National Institutes of Natural Sciences, National Institute for Fusion Science
Department of Helical Plasma Research, Fundamental Physics Simulation Research Division

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"Numerical Investigation on Applicability of jC-Measurement Method to Multiple High-Temperature Superconducting Tape"
T. Yamaguchi, H. Ohtani, S. Satake, N. Yanagi, and Y. Onodera,
Plasma and Fusion Research Vol. 17, 2405035 (2022)

We develop a numerical code based on the edge-based finite element method to investigate the applicability of the permanent magnet method to vertically-stacked multiple high-temperature superconducting (HTS) tapes. The permanent magnet method can measure the critical current density in the HTS tape contactlessly and nondestructively. By using our numerical code, it is clear that the permanent magnet method can be applied to measurement of the critical current density in the multiple HTS tapes although there is an upper limit of the number of HTS tapes in which the critical current density can be measured. In addition, by using stronger magnet, the permanent magnet method can measure the critical current density when more number of HTS tapes are stacked.
"Virtual-reality visualization of loss points of 1 MeV tritons in the large helical device, LHD"
H. Ohtani, S. Masuzaki, K. Ogawa, and S. Ishiguro,
Journal of Visualization Vol. 25, 281 (2022)

Intersection points of 1 MeV tritons and the plasma facing wall are visualized in the vacuum vessel of Large Helical Device (LHD) with the divertor plates by the virtual-reality (VR) system. It is possible to directly observe the strike points distributed on the wall and on the plates. This visualization helps us to determine where the material probes should be placed on the plasma facing wall in the real LHD for experimental analysis of the accumulated tritium on the plasma facing wall.
"Linear analysis of cross-field dynamics
with feedback instability
on detached divertor plasmas"
H. Hasegawa, H. Tanaka, and S. Ishiguro,
Nuclear Fusion Vol. 61, 126005 (2021)

The theoretical model of the feedback instability is proposed to explain the mechanism of the correlation between the detachment and the cross-field plasma transport. It is shown that the feedback instability on the detached divertor plasma can be induced in a certain condition in which the volume recombination frequency is larger than the ion cyclotron frequency in the recombination region (see the left figure). The feedback instability can provide the cross-field plasma transport in the boundary layer of magnetic fusion torus devices (see the right figure). Furthermore, the properties of the radial transport observed in the NAGDIS-II linear device experiment are compared with the estimation by the feedback instability model. The dependence of the feedback instability mode on the total collision frequency and the recombination coefficient and the density gradient has been also investigated.
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