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The Deuterium-Deuterium Neutron Time-of-Flight Spectrometer TOFED at EAST
Tieshuan Fan ([email protected])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 Spectrometry1-5th May, 2017, Copenhagen, Denmark
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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
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Li J.G., et al, Nature Phys. 9 (2013) 817Duan X.R., et al, Nucl. Fusion. 49(2009) 104012
Power Plant ~ ?
ITER ~ 2027
EAST @IPP, Hefei, China
CFETR (China Fusion Engineering Test
Reactor)
Motivations
JET@ Culham,England
HL-2A @ SWIP, Chengdu, China
LHD@NIFS, Toki, Japan
2019 ?
2020 ?
DEMO ~ 2050
Fusion Electricity - EFDA November 2012
3/22
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3
4
D D He (0.820 MeV) 3.269 MeV
D D T (1.011 MeV) p 4.033 MeV
D + T He (3.561MeV) 17.589 MeV
n
n
Q
Q
Q
+ → + =
+ → + =
→ + = α 3.5 MeVn 14 MeV
DT
ITER DEMO
1016
Motivations
JET
Neutron Yield: (1/s)1020 1022
The neutron emission is a direct measure of the progress towards
the achievement of thermonuclear reactor conditions
4/22
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O N Jarvis Plasma Phys Control Fusion 36 (1994) B Wolle Physics Reports 312 (1999)
Ion velocity Distribution Neutron Spectra
Plasma Physics Information from NES:Ion temperature TiFuel ion kinetic informationPlasma rotationKnock-on tail effectAuxiliary heating effect Impurity level……
H.Henriksson Plasma Phys. Control. Fusion 47(2005) L Giacomelli Nucl. Fusion 45(2005)
PRL 85(2000) J Kallne
B. Esposito Rev. Sci. Instr. 75 (2004)
Ohmic Discharges:
FWHM(keV) 82.6 T(keV)=
FWHM(keV) 177.2 T(keV)=
D-D plasmas
D-T plasmas
( )A BA A B B A B lab
AB
n ndN (E En)f (v )f (v ) , dv dvdE 1+n rel rel cF v v dδ σ θ
δ= = − Ω∫∫
MPR for DT neutrons @ JET
TOFOR for DD neutrons @ JET
Liquid Scintilaion detectors @ JT60U
Motivations
5/22
PEKING UNIVERSITYTOFED @ EAST, port H
Calculated energy distributions of the neutronemission from D plasmas with NB injection
Zhongjing Chen Nucl Fusion 53(2013)063023X. Zhang Nucl Fusion 54(2014)104008T. S. Fan, Chin. Science A43(2013)1236
Fast ion distributions
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
Presented a Modified HB model to describe the fast ion velocity distributions of EAST plasmas with NBI heating
MHB ModelEnergy Resolution:
< 7%
Detection
Efficiency:> 1.5%
SNR: ~ 100
-- Basic requirements of Neutron Spectrometer for
diagnosing fast-ion distributions, heating effect, high
energy D behavior MHD activities…
TOFED: design
6/22
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En = 2mnr/ttof2
TOFOR (32 S2 channels ) @ JET
G. Grini & J. Kallne, REV. SCI. INSTRUM., 63,4548(1992)Gatu Johnson M. et al. NIMA, 591, 417(2008)
Time-of-Flight Technique• Real energy spectrum meas.• Good Energy resolution
but • Detection efficiency < 0.1%
' 2
2
'
( ) cos( ) cos
( )( ) .22 ( ) /
n n
nn
E EL D
L Dtof constEE m
θ θθ θ
θθθ
==
= = =
For much lower neutron yield on EAST
How to improve energy resolution
& to increase detection efficiency?
TOFED: design
7/22
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TOFED (80 S2 channels) @ 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 DiagnosticsZ.J. Chen, et al., REV. SCI. INSTRUM., 85, 11D830(2014)X. Zhang, et al., NUCL. FUSION, 54, 104008(2014)
TOFED: design
8/22
S2
S1
neutrons
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Upper Ring
lower Ring
whole spectrometer
Double Dynamic Energy Selection Windows: GEANT4 cal. & experimental results
2.45 MeV neutron Flight time vs. the recoil proton Pulse Height in S1 for TOFED
kinematics Selection
Fixed Windows
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)
TOFED: design
9/22
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Results on simulated TOF spectra for mono-energetic neutron beams
X. Peng, et al. REV. SCI. INSTRUM., 85, 11E112(2014)
Raw signal
Signal after double kinematics
Improving the spectrometer capability to resolve fast ion signatures in the neutron spectrum up to a factor ~ 100 for the first time
TOFED: design
10/22
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Design of S1 and S2 scintillators using GEANT4.9 & ROOT5.2 6
S1 Tilt AnglesS1 Covered Area
S2 Lenngth vs widthS2 Area
response matrix
S1 thickness
S2 thickness
single ring double ring
Zhang X PLASMA SCIENCE & TECH 14 (2012)675
TOFED: design
11/22
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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 70 mm Width 1 95 mm
S1 radius 20 mm Width 2 100 mm Width 2 110 mm
S1 layers 5 Number 40 Number 40
Angle 25o Angle 35o
Geometric parameters of scintillation detectorsThe birth of TOFED
12/22
S2 Scintillators EJ200
S1 Scintillators EJ228
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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.
TOFED: construction
13/22
The S2 scintillators tilted inwards an angle of 3 degree, which decreases the timing variation from 1.5 ns to 0.6 ns.
y
x Experimental
photon transport Simulated
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Experiments of TOFED with quasi-monoenergetic neutron beams and gamma-ray sources have shown the good background suppression ability
2.5 MeV Neutrons
Gamma
Back-scattered gamma
Peak/Valley > 100
X Y Peng et al. REV SCI INSTRUM 85(2014)n
T(p,n)3He reaction
7Li(p,n)7Be reaction
1.4 MeV
TOFED: construction
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Installation @ EAST Tokamak
TOFED: construction
15/22
2.5 MeV neutron TOFED Spectrometer
Energy resolution ~ 6.6%
Detection efficiency(80 S2): ~ 1.5%
TOFED
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Successful tests
forwardbackward
TOFED time-of-flight spectrum of background
LHCD plasmas
Ohmic plasmas
TOFED: new challenges
16/22
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A big challenge ?
During EAST engineering adjustment discharges in 2015, the γ/n
ratios from TOFED reach very high values
TOFED: new challenges
17/22
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Thickness of polythene:30 cmThickness of lead:7cmShield efficiency for neutrons: 10-3
Shield efficiency for gamma-ray: 10-2
4 m
0.9 m
2.83 m
TOFED in shielding
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
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.
TOFED: new challenges
18/22
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neutrons
γ-rays
S1: 5 Scintillator cylinders of EJ228Radius: 750 mmThickness: 6 mmRadius: 20 mm
S2
type:EJ301Cylinder 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/γdiscrimination
10 new designed Liquid Scintillators
TOFED: with n/γ discrimination capability
19/22
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neutrons
γ-rays
The measured Time-of-flight spectrum for 252Cf source in EAST hall
252Cf
TOFED: with n/γ discrimination capability
20/22
Response for different mono-energetic neutrons by GEANT4 simulations.
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TOFED: with n/γ discrimination capability
neutrons
γ-rays
Preliminary Results in EAST campaigns
Neutron spectra from NUBEAM+GENESIS calculations
Measured TOF spectra & Simulated ones for shots 55275-55278,55280
• 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 discharge21/22
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• 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
[Nucl. Fusion, 54, (2014) ]
Concluding remarks
• In 2017, for the remaining 48 S2 detectors
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