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  • 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 Sciences Toki 509-5292, Japan

    2 SOKENDAI (The Graduate University for Advanced Studies), Toki 509-5292, Japan 3 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, PPPL Session 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) Summary 2/18

  • 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

    To ta

    l n eu

    tr on

    e m

    is si

    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。

    Train Station

    •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 calibration Dependence of detection efficiency on source toroidal angle

    Sn (n/s) = a× Crate (cps)

    Coefficient a for primary FC(TOP) : 1.46x108 9/18

  • 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 1015 1011

    1012

    1013

    1014

    1015

    N eu

    tr on

    y ie

    ld p

    er s

    ho t e

    va lu

    at ed

    b y

    N A

    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

    Station Measurement room

    HPGe

    2.5-L port

    Pneumatic control 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 fluctuation amplitude

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

    Shot#141538 Rax=3.62 m Bt=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