Gamma Ray Spectrometry System Design for ITER Plasma Diagnostics
A.E.Shevelev, I.N. Chugunov, D. Gin Ioffe Physico-Thechnical InstituteSaint Petersburg, Russia
10th Meeting of the ITPA Topical Group on DiagnosticsMoscow, 10 – 14 April 2006
Outline:• Introduction: Principles of the Gamma-Ray Diagnostics• Gamma-Ray System in ITER• Technical Requirements for the Gamma-Ray diagnostics• Conclusion
10th Meeting of the ITPA Topical Group on Diagnostics, Moscow, 10 – 14 April 2006
Goals of the diagnosis…Goals of the diagnosis…in D-T plasmas:
-particle birth profile / 16,7 MeV gammas
confined 2-MeV -particle profile / 9Be(,n)12C
distinguish the 1-MeV deuterons and alphas / 9Be + D reactions
escaping -particles / 10B-targets mounted on first wall in detector LOS
in Zero and Low Activation Phases (He, H, D):
ICRF heating optimization
fast-ion distribution function
topology of the fast-ion orbits
the response to plasma instabilities ( sawteeth, TAE modes)
Introduction: Principles of the Gamma-Ray Diagnostics
2
10th Meeting of the ITPA Topical Group on Diagnostics, Moscow, 10 – 14 April 2006
Fast ions sources in plasmas:
Some examples of diagnostic reactions
Reaction Energy of Reaction Q (МэВ)
Energies of gamma rays
D(t,γ)5He 16.63 16.79Be(d,pγ) 10Be 4.59 3.37, 5.969Be(d,nγ) 10B 4.36 2.88, 2.15 12C(d,pγ) 13C 2.72 3.1
9Be(4He,nγ)12C 5.70 4.44, 3.21(from level 7.65)10B(4He,pγ)13C 4.06 3.1, 3.68, 3.85
Gamma-Ray Diagnostics provide information on the fast alpha-particles and other fast ions (H, D, T, 3He):
D+D = t(1,0 MeV) + p(3,0 MeV) D+ He3= He4(3,7 MeV) + p(14,7 MeV)
D+D = He3(0,8 MeV) + n(2,5 MeV) T+T = He4(3,7 MeV) + n +n +11,3 MeV
D+T = He4(3,5 MeV) + n(14,0 MeV) ICRF & NBI heating
3
10th Meeting of the ITPA Topical Group on Diagnostics, Moscow, 10 – 14 April 2006
-particle diagnosis is based on -ray emissions from the nuclear reactions 9Be(,n)12C and T(d,)5He
Excitation functions of the 4.44 and 7.65 MeV levels of 12C in reaction 9Be(,n)12C.
9Be + = 13C* n 12C* 12C
Confined -particles (4.44-MeV ’s):
Q(Be+-n) = 5.7 MeV
/n ≈ (1.2 ±0.3)×10-4
/J.E.Kammeraad et al 1993 Phys.Rev.C 47,29/
4He+n D+T 5He+ (16.7 MeV)
-particles source (16.7-MeV ’s):
E, MeVn2
n1
n0
7,65
4,44
0
12 C
Jπ
0+
2+
0+
Cro
ss s
ect
ion
, mb
1 2 3 4 5 6 70
100
200
300
400
500
600
4.44 MeV 7.65 MeV
-particle energy, MeV
Fusion power 500 MWMCNP calculations for Radial Neutron Camera with 1m 6LiH plugE γ =16,7 MeV: I γ16.7= 2.104 cm-2s-1 B/g: < 10 cm-2s-1
E γ =4,44 MeV (nBe = 1% ne):
I γ4,44= 2*103 cm-2s-1 B/g: ~ 2*103 cm-2s-1
Time resolution: < 100 ms 4
10th Meeting of the ITPA Topical Group on Diagnostics, Moscow, 10 – 14 April 2006
Tomographic reconstructions of 4.44MeV γ -ray emission from the reaction 9Be(4He, nγ)12C and 3.09MeV γ -ray emission from the reaction 12C(D, pγ)13C deduced from simultaneously measured profiles.
V.G. Kiptily et al. Nucl. Fusion 45 (2005) L21–L25
Gamma-ray spectra measured by the NaI(Tl) detector: red line - spectrum recorded in discharge with 70 and 110 keV 4He-beam injectors; blue line - spectrum recorded in a discharge with two 70 keV 4He-beam injectors.
1 2 3 4 5 6 7 80
100
200
300
400
500
600
700 110 & 70 keV 4He-beam
70 keV 4He-beam
9Be( 4He,n) 12CE=4.44 MeV
12C(D,p)13
CE=3.1 MeV
Co
un
ts
Gamma-ray, energy, MeV
9Be(4He, nγ )12C 12C(D, pγ )13C
Distinguish signals related to -particles and D-ions in JET
5
10th Meeting of the ITPA Topical Group on Diagnostics, Moscow, 10 – 14 April 2006
Gamma-Ray System in ITER
Scheme of ITER-FEAT Radial Neutron Camera’s arrangement.
Version of Vertical Camera’s arrangement
Two perspectives of view are required for tomography reconstruction.
6
10th Meeting of the ITPA Topical Group on Diagnostics, Moscow, 10 – 14 April 2006
Technical Requirements for the Gamma-Ray Diagnostics
Minimization of background (gamma and neutron) detector loading /
collimator system with neutron attenuators
High efficiency of gamma-ray registration & High count-rate PHA /
fast heavy scintillators and advanced DAQ
Gain stability (energy resolution) at fast rate-variations / analogous
and digital PMT gain stabilization
7
10th Meeting of the ITPA Topical Group on Diagnostics, Moscow, 10 – 14 April 2006
6LiH neutron plugs provide a high attenuation of the neutron flux without significant losses of gamma-ray counts:
Calculated attenuation factors are approximately (for attenuator with 1 m in length):
• 10 4 (DT- neutrons).
• 10 8 (DD-neutrons)
Gamma-ray measurements at the JT-60U tokamak, during experiments with deuterium NB heated plasmas, showed that using the 30-cm plug reduced the neutron-induced gamma-ray background by a factor of 10.
According to MCNP calculations 35% of 16.7-MeV gamma-rays pass through the filter with 1 m in length without interaction.
6LiH attenuator satisfies the safety requirements and will be installed on JET
Neutron Attenuator
8
10th Meeting of the ITPA Topical Group on Diagnostics, Moscow, 10 – 14 April 2006
Novel fast and heavy scintillates are available (LaBr3, LYSO, LuAP, etc):Property NaI(Tl) BGO BaF2 LaBr3:Ce LYSO:Ce LuAP
Density, g/cm-3 3.67 7.13 4.89 5.3 7.1 8.3
Attenuation length, cm 2.5 1.04 2.1 2.1 1.2 1.04
Energy Resolution @0.661 MeV 7 % >13% >11% 3% 10% 7-9%
Decay Time, ns 230 300 0.8/620 16 40 17
The GAMMACELL PARAMETERS:• 9 BaF2 optically independent detectors• energy range: 1 - 30 MeV;• energy resolution: 13% @ 1.33 MeV;• full energy peak efficiency up to 58% @ 4.44 MeV;• minimum sensitivity to low energy scattered gammas and neutrons.
GAMMACELL spectrometer:
9
10th Meeting of the ITPA Topical Group on Diagnostics, Moscow, 10 – 14 April 2006
0 0.5 1.0 1.5 2.0 2.5 3.0
0
5
10
15
20
25
30
CANBERRA ADC
Fast ADC
Sγ (511 keV), a.u.Count rate, *105 Hz
Gammas recorded by NaI(Tl) vs. the input count- rate. Red dots - conventional ADC; black dots - fast ADC.
Developed advanced DAQ uses fast ADCs, which periodically digitise signals from detectors with high sampling rate. in processing the data stored during the discharge, a special code is used to find pulses, separate superimposed pulses, using known parameters of pulse shape, calculate their amplitudes, and plot the amplitude spectra. The time intervals in which the amplitude spectrum is plotted can be specified and changed in the course of processing. Released option: PCI board specifications:• Channel sampling rate: up to 64 MHz • 4 independent input channels• Resolution: 14 bit• External/program start/stop• Memory on the board: 2 GB
Development of advanced Data Acquisition System
10
10th Meeting of the ITPA Topical Group on Diagnostics, Moscow, 10 – 14 April 2006
1 2 3 4 5 60
2 0 0 0
4 0 0 0
6 0 0 0
8 0 0 0
6 1 0 5 c p sC
ount
s pe
r C
hann
el
E n e r g y , M e V
9 B e ( , n1) 1 2 C E = 3 . 5 M e V
1 2 3 4 5 60
2 0 0
4 0 0
6 0 0
8 0 0
1 0 0 0
4 . 4 3 8 - 0 . 5 1 1 M e V
Cou
nts
per
Cha
nnel 4 . 4 3 8 M e V
6 1 0 4 c p s
N a I ( T l ) 1 5 0 1 0 0 m m1 0 % @ 0 . 6 6 1 M e V
Experimental input data:• 4He+ 3.5 MeV beam• On-off time ratio 1/10• Thick Be target • NaI(Tl) detector Ø150×100mm, 10% @ 0.661 MeV• Detector count rate range (Eγ>0.5 MeV) 10 kHz – 2 MHz • ADC sampling rate 25 MHz
Results:• Energy resolution is stable in count rate range up to 600 kHz (for NaI(Tl) detector)• Counting efficiency of new DAQ at 600 kHz rate is 65%• Digital data processing allows PMT gain stabilization
Tests of new DAQ on cyclotron beam
11
10th Meeting of the ITPA Topical Group on Diagnostics, Moscow, 10 – 14 April 2006
2000 3000 4000 5000 6000 7000 8000 9000 100000
100
200
300
400
500
Cou
nts
per
Cha
nnel
Energy, keV
#64338NaI(Tl)
Advanced DAQ installed on JET
Spectrum recorded by NaI(Tl) detector with new DAQ during JET plasma discharge #64338.
4.44 MeV
3.68 &3.85 MeV
3.09 MeV
48 50 52 54 56 58 600
20
40
60
80
100
120
140
160
180
200
220
Cou
nts
Time, s
Time evolution of gamma radiation recorded by new DAQ with integration time 20 ms.
NBI blips
Pulse No.65147
12
10th Meeting of the ITPA Topical Group on Diagnostics, Moscow, 10 – 14 April 2006
Conclusions
1. -ray spectrometry can provide in ITER:
• Time-resolved spatial measurements of confined -particles in the plasma core
• Ability to distinguish the -particles and other ions
2.High efficiency and fast -ray spectrometry DAQ has been developed and installed on JET
3.The DAQ has been tested and fully operational on JET : spectra @ 0.5 MHz were recorded during NBI injection
4. 6LiH neutron attenuator has been developed and tested. Will be delivered to JET this year.
5.Scheme of the diagnostics integration in ITER is proposed
13