Progress summary of LHD engineering design and construction

Abstract

In March 1998, the LHD project finally completed its eight year construction schedule. LHD is a superconducting (SC) heliotron type device with R = 3.9 m, ap = 0.6 m and B = 3 T, which has simple and continuous large helical coils. The major mission of LHD is to demonstrate the high potential of currentless helical-toroidal plasmas, which are free from current disruption and have an intrinsic potential for steady state operation. After intensive physics design studies in the 1980s, the necessary programmes of SC engineering R&D was carried out, and as a result, LHD fabrication technologies were successfully developed. In this process, a significant database on fusion engineering has been established. Achievements have been made in various areas, such as the technologies of SC conductor development, SC coil fabrication, liquid He and supercritical He cryogenics, development of low temperature structural materials and welding, operation and control, and power supply systems and related SC coil protection schemes. They are integrated, and nowadays comprise a major part of the LHD relevant fusion technology area. These issues correspond to the technological database necessary for the next step of future reactor designs. In addition, this database could be increased with successful commissioning tests just after the completion of the LHD machine assembly phase, which consisted of a vacuum leak test, an LHe cooldown test and a coil current excitation test. These LHD relevant engineering developments are recapitulated and highlighted. To summarize the construction of LHD as an SC device, the critical design with NbTi SC material has been successfully accomplished by these R&D activities, which enable a new regime of fusion experiments to be entered.

Identification of MHD Mode Structure using ECE and SX Measurements

“…This study was performed at the LHD [1]. The MHD fluctuations were measured mainly by MP [6], SX detector arrays [7] and radiometer of ECE [5].…”

“…In the Large Helical Device (LHD) [1], some magnetohydrodynamic (MHD) modes, including the interchange-type instability, excited in the edge region of a torus plasma have been observed in the high-beta regime [2], which does not lead to disruptive discharge termination. However, the instability is considered to be related to the decision mechanism of the achieved achieved beta values [3].…”

Recent Fusion Research in the National Institute for Fusion Science

“…scale superconducting magnets to enable advanced studies of net-current-free plasmas [1,2]. The major goal of the LHD experiment is to demonstrate the high performance of helical plasmas in a reactor relevant plasma regime for verifying the potential capability of a fusion reactor.…”

Physics of Heliotron J Confinement

“…Fumimichi SANO, Tohru MIZUUCHI, Kazunobu NAGASAKI, Kiyoshi HANATANI, Hiroyuki OKADA, Yuji NAKAMURA 1) , Takashi MINAMI, Shinji KOBAYASHI, Satoshi YAMAMOTO, Shigeru KONOSHIMA, Shinsuke OHSHIMA 2) , Masaki TAKEUCHI, Yoshiyuki IJIRI, Keiji YAGUCHI, Tohru SENJU, Masashi SHIBANO, Kiyoshi TOHSHI, Kinzou SAKAMOTO, Akinobu MATSUYAMA 1) , Kiyofumi MUKAI 1) , Keishi MINAMI 1) , Shintarou KISHI 1) , Hyunyong LEE 1) , Yu TAKABATAKE 1) , Hiroaki YASHIRO 1) , Kento YAMAMOTO 1) , Kohta NOMURA 1) , Masashige SUWA 1) , Hayao YOSHINO 1) , Sadayoshi MURAKAMI 3) , Takashi MUTOH 4) , Yasuhiko TAKEIRI 4) , Kenichi NAGAOKA 4) , Shoichi OKAMURA 4) , Kiyomasa Y. WATANABE 4) , Masayuki YOKOYAMA 4) , Yasuhiro SUZUKI 4) , Yasuo YOSHIMURA 4) , Shin NISHIMURA 4) , Naoki TAMURA 4) , Satoru SAKAKIBARA 4) , Gen MOTOJIMA 4) , Nobuhiro NISHINO 5) , Takeshi FUKUDA 6) , Yousuke NAKASHIMA 7) , Zhen FENG 8) , Qingwei YANG 8) , Angela FERNÁNDEZ 9) , Alvaro CAPPA 9) , Victor TRIBALDOS 9) , Boyd D. BLACKWELL 10) and Viktor V. CHECHKIN 11) Institute This paper reviews the results of an experimental study undertaken in Heliotron J over the past few years to explore the physics design base for a new concept of a helical-axis heliotron. Measurements of electron cyclotron resonance (ECR)/neutral beam injection (NBI)/ion cyclotron range of frequencies (ICRF) heating plasmas have been made for understanding global energy confinement in connection with the international stellarator scaling law (ISS04), spontaneous confinement improvement (L-...…”

“…For effective particle confinement in earlier planar-axis heliotrons, such as Heliotron E (R = 2.2 m, a = 0.2 m, B < 2.0 T) [3], drift optimization was realized by an inward magnetic axis shift while the edge magnetic hill region was expanded [4]. The large helical device (LHD) (R = 3.9 m, a = 0.6 m, B < 3.0 T) [5] also follows the same principle of drift optimization. The high shear common in such devices provides a stabilizing term for MHD instability.…”