Speaker
Dr
Shinji Kobayashi
(IAE, Kyoto Univ.)
Description
In this study, we report on the H-mode transition triggered by high-intensity gas puffing (HIGP) in NBI plasmas of Heliotron J. Heliotron J is a medium sized (R/a = 1.2/0.17m) helical-axis heliotron device with an L/M=1/4 helical coil, where L is the pole number of the helical coil and M is the pitch number. An H-mode transition has been observed in the high density NBI plasmas. In the H-mode phase, an improvement in the energy confinement time normalized to that of the international stellarator scaling law around 2 has been achieved.
In the case when the H-mode transition occurs, the recovery of the stored energy is found after the stop of HIGP. The recovery phenomenon is similar to that of so-called "reheat mode" observed in CHS. During the applying HIGP, a bursting n =2 mode with f = 5-30 kHz appears until the occurrence of the H-mode transition. The density fluctuation with the burst frequency (f = 0.8-3 kHz), measured by beam emission spectroscopy (BES), propagates in the outward direction, which is synchronized with the H_alpha / D_alpha intensity. These observations indicate the particle exhaust phenomena. The time evolution of the density gradient in the peripheral region (r/a = 0.9) calculated by the BES signals suggests the repetition of the increase/decrease in the density gradient before the transition, indicating so-called "dithering" phenomena. At the timing of the H-mode transition, the density gradient increases along with the disappearance of the particle exhaust. After that, the formation of the steep density gradient is observed in the peripheral region (r/a = 0.8-1). In the case where the amount of HIGP is smaller than that when the H-mode transition occurs, the particle exhaust is not observed, although the reheat mode is found. In this case, the density gradient is smaller than that in the H-mode case.
This work was supported by JSPS Grant-in-Aid for Scientific Research (C) 15K06645.
| Country or International Organization | JAPAN |
|---|---|
| Paper Number | EX/P8-17 |
Primary author
Dr
Shinji Kobayashi
(IAE, Kyoto Univ.)
Co-authors
Dr
Akihiro Ishizawa
(Graduate School of Energy Science, Kyoto Univ)
Dr
Gavin WEIR
(Institute of Advanced Energy, Kyoto University)
Mr
Hirotsugu Matsuda
(Graduate School of Energy Science, Kyoto Univ)
Dr
Hiroyuki Okada
(Institute of Advanced Energy, Kyoto University)
Dr
Katsumi Ida
(National Institute for Fusion Science)
Prof.
Kazunobu Nagasaki
(Institute of Advanced Energy, Kyoto University)
Prof.
Kiyomasa WATANABE
(National Institute for Fusion Science)
Mr
Mitsuaki KIRIMOTO
(Graduate School of Energy Science, Kyoto Univ)
Mr
Naoki Kenmochi
(Graduate School of Energy Science, Kyoto Univ)
Dr
Ryohsuke Seki
(National Institute for Fusion Science)
Dr
Sadayoshi Murakami
(Departement Nuclear Engineering, Kyoto University)
Dr
Satoshi Yamamoto
(Institute of Advanced Energy, Kyoto University)
Dr
Shigeru Konoshima
(Institute of Advanced Energy, Kyoto University)
Dr
Shinichiro KADO
(Institute of Advanced Energy, Kyoto University)
Dr
Shinsuke OHSHIMA
(Institute of Advanced Energy, Kyoto University)
Dr
Takashi Minami
(Institute of Advanced Energy, Kyoto University)
Dr
Tatsuya Kobayashi
(National Institute for Fusion Science)
Dr
Tohru MIZUUCHI
(Institute of Advanced Energy, Kyoto University)
Mr
Xiangxun Lu
(Graduate School of Energy Science, Kyoto Univ)
Dr
Yasuhiro Suzuki
(National Institute for Fusion Science)
Mr
Yoshiaki Otani
(Graduate School of Energy Science, Kyoto Univ)
Prof.
Yousuke Nakashima
(Plasma Research Center, University of Tsukuba)
Prof.
Yuji Nakamura
(Graduate School of Energy Science, Kyoto Univ)
