Study of a helical axis heliotron

Wakatani, Masahiro; Nakamura, Yuji; Kondo, K.; Nakasuga, M.; Besshou, S.; Obiki, T.; Sano, F.; Hanatani, K.; Mizuuchi, T.; Okada, H.; Nagasaki, K.; Inoue, N.; Yokoyama, M.

doi:10.1088/0029-5515/40/3y/318

Cited by 66 publications

(78 citation statements)

References 5 publications

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“…The research program regarding Heliotron J (a low shear helical-axis heliotron having four periods, ι /2π = 0.557, R = 1.2 m, and a < 0.2 m) is focused on the establishment, characterization, and improvement of plasma confinement in the next-generation heliotron line [1,2]. The characterization of 70-GHz, 0.4-MW ECH plasma confinement in Heliotron J was studied with special regard to its magnetic configuration effects [3].…”

mentioning

confidence: 99%

Recent H-mode Results on ECH plasmas in Heliotron J

Sano

Mizuuchi

Nagasaki

et al. 2003

J. Plasma Fusion Res.

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Recent 70-GHz, 0.4-MW ECH experiments in Heliotron J have revealed the existence of the spontaneous confinement transition, like that of the H-mode, at rather low threshold line-averaged densities of 1.2-1.6 × 10 19 m -3 . The transition was discovered in two edge-iota windows: one is 0.54 < ι (a)/ 2π < 0.56 at separatrix discharge plasmas and the other is 0.62 < ι (a)/2π < 0.63 at partial walllimiter discharge plasmas. The energy confinement time for the separatrix discharge plasmas was found to be enhanced beyond the normal ISS95 scaling in the transient H-mode phase, being 50% longer than that in the "before transition" phase. Keywords:heliotron, stellarator, H-mode, transition phenomena, confinement improvementThe research program regarding Heliotron J (a low shear helical-axis heliotron having four periods, ι /2π = 0.557, R = 1.2 m, and a < 0.2 m) is focused on the establishment, characterization, and improvement of plasma confinement in the next-generation heliotron line [1,2]. The characterization of 70-GHz, 0.4-MW ECH plasma confinement in Heliotron J was studied with special regard to its magnetic configuration effects [3]. The experiments revealed that the energy confinement characteristics in the normal confinement mode (T e < 1.5 keV, T i CX < 0.2 keV, -n e = (0.2 -3.0) × 10 19 m -3 , W p diam < 3 kJ, and B 0 < 1.5 T) indicate the existence of "good" confinement plasmas whose energy confinement time becomes 1.5-2 times longer than the ISS95 scaling [4]. At present, it is not clear whether these good confinement plasmas are essentially different from those of the traditional ISS95 scaling. Beside these good confinement plasmas, the spontaneous confinement improvement mode, like that of the H-mode, was author's e-mail: sano@iae.kyoto-u.ac.jp recently discovered during the ECH with strong gas puffing in two edge-iota windows. Figure 1 shows the time evolution of the observed H-mode behavior in which the sudden drops in both H α and SOL probe signals and the subsequent strong rises in both line-integrated density and diamagnetic energy content were observed at the H-mode transition. In the case of the vacuum edge iota ι (a)/2π = 0.542, the peak increment of the plasma energy content was about 70% while that in the case of ι(a)/2π = 0.623 was about 30%. These confinement improvements remained transient on an energy confinement timescale and the post-transition steady-state phase was not yet attained. ECE measurements revealed that, after the transition, the core electron temperature inside r/a < 2/3 slightly increased or was well maintained despite the strong increase in density. On the other hand, in the SOL region, Langmuir probe measurements revealed that, after the transition, the SOL density fluctuation also dropped in the fre-

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confidence: 99%

Recent H-mode Results on ECH plasmas in Heliotron J

Sano

Mizuuchi

Nagasaki

et al. 2003

J. Plasma Fusion Res.

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“…(5), we referred to the value of the commercially available stainless steel pipe for pressurized water that has the closest inner diameter. The thickness of the pipe is 10 mm at the position of which the transverse magnetic field has maximum, 6.1 T. The magnetic field is calculated by the finite volume current element code KMAG [6,7]. For simplicity, we ignore the effect of the change in the magnetic field along the toroidal direction (corresponding to the sections J-K and M-N).…”

Section: Geometry Of the Flow Channel Andmentioning

confidence: 99%

Estimation of the Pumping Power of the Liquid Metal Divertor REVOLVER-D for the LHD-Type Helical Fusion Reactor FFHR-d1

Goto

Miyazawa

2017

Plasma and Fusion Research

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The required pumping power for the liquid metal ergodic limiter/divertor REVOLVER-D (Reactor-oriented Effectively VOLumetric VERtical Divertor), which is considered as an optional divertor design for the LHDtype helical fusion reactor FFHR-d1, has been estimated with a consideration of the change in the strength of transverse magnetic field along the flow channel. It is found that the pressure drop and the required pumping power can be suppressed to an acceptable level by using insulated ducts.

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“…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-...…”

Section: Physics Of Heliotron J Confinementmentioning

confidence: 99%

“…The magnetic well configuration is one of the key advantages of Heliotron J in maintaining good confinement at high beta values. In addition, the magnetic well can satisfy the typical Mercier criterion up to <β> ∼ 4 % [8] in contrast to a value of <β> ∼ 2 % for Heliotron E. The primary goal of Heliotron J is to contribute to the physical understanding of configuration optimization of the heliotron line, although a similar low-shear concept with a magnetic well using modular coils was studied in W7-AS (R = 2.0 m, a = 0.2 m, B < 3 T) and will be further investigated in W7-X (R = 6.5 m, a = 0.65 m, B < 3 T) to develop a modular stellarator line originally based on quasi-helical symmetry [9]. Complementary experiments in Heliotron J and W7-X will be useful for the better understanding of the different optimization scenarios required for each line.…”

Section: Introductionmentioning

confidence: 99%

Physics of Heliotron J Confinement

Sano

Mizuuchi

Nagasaki

et al. 2010

Plasma and Fusion Research

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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-H transition), confinement improvement based on supersonic molecular beam injection (SMBI), magnetohydrodynamic (MHD) activity, edge plasma characteristics, including rotation of a filamentary turbulence structure, and plasma current control, including the electron cyclotron current drive (ECCD), the energetic-particle driven Alfvén eigenmodes, and related fast ion dynamics. The results are discussed in terms of the rotational transform ι/2π and the bumpiness ε b (or the effective helical ripple ε eff ). Control of these two parameters was experimentally demonstrated to be the key issue in determining the optimum performance of Heliotron J. The result confirms that the helical-axis heliotron provides a unique and high potential for exploiting an alternative and advanced path to future helical systems.

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Study of a helical axis heliotron

Cited by 66 publications

References 5 publications

Recent H-mode Results on ECH plasmas in Heliotron J

Recent H-mode Results on ECH plasmas in Heliotron J

Estimation of the Pumping Power of the Liquid Metal Divertor REVOLVER-D for the LHD-Type Helical Fusion Reactor FFHR-d1

Physics of Heliotron J Confinement

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