The Deuterium-Deuterium Neutron Time-of- Flight Spectrometer TOFED at EAST

Transcription

1 The Deuterium-Deuterium Neutron Time-of- Flight Spectrometer TOFED at EAST Tieshuan Fan Lijian Ge, Tengfei Du, Zhimeng Hu, Yimo Zhang, Jiaqi Sun, Xingyu Peng,Zhongjing Chen, Xing Zhang, Xufei Xie, Xi Yuan, Xiangqing Li, Guohui Zhang, Jinxiang Chen School of Physics, Inst. Heavy Ion Phys., Peking University, Beijing,China in collaboration with Guoqiang Zhong,Liqun Hu, Shiyao Lin,Baonian Wan Institute of Plasma Physics, CAS, Hefei, China G. Gorini*, M. Nocente*, M. Tardocchi*, J. Kallne** *IFP-CNR and Department of Physics, University of Milano-Bicocca, Italy **Department of Engineering Sciences, Uppsala University, Sweden LSC2017, Advances in Liquid Scintillation Spectrometry 1-5th May, 2017, Copenhagen, Denmark

2 Outline Motivations TOFED (Time-of-flight Enhanced Diagnostics ) neutron emission spectrometer Design & Construction (with Plastic Scintillators) New challenges Liquid Scintillators with n/γ discrimination capability Concluding Remarks 2/22

3 Motivations Culham,England 2019? Toki, Japan ITER ~ 2027 DEMO ~ 2050 Hefei, China SWIP, Chengdu, China 2020? CFETR (China Fusion Engineering Test Power Plant ~? Fusion Electricity - EFDA November 2012 Li J.G., et al, Nature Phys. 9 (2013) 817 Duan X.R., et al, Nucl. Fusion. 49(2009) /22

4 Motivations 3 D + D He (0.820 MeV) + n Q = MeV T D The neutron emission is a direct measure of the progress towards D + D T (1.011 MeV) + p Q = MeV the achievement of thermonuclear reactor conditions 4 D + T He (3.561MeV) n Q MeV + = α 3.5 MeV n 14 MeV JET ITER DEMO Neutron Yield: (1/s) 4/22

5 Motivations Ion velocity Distribution Neutron Spectra dn n n F = = δ(e En)f (v )f (v ) v σ v, θ dv dv dω Plasma Physics Information from NES: Ion temperature Ti Fuel ion kinetic information Plasma rotation Knock-on tail effect Auxiliary heating effect Impurity level ( ) A B n A A B B rel rel c A B lab de 1+ δab Ohmic Discharges: D-D plasmas FWHM(keV) = 82.6 T(keV) D-T plasmas FWHM(keV) = T(keV) MPR for DT JET B Wolle Physics Reports 312 (1999) O N Jarvis Plasma Phys Control Fusion 36 (1994) PRL 85(2000) J Kallne TOFOR for DD JET H.Henriksson Plasma Phys. Control. Fusion 47(2005) L Giacomelli Nucl. Fusion 45(2005) B. Esposito Rev. Sci. Instr. 75 (2004) Liquid Scintilaion JT60U 5/22

6 TOFED: design Evaluation of fast ion and neutron emission spectra in EAST with NBI heating and the design of the line-of-sight of TOFED on EAST < 7% Fast ion distributions Presented a Modified HB model to describe the fast ion velocity distributions of EAST plasmas with NBI heating EAST, port H MHB Model Efficiency:> 1.5% SNR: ~ 100 Energy Resolution: Detection Calculated energy distributions of the neutron emission from D plasmas with NB injection -- Basic requirements of Neutron Spectrometer for diagnosing fast-ion distributions, heating effect, high Zhongjing Chen Nucl Fusion 53(2013) X. Zhang Nucl Fusion 54(2014) T. S. Fan, Chin. Science A43(2013)1236 6/22

7 TOFED: design E n = 2m n r/t tof 2 For much lower neutron yield on EAST How to improve energy resolution Time-of-Flight Technique Real energy spectrum meas. Good Energy resolution but Detection efficiency < 0.1% ' 2 En( θ) = Encos θ L( θ) = Dcosθ & to increase detection efficiency? 2 L( θ ) D tof ( θ ) = = = const. m 2En ' 2 En( θ )/ TOFOR (32 S2 channels JET G. Grini & J. Kallne, REV. SCI. INSTRUM., 63,4548(1992) Gatu Johnson M. et al. NIMA, 591, 417(2008) 7/22

8 TOFED: design S2 neutrons S1 TOFED (80 S2 EAST Decreasing the geometric indetermination to improve the energy resolution Increasing the covered solid angle of the scattered neutrons to increase the detection efficiency TOFED=Time Of Flight Enhanced Diagnostics Z.J. Chen, et al., REV. SCI. INSTRUM., 85, 11D830(2014) X. Zhang, et al., NUCL. FUSION, 54, (2014) 8/22

9 TOFED: design Double Dynamic Energy Selection Windows: GEANT4 cal. & experimental results Upper Ring lower Ring kinematics Selection Fixed Windows whole spectrometer 2.45 MeV neutron Flight time vs. the recoil proton Pulse Height in S1 for TOFED A double-ring structure and a pulse shape discrimination technique of new TOFED design allows for a dual kinematic selection in the time-of-flight/recoil proton energy space X. Peng, et al. REV. SCI. INSTRUM., 85, 11E112(2014) 9/22

10 TOFED: design Raw signal Signal after double kinematics Results on simulated TOF spectra for mono-energetic neutron beams Improving the spectrometer capability to resolve fast ion signatures in the neutron spectrum up to a factor ~ 100 for the first time X. Peng, et al. REV. SCI. INSTRUM., 85, 11E112(2014) 10/22

11 TOFED: design Design of S1 and S2 scintillators using GEANT4.9 & ROOT5.2 6 S1 Tilt Angles S1 thickness S1 Covered Area S2 Lenngth vs width S2 thickness S2 Area response matrix single ring double ring Zhang X PLASMA SCIENCE & TECH 14 (2012)675 11/22

12 The birth of TOFED Geometric parameters of scintillation detectors S2 Scintillators EJ200 Parameter S2_upper S2_bottom Radius 750 mm Scintillator EJ200 Scintillator EJ200 Collimator circle Shape trapezoid Shape trapezoid S1 scintillator EJ228 Thickness 17 mm Thickness 17 mm S1 shape cylinder Length 280 mm Length 235 mm S1 thickness 6 mm Width 1 S1 Scintillators 70 mm EJ228 Width 1 95 mm S1 radius 20 mm Width mm Width mm S1 layers 5 Number 40 Number 40 Angle 25 o Angle 35 o 12/22

13 TOFED: construction The LED system with 1*90 splitters is used to determine the time alignment among TOFED 80 detectors with a deviation of ±0.2 ns. y x Experimental The S2 scintillators tilted inwards an angle of 3 degree, which decreases the timing variation from 1.5 ns to 0.6 ns. Simulated photon transport 13/22

14 TOFED: construction Experiments of TOFED with quasi-monoenergetic neutron beams and gamma-ray sources have shown the good background suppression ability 7Li(p,n)7Be reaction 1.4 MeV X Y Peng et al. REV SCI INSTRUM 85(2014)n Peak/Valley > MeV Neutrons Back-scattered gamma Gamma T(p,n)3He reaction

15 TOFED: construction EAST Tokamak 2.5 MeV neutron TOFED Spectrometer Energy resolution ~ 6.6% Detection efficiency(80 S2): ~ 1.5% TOFED 15/22

16 TOFED: new challenges Successful tests Ohmic plasmas backward forward TOFED time-of-flight spectrum of background LHCD plasmas 16/22

17 TOFED: new challenges A big challenge? During EAST engineering adjustment discharges in 2015, the γ/n ratios from TOFED reach very high values 17/22

18 TOFED: new challenges The radiation shielding for TOFED, designed by a detailed MCNP5 model at EAST, was constructed to reduce the random coincidence events by the background radiation which consists mainly of scattering neutrons and gamma-rays m Thickness of polythene:30 cm Thickness of lead:7cm Shield efficiency for neutrons: 10-3 Shield efficiency for gamma-ray: m TOFED in shielding 4 m It was subject to volume and weight (< 18 tons) restrictions at design stage Radiation shielding not enough! T.F. Du, et al. REV. SCI. INSTRUM., 85,11E115 (2014)11E115 18/22

19 TOFED: with n/γ discrimination capability S1: 5 Scintillator cylinders of EJ228 Radius: 750 mm Thickness: 6 mm Radius: 20 mm neutrons γ-rays S2 10 new designed Liquid Scintillators type:ej301 Cylinder size: 2 inch in diameter, 4 inch in height To deduce strong γ-ray background from TOF spectra through 10 Liquid scintillators with good n/γ discrimination 19/22

20 TOFED: with n/γ discrimination capability neutrons 252 Cf γ-rays The measured Time-of-flight spectrum for 252 Cf source in EAST hall Response for different mono-energetic neutrons by PEKING GEANT4 UNIVERSITY simulations. 20/22

21 TOFED: with n/γ discrimination capability Preliminary Results in EAST campaigns neutrons γ-rays Neutron spectra from NUBEAM+GENESIS calculations Measured TOF spectra & Simulated ones for shots ,55280 The measured data are in good agreement with the simulated data, specially for broadening width The different components of neutron spectra are successfully separated for the first time at EAST device Fusion neutrons mainly come from beam-target reactions for this NBI discharge 21/22

22 Concluding remarks TOFED at EAST is the first high performance neutron spectrometer on a long pulse tokamak and it is of relevance as a step in the development of NES diagnostics after JET In 2017, for the remaining 48 S2 detectors [Nucl. Fusion, 54, (2014) ] Delivery of the mechanical and scintillation components Upgrade to 80 S2 channels & engineering adjustments Move TOFED backwards to the outside of EAST experimental hall in order to use the hall wall as the perfect radiation shield