Speaker
Mr
Hiromi Takahashi
(Japan)
Description
Realization of high-T_i plasmas is one of the most important issues in helical plasmas, which have an advantage for steady-state operation comparison with tokamak plasmas. Since 2010, newly installed perpendicular-NBI with the beam energy of 40 keV has been operational in the Large Helical Device (LHD) and the total-heating power of perpendicular-NBIs increased from 6 MW to 12 MW. Such low-energy NBIs are effective for ion heating and enabled us to achieve a higher T_i than that obtained previously. In the last experimental campaign, ICRF-discharge cleaning was adopted to reduce particle recycling from the wall. As a result, NBI-heating-power profile became peaked and the density-normalized ion heating power in the core region increased by 18% and the central T_i of 7 keV, which is the world’s highest value for helical devices, was successfully achieved as the new record in the LHD.
In the LHD, high-T_i plasmas have been realized in combination with a carbon pellet. The kinetic-energy confinement was improved by a factor of 1.5 after the pellet injection. In the high-T_i phase, a flat or hollow profile in the electron density has been observed. This is the different characteristics from PEP mode investigated in Tokamaks. After the pellet injection, the central T_i, the gradient of T_i and that of the toroidal-flow velocity at the core region clearly increased indicating the formation of the ion-internal-transport barrier. In the high-T_i phase, reduction of the thermal diffusivity over the wide region was observed. In the core region, the time constant of the improvement of the ion-heat transport was found to be larger than that in the peripheral region. The toroidal-momentum transport was also improved accompanied with the reduction of the thermal diffusivity and the Prandtl number ignoring the intrinsic torque was close to unity. However, the confinement improvement was temporal and the gradient of T_i gradually decreased. Similarly, the toroidal-momentum transport went back to the low-confinement state in the latter phase of the discharge. Decrease of the negative radial electric field and increase of the density fluctuation were also observed in the phase.
Country or International Organization of Primary Author
Japan
Primary author
Mr
Hiromi Takahashi
(Japan)
Co-authors
Dr
Akihiro Shimizu
(National Institute for Fusion Science)
Dr
Arimitsu Wakasa
(Departement Nuclear Engineering, Kyoto University)
Dr
Chihiro Suzuki
(National Institute for Fusion Science)
Dr
Haruhisa Nakano
(National Institute for Fusion Science)
Dr
Hayato Tsuchiya
(National Institute for Fusion Science)
Dr
Hiroe Igami
(National Institute for Fusion Science)
Dr
Hiroshi Kasahara
(National Institute for Fusion Science)
Prof.
Hiroshi Yamada
(National Institute for Fusion Science)
Dr
Ichihiro Yamada
(National Institute for Fusion Science)
Prof.
Katsumi Ida
(National Institute for Fusion Science)
Dr
Katsunori Ikeda
(National Institute for Fusion Science)
Dr
Katsuyoshi Tsumori
(National Institute for Fusion Science)
Prof.
Kazumichi Narihara
(National Institute for Fusion Science)
Dr
Kenichi Nagaoka
(National Institute for Fusion Science)
Dr
Kenji Saito
(National Institute for Fusion Science)
Dr
Kenji Tanaka
(National Institute for Fusion Science)
Dr
Lee Hyungho
(University of Science and Technology)
Dr
Masaki Nishiura
(National Institute for Fusion Science)
Dr
Masaki Osakabe
(National Institute for Fusion Science)
Dr
Masanori Nunami
(National Institute for Fusion Science)
Dr
Masashi Kisaki
(National Institute for Fusion Science)
Dr
Masayuki Yokoyama
(National Institute for Fusion Science)
Dr
Mikiro Yoshinuma
(National Institute for Fusion Science)
Dr
Motoshi Goto
(National Institute for Fusion Science)
Dr
Naoki Tamura
(National Institute for Fusion Science)
Prof.
Osamu kaneko
(National Institute for Fusion Science)
Dr
Ryosuke Seki
(National Institute for Fusion Science)
Prof.
Ryuhei Kumazawa
(National Institute for Fusion Science)
Dr
Sadatsugu Muto
(National Institute for Fusion Science)
Dr
Sadayoshi Murakami
(Departement Nuclear Engineering, Kyoto University)
Dr
Seikichi Matsuoka
(National Institute for Fusion Science)
Prof.
Shigeru Morita
(National Institute for Fusion Science)
Prof.
Shin Kubo
(National Institute for Fusion Science)
Dr
Shinsuke Satake
(National Institute for Fusion Science, Japan)
Prof.
Takashi Mutoh
(National Institute for Fusion Science)
Prof.
Takashi Shimozuma
(National Institute for Fusion Science)
Dr
Takeshi Ido
(National Institute for Fusion Science)
Dr
Tetsuo Seki
(National Institute for Fusion Science)
Prof.
Yasuhiko Takeiri
(National Institute for Fusion Science)
Dr
Yasuo Yoshimura
(National Institute for Fusion Science)
