
Y
(p,p') at 0°: off-focus mode limitation
iThemba LABS
Slight off-focus mode

RCNP
Slight off-focus mode

Y
Y
(p,p') at 0°: off-focus mode limitation
Ideal off-focus mode
Challenge: angular cuts in 0˚ measurement
Y
Limited by vertical size of the beam on target

Real-life compromise
Y
Y
Xfp
Comparison with RCNP
K600 (high disp f.p.)
Grand Raiden
(x|Δp/p)
10.9 cm/%
15.451 cm/%
(x|x) (θ|θ)
0.74 1.37
0.417 2.4
(y|y) (φ|φ)
7.05 0.13
5.98 0.17
xfp FWHM
0.35 mm (=11keV @ 31keV/mm) 0.29 mm
XY focal plane
Cross with large angle
Almost parallel
Small angle mode
Presently there is a blind-spot
between 2° and 5°
Low L excitation modes require
measurements at these presently
unreachable angles (M2 twist mode,
but E1/M1 and ISGQR studies would
also benefit)
A new forward-angle mode of the
spectrometer must be developed
Likely to be as sensitive to beam
halo as 0°
(p,t)
at
0°
The
K600
at
0°
TRACK
(p,t)
at
0°
The
K600
at
0°
TRACK
(p,t) at 0°
Large R difference between beam and t
Clear PID
No collimator ⇒ full acceptance 2.51
No background ⇒ overfocus mode
40
Q
D1
D2
Q
D1
D2
Ca(p,t) @ 100 MeV
Focal plane
target
Angle reconstruction possible
(p,t) at 0°
High precision measurements
of the rp-process
Ebeam=100 MeV
E (fwhm) = 32 keV
scat (fwhm) = 0.6˚
22
Ne+mylar(p,t)
12
C(p,t)
Search for 0+ cluster state near
the 5  breakup threshold in 20Ne
Ebeam= 60 MeV
E (fwhm) = 40-50 keV
The K600 and ancillary detectors
At 0°: enhance particular states and
observe their particle decay
Si-strip detectors:
K600 + 136 ADC channels
(October 2012)
New capabilities: (,´)
gs 0+
2011: Semester 1
C(α,α') at 200 MeV
8°-9°
48 keV (FWHM)
12
contaminants
4.438 2+
contaminants
7.654 0+
9.641 3-
H(p,p’)
 is a S=0 T=0 probe
Investigations of S=0 T=0 excitation modes
New capabilities: (,´) ?
K600 @ iThemba LABS
20 keV
Spectroscopy of low-lying E1 strength
through (,')
HPGe
180 keV
Big-Byte @ KVI
NIMA 564 (2006) 267
New capabilities: (,´) ?
K600 @ iThemba LABS
20 keV
E-resolution of  detection ~20 keV
mandatory to uniquely identify 1- states
(PRL 97 (2006) 172502)
HPGe
180 keV
Low(er) energy spectroscopy
No evidence of
2+ state in 12C at 11.16 MeV
Energy resolution: 65 keV FWHM
PRC 3 (1971) 442
PRC 86 (2012) 037301
New focal plane detectors?
●
Sn(p,t) at Ep=50 MeV at 0°
Q=-7.1 MeV
●
Measured down to Et=26 MeV ●
Triggered on 1 scintillator only
lots of background pulse selection
Experimental program limited by energy loss in fp detectors
E.g. (20Ne,α) at 0° beam energy limited to above 65 MeV
d and t @ 40­50 MeV: thinner scintillators, still get coincidence counting
Search for the GPV
PRC83 (2011) 07302
●
120
Low E-resolution study with
achromatic beam: 65 keV resolution
New focal plane detectors?
●
●
120
Sn(p,t) at Ep=50 MeV at 0°
Q=-7.1 MeV
●
Measured down to Et=26 MeV ●
Triggered on 1 scintillator only
lots of background pulse selection
Experimental program limited by energy loss in fp detectors
E.g. (20Ne,α) at 0° beam energy limited to above 65 MeV
d and t @ 40­50 MeV: thinner scintillators, still get coincidence counting
Low E 3He, 4He: replace VDCs with cathode strip detectors (à la Q3D)
ACTAR?
Paul Papka
(University of Stellenbosch) says:
The road ahead
●
(p,p´) @ 0°
smaller y for beamspot at target, improve scat selectivity
active collimator
●
(p,p´) small angle mode
●
(,´) @ 0°
●
(,´) @ 0°
●
New focal plane detector for low energy p,t,d,3He, detection
●
ACTAR
K600
at this workshop
Low Eprojects
limit
x
Maxwell Jingo (Wits U, South Africa): Investigation of fine structure of the IVGDR in nuclei across the periodic table using proton inelastic scattering at 0˚
Lindsay Donaldson (Wits U, South Africa): Fine structure of the IVGDR using the (p,p’) reaction at 0˚: effects of strong nuclear deformation
Alexander Long (U Notre Dame, USA): Exploring the p process with high precision (p,t) reactions
Iyabo Usman (Wits U, South Africa): Overview of experiments on the fine structure of the ISGQR at iThemba LABS
Oscar Kureba (Wits U, South Africa): Effects of nuclear deformation on the fine structure of the ISGQR of even­even Nd isotopes using proton inelastic scattering
Jacobus Swartz (U Stellenbosch, South Africa): Search for the 0+ 5 cluster state in 20Ne
Fhumulani Nemulodi (U Stellenbosch, South Africa): Characterization of the 2+ excitation of the Hoyle State in 12C
The
End
(p,p´)
at
0°
TRACK
The K600 and ancillary detectors
(p,p´)
at
0°
TRACK
Measurements bigger than 21°
Measurements between 7° and 21°
Measurements at 0°
(p,t)
at
0°
The
K600
at
0°
TRACK
Small angle and zero degrees history
Small angle or zero degrees measurements in the 80’s and 90’s
Year Reaction
Lab
Spectrometer
Ebeam
Resolution (FWHM)
1979 (3He,3He') Grenoble ISN -
36.17 MeV/A
few 100 keV
1980 (,')
32.3 MeV/A
few 100 keV
Texas A&M
Enge split pole
Comment
1.85˚
Ref.
PL 84B (1979) 305
PRL 45 (1980) 1670
PRC 31 (1985)1643
1982 (p,p')
Orsay
-
200 MeV
60 keV
1985 (p,p')
Los Alamos
-
-
-
1989 (p,p')
TRIUMF
1991 (7Li,7Be)
RCNP
1991 (p,p')
-
2-3˚
PRC 26 (1982) 87
-
200 MeV
80 keV
3˚
PL B218 (1989) 439
Raiden
26 MeV/A
200 keV
NIMA 302 (1991) 472
RCNP
Raiden
67 MeV
100-200 keV
RCNP AnRep 1991 p6
1993 (p,p')
RCNP
Grand Raiden
100-400 MeV
120 keV
RCNP AnRep 1993 p9
1997 (,8He)
IUCF
K600
44.4 MeV/A
140 keV
PRL 79 (1997) 3845
1999 (t,3He)
NSCL
S800
115 MeV/A,
200 keV
PRC74 (2006) 024309
NIM A432 (1999) 299
24
Mg(p,p'): RCNP and iTL