Plasma and Fusion Research

Volume 13, 3402024 (2018)

Regular Articles

Fast Ion Confinement Study by Neutron Emission Rate Measurement after Short Pulse NB Injection in the Large Helical Device
Takeo NISHITANI1), Kunihiro OGAWA1,2), Neng PU2), Hiroki KAWASE2), Sadayoshi MURAKAMI3), Mitsutaka ISOBE1,2), Masaki OSAKABE1,2) and the LHD Experimental Group1)
1)
National Institute for Fusion Science, National Institutes of Natural Sciences, 322-6 Oroshi-cho, Toki 509-5292, Japan
2)
The Graduate University for Advanced Studies, 322-6 Oroshi-cho, Toki 509-5292, Japan
3)
Kyoto University, Kyoto-daigaku-Katsura, Nishigyo-ku, Kyoto 615-8520, Japan
(Received 11 December 2017 / Accepted 25 February 2018 / Published 10 April 2018)

Abstract

The confinement of neutral beam (NB)-injected fast ions has been investigated by the neutron intensity decay time (τn) after the short pulse NB injection called “NB-blip.” The Large Helical Device (LHD) has five NB injectors. NBI#1, #2, and #3 are tangential direction injectors with typical energy of 180 keV. NBI#4 and #5 are perpendicular direction injectors with typical energies of 60 keV and of 80 keV, respectively. In this experiment, NBI#1, #2, #3, and #4 each with the pulse width of 40 ms are injected into different configuration plasmas with various electron densities. The τn is analyzed with a 0-dimensional fast ion slowing down model. The loss of the fast ion increases significantly with decrease in the electron density. From the comparison of calculated and measured τn for different plasma configurations, the fast ion confinement is worst on the outward shifted plasma of Rax = 3.90 m. On the other hand, it seems that the fast ion confinement is best on the plasma of Rax = 3.74 m.

Keywords

fast ion confinement, NB-blip, neutron intensity decay time, neutron flux monitor, slowing down model

DOI: 10.1585/pfr.13.3402024

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