Neutron spectrometry in fusion energy research Göran Ericsson, Erik Andersson Sundén M.Cecconello, S.Conroy, M.Gatu Johnson, L.Giacomelli, C.Hellesen, A.Hjalmarsson, J.Källne, E.Ronchi, H.Sjöstrand, M.Weiszflog Uppsala University G.Gorini, M.Tardocchi, J.Sousa, A.Murari, S.Popovichev Milano-Bicocca, IST, JET Outline: Neutron emission in fusion experiments Role of diagnostics, measurement conditions Spectrometer design and techniques The ToF technique; TOFOR Thin-foil proton recoil technique; MPRu Outlook and Conclusions Frontiers … Rome, 2009 1 See also poster by E.Andersson Sundén

Neutron emission Fusion experiments with D and T fuel: “Impurities” Thermal RF RF Simulation JET; D Fusion experiments with D and T fuel: d + d  3He + n (2.45 MeV) d + t  4He + n (14.0 MeV) “Impurities” d + 3He, 4He, 9Be, 12C, ...  n + X Plasma parameters: Pfus, Ti, f(vion),… Fuel ion velocity populations: Thermal  f(En) Gaussian RF heating  f(En) anisotropic, double humped Beam heating, alpha heating, … Spectral components (ITER): Thermal bulk Sn  1, Beam heating Sn  0.1, RF heating Sn  0.01, a heating Sn  0.001, Neutron emission variations: Intensity; 0 - 1020 n/s (ITER) Temporal (ms), spatial (cm) Scatter Background T = total spectrum, B = thermal bulk NBI = neutral beam AKN = alpha knock-on Simulation ITER; DT n rate JET; D Rn [1015 s-1] Frontiers … Rome, 2009 2

Role and situation for diagnostics Provide information on relevant plasma/fuel ion parameters Feed-back for active control; ms time frame Extended n source (100 m3), “continuous” n emission (min) Collimated LOS, direct + scattered spectral contributions Reliable, robust techniques Harsh experimental conditions around the “reactor” Neutron and gamma background High-frequency EM interference High levels of temperature, B-field Competition over “real estate”; LOS, position, weight, space, … Challenges for neutron spectroscopy Results on ms  spectroscopy on MHz signal rates (Ccap) High e OR close to reactor core Access to weak emission components  high S/B ratio > 104 Peaked, well-known response function (0 – 20 MeV) Real-time information in ms  data acq., processing, transfer Frontiers … Rome, 2009 3

Neutron spectroscopy techniques Most “standard” n spectr Neutron spectroscopy techniques Most “standard” n spectr. techniques tested in fusion (JET) NE213, Stilbene, nat. + CVD diamond Reginatto, Zimbal, RSI 79 (2008)- PTB work Krasilnikov, Rev Sci Instr 69 (1997) Lattanzi, Angelone, Pillon , Fus Eng Des (2009) TOFOR - UU Gatu Johnson, NIM A591 (2008) Frontiers … Rome, 2009 4 TANDEM (TPR) - Harwell Hawkes, RSI 70 (1999) 1134 MPRu - UU Andersson Sundén, NIM A610 (2009)

Time-of-flight Optimized for Rate Optimized for 2.45 MeV n in D plasmas Continuous source of n: Double scattering in S1 + S2 16m from plasma 2m concrete floor Fast plastic scintillators: 5x S1 disks 32x S2 “umbrella” S2 tilt to compensate for Dtlight e ≈ 1% Background = randoms B  Rn2  S:B  Rn Limitations: “Paralysis” at high Rn Rate in S1 (≈ MHz) Ccap ≈ 500 kHz (S:B ≈ 1) Cmax ≈ 44 kHz (Rn = 1.7∙1016 n/s) Emphasis on rate capability: Digital free-running time stamping Separate, non-correlated p.h. spectra En = 2mnR/ttof2 R n” n’ Frontiers … Rome, 2009 5 n flux

TOFOR – count rate capability Limiting sensitivity: random coincidences No correlated time – p.h. information  Randoms corrected for on statistical level  Uniform level from ttof < 0 Digital time stamping electronics (IST, Portugal) Dead time free: ALL signal events recorded (+ ALL randoms) Event based correlations: reduce randoms, reduce timing walk S1 S2 Frontiers … Rome, 2009 6

Thin-foil Magnetic Proton Recoil Separation of functions: n-to-p conversion in thin (mm) foil Energy (momentum) separation in B-field Counting in position resolved hodoscope (32 phoswich scint.) Focal plane detector (FPD) can be shielded to any required level Detectors need “only” count protons Flexibility: Multiple conversion foils – 2.5/14 MeV Multiple p collimators Background reduction: Concrete + lead radiation shield Phoswich scintillators, tdecay = 2, 180 ns TR digital boards Digital pulse shape discrimination Performance: Ccap >> MHz (Cmax = 0.61 MHz) S:B  20000:1 (14-MeV in DT), TOFOR Frontiers … Rome, 2009 7 5:1 (2.5-MeV in D)

MPR results Strong candidate for ITER Alpha heating in DT; MPR 1997 Observation of weak components Alpha heating signature – knock-on n Phoswich DPSD Scattered n Bgr/statistics Background 14-MeV p LED pulser Phoswich DPSD 2.5 mm 0.3 mm 2.5-MeV p 14-MeV p 14-MeV n Min. ionizing e- Amplitude Qshort Qlong Preliminary phoswich DPSD analysis Protons from T burn-up n (14-MeV) Component at 1% of 2.5 MeV emission LED for PMT gain monitoring system Frontiers … Rome, 2009 8 TR boards: 8 bit, 200 MSPS, 512 MB Baseline restoration, pile-up rejection Standard DPSD: 2D plot of Qlong/Qshort Strong candidate for ITER

The future Conclusions Combined pulse-height/time digitizing boards for ToF Compact spectrometers for neutron camera; NE213, CVDD Neutron spectroscopy system for ITER: 2.5-MeV n spectrometer for D operations; ToF 14-MeV n spectrometer for high power DT; MPR/TPR Real-time applications Innovative, new concepts … Conclusions Harsh experimental conditions; special requirements Challenges for Fusion neutron spectrometry: Count rate capability – provide plasma information Background rejection – study weak emission comp. Dynamic range/sensitivity – varying plasma cond. Frontiers … Rome, 2009 9