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

Tieshuan Fan （tsfan@pku.edu.cn）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

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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