1. 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 Diagnostics
Moscow, 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

2. Introduction: Principles of the Gamma-Ray Diagnostics
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) 2
10th Meeting of the ITPA Topical Group on Diagnostics, Moscow, 10 – 14 April 2006

3. Some examples of diagnostic reactions
Gamma-Ray Diagnostics provide information on the fast alpha-particles and other fast ions (H, D, T, 3He):
Fast ions sources in plasmas:
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
Some examples of diagnostic reactions
Reaction
Energy of Reaction
Q (МэВ)
Energies of gamma rays
D(t,γ)5He
16.63
16.7
9Be(d,pγ) 10Be
4.59
3.37, 5.96
9Be(d,nγ) 10B
4.36
2.88,
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 3
10th Meeting of the ITPA Topical Group on Diagnostics, Moscow, 10 – 14 April 2006

4. -particle diagnosis is based on -ray emissions from the nuclear reactions 9Be(,n)12C and T(d,)5He
-particles source (16.7-MeV ’s):
4He+n
D+T
5He+ (16.7 MeV)
E, MeV n2 n1 n0
7,65
4,44
12 C Jπ 0+ 2+
Cross section, mb 1 2 3 4 5 6 7
100
200
300
400
500
600
4.44 MeV
7.65 MeV
-particle energy, MeV
/n ≈ (1.2 ±0.3)×10-4
/J.E.Kammeraad et al 1993 Phys.Rev.C 47,29/
Confined -particles (4.44-MeV ’s):
9Be +  = 13C* n C*  12C
Q(Be+-n) = 5.7 MeV
Fusion power 500 MW
MCNP calculations for Radial Neutron Camera with 1m 6LiH plug
E γ =16,7 MeV:
I γ16.7= 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
Excitation functions of the 4.44 and 7.65 MeV levels of 12C in reaction 9Be(,n)12C. 4
10th Meeting of the ITPA Topical Group on Diagnostics, Moscow, 10 – 14 April 2006

5. Distinguish signals related to -particles and D-ions in JET
9Be(4He, nγ )12C
12C(D, pγ )13C
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.
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 5
10th Meeting of the ITPA Topical Group on Diagnostics, Moscow, 10 – 14 April 2006

6. 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

7. 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

8. Neutron Attenuator
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):
(DT- neutrons).
(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 8
10th Meeting of the ITPA Topical Group on Diagnostics, Moscow, 10 – 14 April 2006

9. GAMMACELL spectrometer:
The GAMMACELL PARAMETERS:
9 BaF2 optically independent detectors
energy range: MeV;
energy resolution: 13% @ MeV;
full energy peak efficiency up to 4.44 MeV;
minimum sensitivity to low energy scattered gammas and neutrons.
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
1.2
Energy MeV
7 %
>13%
>11% 3%
10%
7-9%
Decay Time, ns
230
300
0.8/620 16 40 17 9
10th Meeting of the ITPA Topical Group on Diagnostics, Moscow, 10 – 14 April 2006

10. Development of advanced Data Acquisition System
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
0.5
1.0
1.5
2.0
2.5
3.0 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. 10
10th Meeting of the ITPA Topical Group on Diagnostics, Moscow, 10 – 14 April 2006

11. Tests of new DAQ on cyclotron beam
Experimental input data:
4He+ 3.5 MeV beam
On-off time ratio 1/10
Thick Be target
NaI(Tl) detector Ø150×100mm, 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 11
10th Meeting of the ITPA Topical Group on Diagnostics, Moscow, 10 – 14 April 2006

12. Advanced DAQ installed on JET
3.09 MeV
3.68 &
3.85 MeV
Pulse No.65147
NBI blips
4.44 MeV
Spectrum recorded by NaI(Tl) detector with new DAQ during JET plasma discharge #64338.
Time evolution of gamma radiation recorded by new DAQ with integration time 20 ms. 12
10th Meeting of the ITPA Topical Group on Diagnostics, Moscow, 10 – 14 April 2006

13. Conclusions -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
High efficiency and fast -ray spectrometry DAQ has been developed and installed on JET
The DAQ has been tested and fully operational on JET : 0.5 MHz were recorded during NBI injection
6LiH neutron attenuator has been developed and tested. Will be delivered to JET this year.
Scheme of the diagnostics integration in ITER is proposed 13
10th Meeting of the ITPA Topical Group on Diagnostics, Moscow, 10 – 14 April 2006