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

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

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, 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 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 -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 12C*  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= 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 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

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

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

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): 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 8 10th Meeting of the ITPA Topical Group on Diagnostics, Moscow, 10 – 14 April 2006

GAMMACELL spectrometer: 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. 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 Resolution @0.661 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

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

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, 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 11 10th Meeting of the ITPA Topical Group on Diagnostics, Moscow, 10 – 14 April 2006

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

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 : spectra @ 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