01Cp08
大型ヘリカル装置の重水素実験における中性子計測と高エネルギー粒子閉じ込め研究の進展
Progress on integrated neutron diagnostics for LHD deuterium plasma
experiment and energetic particle confinement study
小川 国大、磯部 光孝、長壁 正樹
Kunihiro Ogawa, Mitsutaka Isobe, Masaki Osakabe
自然科学研究機構 核融合科学研究所、総合研究大学院大学
National Institute for Fusion Science, National Institutes of Natural Sciences, The Graduate
University for Advanced Study, SOKENDAI
For realizing a steady state fusion burning
plasma, energetic ion confinement has been widely
studied because the plasma is sustained bydeuterium–tritium fusion born energetic alphaparticles. Close attention has been paid to studying
the confinement of energetic particles, such as beamions and ion cyclotron tail ions. Approaching a
steady state fusion burning plasma, a study ofenergetic particle confinement in stellarators andhelical systems has been led by the Large Helical
Device (LHD) [1]. In hydrogen campaign, the study
was mainly conducted using the charge-exchanged
neutral particle analyzer and escaping energetic ion
diagnostics. We started the deuterium experiment inMarch 2017 to obtain further advances inhelical-type plasma performances and to understandplasma physics. Additionally, the deuterium
experiment aims to demonstrate the capability ofenergetic particle confinement in helical systems
toward a steady state fusion burning plasma. In
neutralbeam(NB)-heated
LHD
plasmaexperiments, neutrons are mainly created bybeam-thermal reactions owing to extreme NB
injection. Therefore, neutron has the information
regarding the beam ions confined in the plasmacore area. The neutron diagnostic of LHD wasplanned in the construction stage of LHD [2].
Installation of neutrons and gamma-ray detectors
were scheduled for measuring the total neutron
emission rate (Sn) and fuel ion temperature as wellas enhancing an energetic particle confinement
study. Neutron diagnostics plan began taking shapesubsequently in 2010 [3]. Candidate detectors formeasuring Sn, neutron emission profile, neutronenergy spectrum, triton burnup, and high-energy
gamma-ray were proposed for the executing
energetic ion confinement studies. The abundanceof neutron diagnostics is compared with that
installed in large tokamaks, i.e., JET, TFTR, andJT-60U [4]. Since expected Sn has similar intensity
compared with deuterium operation executed inlarge tokamaks, the energetic particle confinement
study conducted in LHD is expected to be the samelevel of study conducted in large tokamaks.
A comprehensive set of neutron
diagnostics has been developed for developing theenergetic particle confinement study and radiation
management in LHD. We advanced thedevelopment and establishment of comprehensive
neutron measurement hardware following thestrategy. The five systems, i.e., the ex-vessel NFM,
neutron activation system (NAS), VNC,
scintillating fiber (Sci-Fi) detector, and neutron
fluctuation (NF) detector have been regularlyutilized (Fig. 1). An arrangement of diagnostics
with NB injectors is depicted in Fig. 1. In LHD,
negative ion source-based NB (N-NB) injectors
whose acceleration energy reaches 180 keV
tangentially inject and mainly create co- or
counter-going transit beam ions, while positive ion
source-based NB (P-NB) injectors whoseacceleration energy is up to 60/80 keV
perpendicularly inject and mainly create helicallytrapped beam ions. Moreover, using these intense
NB injectors, a study of energetic particle
confinement is conducted.
Integrated neutron diagnostics developedfor LHD deuterium operation was installed andoperating properly. Based on the neutron diagnostic
plan in LHD, the NFM [5], NAS [6], VNC [7],Sci-Fi detector [8], and NF [9] were established.
NFM having a wide dynamic range, fast time
response, and high noise tolerance was utilized formeasuring Sn. Characterization of Sn of LHD
plasmas, fuel ion temperature evaluation, global
confinement of beam ion, investigation of knock-on
tail formation, and study of beam–beam nonlinear
collision
wasconducted.
TomeasureFig. 1 Arrangement of comprehensive neutron diagnostics in LHD
shot-integrated DD or DT neutron fluence, NAS
having two irradiation ends was utilized.
Additionally, a cross check of NFM, anisotropy ofDD neutron emission, and neutron spectra
measurements were performed. To measure theradial profile of the neutron emission, VNCs
installed at three toroidal angles were utilized.
Measurement of neutron emission profile in N-NBor P-NB-heated plasmas and study of energetic ion
transport owing to energetic ion driven MHD
instability was conducted. Three types of Sci-Fidetector were developed for time-resolved
measurement of DT neutron flux. The timeevolution of the secondary DT neutron emission
rate was compared with numerical simulation basedon classical confinement of energetic ions.
Furthermore, the dependence of DT neutron
emission rate on the magnetic axis position wassurveyed. NF detector having a fast time response
was utilized to measure the rapid change of Sn. In
EIC discharge, the rapid decay of Sn was measured.
Energetic particle confinement study in LHD waslargely advanced by utilizing integrated neutron
diagnostics.
[1] Y. Takeiri IEEE Trans. Plasma Sci. 46 2348
(2018).
[2] M. Sasao et al., Fusion Eng. Des. 34-35 595(1997).
[3] M. Isobe et al., Rev. Sci. Instrum. 81 10D310(2010).
[4] N. Javis Plasma Phys. Contr. Fusion 36 219(1994).
[5] M. Isobe et al., Rev. Sci. Instrum. 85 11E114(2014).
[6] M. Isobe et al., IEEE Trans. Plasma Sci. 462050 (2018).
[7] K. Ogawa et al., Rev. Sci. Instrum. 89 113509(2018).
[8] K. Ogawa et al., Nucl. Fusion 58 034002(2018).
[9] K. Ogawa et al., Plasma Fusion Res. 13
3402068 (2018).