Fusion neutron production with deuterium neutral beam injection and enhancement of

energetic-particle physics study in the Large Helical Device

1 National Institute for Fusion Science, National Institutes of Natural SciencesToki 509-5292, Japan

2 SOKENDAI (The Graduate University for Advanced Studies), Toki 509-5292, Japan3 National Institute of Technology, Toyama College, Toyama 939-8630, Japan

4Kyoto University, Kyoto 615-8540, Japan

15th IAEA Technical Meeting on Energetic Particles in Magnetic Confinement Systems, 5-8 September, PPPLSession 8 : Diagnostic Development : O-14

M. Isobe1,2, K. Ogawa1,2, T. Nishitani1, N. Pu2, H. Kawase2, R. Seki1,2, H. Nuga1,E. Takada3, S. Murakami4, Y. Suzuki1,2, M. Yokoyama1,2, M. Osakabe1,2, and LHD experiment group1

1/18

Outline of talk

1) Deuterium operation of LHD

2) Neutron diagnostics prepared for LHD • Neutron flux monitor (NFM)• Neutron activation system (NAS)• Vertical neutron camera (VNC)• Scintillating fiber (Sci-Fi) detector

3) Representative results from 1st deuterium campaign of LHD

4) Summary2/18

First deuterium plasma (#133301)

Group photo after the ceremony (VIPs version)

LHD deuterium operation began in March 7, 2017 after long-term preparation

3/18

Deuterium operation of LHD and expected neutron emission rate

• Deuterium plasma experiment began in LHD to explore higher-performance helical plasmas and to gain a positive prospect toward an LHD-type fusion reactor.

• Neutron yield measurement is essential in the LHD operation, since neutron yield has to be managed in compliance with neutron budgets approved by NRA of JA.

Line-averaged density (x 1019 m-3)

2x1016

1x1016

0

Tota

l neu

tron

em

issi

on ra

te (n

/s)

Expected neutron rate Max. neutron rate is expected to be over 1x1016 (n/s) when full power NB heating is performed.

In LHD, generated neutrons are dominated by neutrons coming from beam-plasma reactions.

Neutron diagnostics play an important role to accelerate understanding of EP physics in LHD plasmas.

4/18

Diagnostics Measurement target Role Status

(1) Neutron flux monitor • Total neutron rate, yield

• Neutron yield management• Fusion output• Global fast-ion confinement

Working

(2) Neutron activation system

• Total neutron yield• Secondary DT neutron yield

• Neutron yield management• Triton burnup

Working

(3) Vertical neutron camera • Neutron emission profile

• Beam ion profile• Beam-ion transport by EPM/AE

Working

(4) Fast-neutron scintillation detector

• Neutron fluctuation • Beam-ion transport by EPM/AE Working

(5) Sci-Fi detector • Secondary DT neutron rate • Triton burnup Working

(6) g-ray scintillation detector • Prompt g-ray flux

• Confinement of MeV ion• D-3He reaction rate in the future

Working

A comprehensive set of neutron and gamma-ray diagnostics prepared for the LHD deuterium campaign

Development of DD neutron spectrometer will be initiated in FY2017 to measure fast-ion velocity distribution in a plasma core in the collaboration with Peking Univ.

5/18

• 235U FC can work in a high-neutron yield shot, playing an important role in neutron yield management and energetic-particle physics study.

• 10B and 3He counters are used for a low-neutron yield shot, e.g. ECRH plasma w/o NB.

LHD is equipped with three ex-vessel NFMs characterized by fast-response and wide dynamic range capabilities

・Thermal neutron sensitivity : 0.1 (cps/nv)

235U fission chamber (FC)

10B counter

3He counter ・Thermal neutron sensitivity : 6.5 (cps/nv)

・Thermal neutron sensitivity : 39 (cps/nv)

FC up to 5x109 (cps)

• In situ NFM calibration was performed to evaluate total neutron emission rate.• The calibration was carried out along the method standardized in the WS on the

neutron calibration held at PPPL in 1989. (J.D. Strachan et al., Rev. Sci. Instrum. 61(1990)3501.)• Relation between neutron rate Sn and pulse counting rate Crate is expressed as

Coefficient a is obtained by using a neutron source whose neutron rate is known.

Neutron detectors(235U, 10B, 3He)

Track placed at Rax of 3.74 mActivation foil

252Cf source intensity : 800 MBq (~108 (n/s))

In situ NFM calibration on LHD in Nov., 2016 (1)

Sn (n/s) = a× Crate (cps)

M. Isobe et al., Rev. Sci. Instrum. 81 (2010)10D310.

7/18

In situ NFM calibration on LHD in Nov., 2016 (2)

N

K

O

M

R

J

T

U

I

Y

X

W

V

L

S

D

Q

P

B

H

F

B

C

G

E

A

線源容器クレーンで搬入のため、近辺の機器とある程度間隔が必要

作業位置3mの棒により、線源を容器から列車に移すため4mほど必要

人が入るため通路が必要

作業領域を右側にとることも可

DDファーストプラズマ前の較正実験まで使用。現在の予定では、平成26年12月まで。

それ以降は、大きな装置の改造がない限り使用しないが、再び行う場合に、作業領域が確保できるようにお願いします。

TrainStation

•The train loaded with 252Cf ran continuously inside the VV.

•Calibrations with continuous run were performed seven times with different discrimination levels of FC.

•Point-by-point measurements were also carried out.

8/18

235U fission chambers

10B and 3He counters

Neutron pulse counts during in situ calibrationDependence of detection efficiency on source toroidal angle

Sn (n/s) = a× Crate (cps)

Coefficient a for primary FC(TOP) : 1.46x1089/18

Neutron emission rate measured with NFM in LHD (1)

Systematic survey of neutron emission rate for beam-heated plasmas

• Sn in Rax of 3.6 m is the highest.• It tends to decrease as Rax is shifted

outwardly as expected.

Highest neutron rate shot in 1st D campaign

Time (s)

3.3x1015 (n/s)

10/18

Perpendicular beam blip injection into an ECRH plasma

Neutron emission rate measured with NFM in LHD (2)

• Peak value of Sn increases as ne increases as expected according to increase of beam deposition.

• Neutron decay time tends to be shorter (longer) as ne increases (decreases). This tendency is consistent with that predicted by classical slowing-down theory 11/18

Central fuel ion temperature evaluated from neutron emission rate in an ECRH deuterium plasma of LHD

Waveforms of ECRH discharge Time evolutions of Td(0) and Timp

• Total neutron emission rate, profile deduced from TS, and H/D ratio are used.• Zeff is assumed to be 2. • Td(0) evaluated by neutron emission rate is consistent with Timp(Ar) measured with X-

ray crystal spectroscopy diagnostic.

T d(0

)

K. Ogawa, M. Isobe et al., accepted for publication in Plasma and Fusion Research.

Time (s)

12/18

10B counter

1011 1012 1013 1014 10151011

1012

1013

1014

1015

Neu

tron

yie

ld p

er s

hot e

valu

ated

by

NA

S

Neutron yield per shot evaluated by NFM

• Neutron yield evaluated by NAS agrees well with that measured with NFM.• Also, NAS has been used to measure secondary 14 MeV neutron fluxes by using

28Si(n, p)28Al reaction to study 1 MeV triton’s behavior.

115In(n,n’)115mIn

Pneumatic tubes

StationMeasurement room

HPGe

2.5-L port

Pneumaticcontrol system

The NAS on LHD has two irradiation ends, which perform important roles in cross-checking neutron yield evaluated by the NFM.

13/18

Neutron activation system on LHD

Arrangement of VNC

• Collimator was made of heavy concrete.• Detector can be stably operated up to 106

(cps) with online + offline n-g discrimination capability.

11 channel

Vertical neutron camera on LHD

The peak of line-integrated neutron emission profile shifts outward with an increase of Rax.

•Intermittent decreases of neutron emission rate are observed associated with MHD bursts.•Line-integrated neutron profile suggest that beam ions confined in plasma core region are lost due to MHD modes.

Magnetic fluctuationamplitude

Significant change of neutron emission profiledue to recurrent fast-ion-driven MHD bursts

Shot#141538Rax=3.62 mBt=2.83 T (CCW)

15/18

Study of 1 MeV triton’s behavior by measuring secondary D-T neutron

Time-resolved 14 MeV neutron flux is measured by using scintillating-fiber detectors.Time evolutions of total and

14 MeV neutron rates

1010

1011

1012

1013

1014

1015

1016

3 3.5 4 4.5 5 5.5 6

Shot #:138414

Total neutrons14MeV neutronsN

eutro

n em

issi

on ra

te (n

/s)

NBI

Time (s)

14 MeV n Recoil proton

Scintillation light

• Build-up rate of 14 MeV neutron flux is slower than that of total neutron rate.

• It comes from cross section curve for D-T reaction.

• D+D -> 3He (0.8 MeV) + n (2.5 MeV)• D+D -> T (1 MeV) + p (3 MeV)

Secondary reactionT+D -> 4He (3.5 MeV) + n (14 MeV)

Reactions in a deuterium plasma

16/18

Triton burnup ratio significantly depends on magnetic field configuration

The Sci.-Fi. detector is calibrated by using results measured with calibrated NAS.Triton burnup ratio can be evaluated in every shots.

• Maximum triton burnup ratio is ~0.45% in Rax/Bt of 3.55 m/2.89 T.• Triton burnup ratio decreases as a plasma column is shifted outwardly as

expected from orbit calculations.

Rax=3.6 m

Rax=3.75 m

Rax=3.9 m

Helically trapped orbits

17/18

1) The LHD project stepped into a new stage. The deuterium experiment began in March 7th, 2017 after long-term preparation.

2) A comprehensive set of neutron diagnostics has been installed.

3) Total neutron yield Yn has been measured with a fast response, wide dynamic range NFM, and NAS. • Yn management is essential in the operation of LHD.• Max. counting rate capability of NFM goes up to ~5x109 (cps).• In situ calibration by using 252Cf (800 MBq) was performed in Nov. 2016.• Neutron rate has reached ~3.3 x1015 (n/s) in the inwardly shifted

configuration at Rax of 3.55 m.

4) DD neutron profile has been measured with VNC. Neutron emission profile have changed according to Rax. Significant change of neutron profile was observed due to recurrent fast-ion-driven MHD events.

5) In addition to NFM, VNC, and NAS, scintillating fiber detectors have been used to study confinement property of 1 MeV tritons. Triton burnup ratio decreases as a plasma column is shifted outwardly as expected.

Summary

18/18