Gamma Ray Spectrometry System Design for ITER Plasma Diagnostics

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


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

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-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


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


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


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

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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

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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:

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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


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

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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

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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

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Gamma Ray Spectrometry System Design for ITER Plasma Diagnostics

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