Neutron and gamma ray measurements for fusion experiments and spallation sources Carlo Cazzaniga prof.ssa Claudia Riccardi 1 External supervisor: dr. Marco Tardocchi Supervisor: 1) Istituto di Fisica del Plasma Piero Caldirola 1
Overview Motivation Gamma ray spectroscopy for fusion plasmas with the LaBr3 detector Development of neutron detectors Gas detector for thermal neutrons Proton recoil spectrometers for fast neutrons 2
Why is fast ion physics important in fusion research? The Tokamak is the most promising configuration for magnetic confinement fusion Need for diagnostics neutron and gamma spectrometers Good confinement of alphas is essentially required in realizing a nuclear fusion reactor 3
Neutron detectors for spallation sources Why do we need new thermal neutron detectors? The shortage of 3He has triggered the search for effective alternative neutron detection technologies Why wide do we need a wide energy range neutron spectormeter? Spectrum up to 800 MeV ISIS spallation source Study of single event effects due to atmospheric neutrons 4
Gamma ray spectroscopy for fusion plasmas with the LaBr3 detector 5
Why measuring γ-rays? Gamma-rays are emitted from reactions of fast ions (E>0.5 MeV) with impurities α + 9Be 1n + 12C* 4 12C + γ (4.44 MeV) Studies of fast ions physics α particles confinement Informations from gamma-ray spectroscopy: Good energy resolution peak shape analysis (Doppler broadening) High rate to follow transients associated with MHD instabilities 6
The LaBr3 scintillator Good energy resolution: High light yield (63000 photons per MeV) High efficiency (25% for 4.44 MeV gammas) Big volume (3 x6 cylinder) High Z and high density (5.08 g/cm3) High rate capability (up to 2MHz): Fast scintillation time (16 nsec) PMT with active voltage divider ADC acquisition (400 MHz, 14 bit) 7
Validation with radioactive sources Good energy resolution thanks to high light yield. Spectral shape as expected (full energy peaks, compton edges, backscatt. peak) Good agreement with MCNP simulation. Small difference is ascribed to minor differences between the MCNP model and the actual experimental setup Peak Eγ (kev) R (%) 662 3.3 Co 1173 2.5 Co 1333 2.4 Cs 137 60 60 8
Detector setup at JET LaBr3 LaBr3 ~4m The detector is now installed at JET above the roof lab. It shares the vertical line of sight with other gamma-ray detectors (HPGe, NaI) 9
Fast ion studies using γ ray emission spectroscopy at JET Low density plasmas with high ICRH (Ion Cyclotron Resonance Heating) RF power Several γ-ray peaks are observed from different reactions among fast ions and impurities, such as 9Be(α,nγ)12C, 12C(d,pγ)13C and 9Be(d,pγ )10Be, and have energies from E = 3 to 4.5 MeV. γ 10
Detector response to neutron background elastic inelastic (n,2n) Radiative capture others 2.5 MeV La139: 3 b Br81: 2 b Br79: 2 b La139: 2 b Br81: 1.8 b Br79: 1.8 b 0 10-2 b 0 14 MeV La139: 4 b Br81: 3 b Br79: 2 b La139: 0.6 b Br81: 0.3 b Br79: 0.3 b La139: 1.5 b Br81: 1 b Br79: 1 b 10-3 b < 0.2 b Cross sections relevant for fusion neutron background Inelastic scattering gammas (n,2n) gammas + more neutrons inelastic scattering gammas Delayed counts: 79Br (n,2n) 78Br 81Br (n,2n) 80Br 78Se + β+ (τ = 9 min) (e.p. 2.6 MeV) (90%) 80Kr + β- (τ = 25 min)(e.p. 2 MeV) (10%) 80Se + β+ (τ = 25 min)(e.p. 0.4 MeV) 11
Outline of measurements and simulations Fusion plasmas AUG (DD reaction, 2.5 MeV neutrons) JET (DD reaction, 2.5 MeV neutrons) Frascati Neutron Generator (FNG) DD reaction, 2.5 MeV neutrons DT reaction, 14 MeV neutrons Simulations Simple model: mono-energetic neutrons on crystal only Simulation of produced gamma rays Simulation of detector response 12
Neutron induced background spectrum Simulations of 2.5 MeV neutrons agree with data Different measurements confirm it's neutrons 13
High rate neutron measurements at JET Temporal evolution of the counting rate of the LaBr3 spectrometer and JET total neutron yield measured with the fission chambers for discharge #82539. DD plasmas with high NBI (Neutral Beam Injection) have a high neutron yield, mostly from beam-plasma reactions 14
Measured (linear fit) slope intercept Predicted (MCNP + transport) 0.88 10-10 (0.9 ± 0.3) 10-10 2 103 1.5 103 15
How to handle neutron background on ITER? Neutron flux at this position: up to ~ 108 109 neutron cm-2 s-1 on the detector: 5 109 5 1010 neutrons / sec TO DO NEXT Detailed MCNP simulations Characterization of neutron shielding (6LiH) Line of sight optimization 16
Gas Electron Multiplier for thermal neutron detection 17
bgem for thermal neutrons Neutron conversion Charge particle detector Ions 40 % 60 % Electrons GEM (Gas Electron Multiplier) The 10 B(n,α)7 Li reaction thermal neutrons Single Boron Layer: Low efficiency (1%) Three-dimensional structures: What efficiency can we achieve? 18
Testing the prototype IN THE LAB Assembly of the bgem detector using the cathode with single converter layer. Calibration with X-ray sources Gain as function of measurement parameters Response to background gamma rays AT THE NEUTRON SOURCE First measurement of thermal neutron with single converter layer 19
Characterization of a GEM detector Peak position changes with the gain Photo-peak of 55Fe (6 kev) 20
Experimental test at ISIS The bgem detector successfully measured the thermal neutron beam profile a TOF measurement was performed Beam Profile Measurement and detector counting rate using Cd filters (imaging) Thermal neutron efficiency as a function of the detector gain 21
Telescope Proton Recoil spectrometers 22
TPR detection principle Energy range Efficiency Energy resolution choose Target thickness and area Angle and distance Proton spectrometer (type, material, dimensions) Acquisition system 23
TPR for fusion Two prototype of proton spectrometers (YAP and LaBr3 scintillators) tested in the lab with X and gamma rays Gamma and neutron background evaluated through MCNP simulations and measurements at FNG Peak Energy Cs137 Co60 Co60 LaBr3 YAP Resolution Resolution 662 kev 4.2% 1172 kev 3.5% 1333 kev 3.7% 5.5% 3.8% 3.8% 24
TPR for spallation sources neutrons Phototube YAP 1''x1'' Pulse acquired with digital system Test at ISIS spallation source n Mounting in Milano 25
Results of first test at ISIS Gamma flashes Fast neutron events Some recoil protons observed, but bkg is too high T must stand for Telescope need for delta E detector 26
Conclusion What is the right measurement technique for your application? Gas detector with boron layer The LaBr3 gamma ray spectrometer Diamond detectors Proton recoil spectrometers 27
Courses Schools Sokendai Asian Winter School 2011: " New direction of plasma physics and fusion science for future energy " 11th Kudowa Summer School: "Towards Fusion Energy" MCNPX Intermediate Workshop Classes Radioattività Introduzione alla fisica dello stato solido 28
Publications Papers on peer-reviewed journals C. Cazzaniga et al. Response of the LaBr3 gamma-ray spectrometer to fusion neutrons, to be submitted M. Nocente, M. Garcia-Munoz, G. Gorini, M. Tardocchi, A. Weller, S. Akaslompolo, R. Bilato, V. Bobkov, C. Cazzaniga, B. Geiger, G. Grosso, A. Herrmann, V.G. Kiptily, M. Maraschek, R. McDermott, J.M. Noterdaeme, Y. Podoba, G.Tardini and the ASDEX Upgrade Team, "Gamma-ray spectroscopy measurements of fast ions on ASDEX Upgrade", Nucl. Fusion 52 (2012) 094021 Conference proceedings C. Cazzaniga, M. Nocente, M. Tardocchi, L. Giacomelli, G. Croci, C. Riccardi and G. Gorini, The LaBr3 Gamma Ray Spectrometer for ITER diagnostics, proceedings of the 11th Kudowa Summer School, Towards Fusion Energy, June 11-15, 2012 Nocente, M. Angelone, C. Cazzaniga, I. Chugunov, R.C. Pereira, G. Croci, D. Gin, G. Grosso, A. Neto, A. Olariu, S. Olariu, M. Pillon, A. Shevelev, J. Sousa, M. Tardocchi and G. Gorini, Gamma-ray measurements and neutron sensitivity in a fusion environment, Proceedings of the 1st International Conference on Fusion for Neutrons and Subcritical Nuclear Fission, Varenna, 2011 29
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