Initial physics achievements of large helical device experiments

Motojima, O.; Yamada, H.; Komori, A.; Ohyabu, N.; Kawahata, K.; Kaneko, O.; Masuzaki, S.; Ejiri, A.; Emoto, M.; Funaba, H.; Goto, M.; Ida, K.; Idei, H.; Inagaki, S.; Inoue, Noriyuki; Kado, S.; Kubo, S.; Kumazawa, R.; Minami, Takashi; Miyazawa, J.; Morisaki, T.; Morita, S.; Murakami, S.; Muto, S.; Mutoh, T.; Nagayama, Y.; Nakamura, Yuji; Nakanishi, Hiroyuki; Narihara, K.; Nishimura, K.; Noda, N.; Kobuchi, T.; Ohdachi, S.; Oka, Y.; Osakabe, M.; Ozaki, T.; Peterson, B.J.; Sagara, A.; Sakakibara, S.; Sakamoto, R.; Sasao, H.; Sasao, M.; Sato, K.; Sato, Motoyasu; Seki, T.; Shimozuma, Τ.; Shoji, M.; Suzuki, H.; Takeiri, Y.; Tanaka, K.; Toi, K.; Tokuzawa, T.; Tsumori, K.; Tsuzuki, K.; Yamada, I.; Yamaguchi, S.; Yokoyama, M.; Watanabe, K.Y.; Watari, T.; Hamada, Y.; Matsuoka, K.; Murai, K.; Ohkubo, Κ.; Ohtake, I.; Okamoto, M.; Satoh, Shuichi; Satow, T.; Sudo, S.; Tanahashi, S.; Yamazaki, K.; Fujiwara, Masami; Iiyoshi, A.

doi:10.1063/1.873443

Cited by 175 publications

(57 citation statements)

References 13 publications

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“…This is partly due to the lack of appropriate diagnostics, and partly due to the smallness of the hitherto used stellarators. With the start of the large helical device (LHD) experiment with sophisticated diagnostics [10], we could first (we think) observe the island behavior in a stellarator in the presence of plasma.LHD [11,12] is a superconducting magnet system composed of an L 2͞M 10 helical coil and three pairs of poloidal coils. The currents in these coils are fed independently, allowing us to change the shape and position of the magnetic surfaces as well as the magnetic field strength on axis B ax up to 3 T. The plasmas we analyze in this Letter were produced in two magnetic configurations with different magnetic axis positions: R ax 3.75 and 3.6 m. The poloidal cross sectional views of magnetic field lines at a horizontally elongated section are shown for the R ax 3.6 and 3.75 m configurations in Figs.…”

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“…LHD [11,12] is a superconducting magnet system composed of an L 2͞M 10 helical coil and three pairs of poloidal coils. The currents in these coils are fed independently, allowing us to change the shape and position of the magnetic surfaces as well as the magnetic field strength on axis B ax up to 3 T. The plasmas we analyze in this Letter were produced in two magnetic configurations with different magnetic axis positions: R ax 3.75 and 3.6 m. The poloidal cross sectional views of magnetic field lines at a horizontally elongated section are shown for the R ax 3.6 and 3.75 m configurations in Figs.…”

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confidence: 99%

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Observation of the “Self-Healing” of an Error Field Island in the Large Helical Device

Narihara¹,

Watanabe²,

Yamada³

et al. 2001

Phys. Rev. Lett.

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It was observed that the vacuum magnetic island produced by an external error magnetic field in the large helical device shrank in the presence of plasma. This was evidenced by the disappearance of flat regions in the electron temperature profile obtained by Thomson scattering. This island behavior depended on the magnetic configuration in which the plasmas were produced. DOI: 10.1103/PhysRevLett.87.135002 PACS numbers: 52.55.HcExistence of a set of nested magnetic surfaces (magnetic configuration) is a prerequisite for almost all toroidal magnetic confinement devices [1]. In the tokamak, a magnetic configuration is generated by plasma current plus external coil currents, and hence the concept of a vacuum magnetic configuration does not exist. On the other hand, the stellarator, by its definition, possesses a vacuum magnetic configuration that is able to confine plasma just as Nature possesses a vacuum space-time that allows the existence of matter. This fact makes it easier in the stellarator than in the tokamak to study the interactions between the magnetic configuration and plasma such as the formation of topological defects and their reactions on the plasma behavior. The vacuum magnetic configuration of a stellarator is inevitably accompanied by topological defects such as magnetic islands and stochastic regions as a result of a weak violation of a helical symmetry. If these defects are large in size or numerous, they will deteriorate the plasma confinement considerably. This was a central issue in stellarator development. However, nowadays, we can make these topological defects small enough not to degrade the plasma confinement over a wide region by optimizing the coil-winding law [2]. Although the vacuum magnetic configuration problem was thus solved, the question whether a fairly good magnetic configuration is preserved in the presence of plasma has not yet been settled. Cary and Kotschenreuther [3] showed that sharply peaked currents near the island enhance or limit the island size, depending on whether the average curvature is bad or good. They also showed that in the hill region the islands overlap for arbitrary small beta b (kinetic pressure/magnetic pressure). Hegna and Bhattacharjee [4] generalized the above statement for higher b plasma with the result that the well/hill criterion should be replaced by the resistive interchange stability criterion. Hayashi et al. [5] computationally found that the vacuum magnetic surfaces of an L 2͞M 10 heliotron/torsatron configuration are, indeed, broken at high b, giving a more stringent limit on b than that imposed by equilibrium. Hayashi et al. [6] also discovered that as b increases the islands present in the vacuum heliac configuration diminish ("self-heal") and then reappear with the flipped phase at a higher b. Bhattacharjee et al. [7] formulated a theory to explain the above "self-healing" phenomenon. Hegna [8] further generalized the above theories to incorporate the effect of a bootstrap current. Since these theoretical and numerical predictions hav...

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confidence: 99%

Observation of the “Self-Healing” of an Error Field Island in the Large Helical Device

Narihara¹,

Watanabe²,

Yamada³

et al. 2001

Phys. Rev. Lett.

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“…It has a set of L = 2/M = 10 helical coils with a major radius of 3.9 m (Motojima et al 1999). Recent LHD experiments revealed that plasmas can be confined relatively well even under the magnetic configuration with vacuum magnetic axis position R ax = 3.6 m, which is considered unstable in the sense of Magnetohydrodynamic (MHD) instability.…”

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confidence: 99%

Vortical, toroidal and compressible motions in 3D MHD simulations of LHD

et al. 2006

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Abstract. Direct numerical simulation of fully three-dimensional, compressible and nonlinear magnetohydrodynamic equations in the Large Helical Device is carried out in combination with the passive particle simulation. In the simulation, strong vortical motions are excited by the pressure-driven instability and form the mushroom-like structures of pressure. It is shown by the passive particles analysis that the fluid volumes around the resonant magnetic surfaces experience finite compressibility and toroidal deformation, which are both excited by the strong vortical motions. The passive particles simulation helps us to investigate local structures even for low Fourier wavenumber modes.

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“…In this situation, a Tracer-Encapsulated Solid Pellet (TESPEL) [1,2] was developed to promote the impurity transport study in the magnetically-confined plasma. The impurity transport study with the TESPEL technology has been performed mainly in the Large Helical Device (LHD) [3,4] at the National Institute for Fusion Science (NIFS) in Japan, and is currently planned in the TJ-II stellarator [5] at the National Fusion Laboratory in the Research Center for Energy, Environment and Technology (CIEMAT) in Spain [6]. The TESPEL is a double-layered impurity pellet.…”

Section: Introductionmentioning

confidence: 99%

Creation of Impurity Source inside Plasmas with Various Types of Tracer-Encapsulated Solid Pellet

Tamura

Sudo

Suzuki

et al. 2015

Plasma and Fusion Research

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A Tracer-Encapsulated Solid Pellet (TESPEL) was developed for promoting an impurity transport study in a magnetically-confined plasma. One of the advantages of the TESPEL is that it can make a three-dimensionally localized impurity source in the plasma. This enables us to inject the tracer impurity inside or in the vicinity of the region of interest. Recently, a new-type TESPEL with a thinner outer shell has been developed in order to achieve a shallower deposition of the tracer impurity. With the TESPEL having the thinner shell, we have achieved about 4 cm shallower deposition of the tracer impurity, compared with the case of the conventional thick-shell type TESPEL with the same outer diameter of about 700 µm. Moreover, for the achievement of the further shallower deposition of the tracer impurity, we also developed the TESPEL with a tracer-impurity-doped thin shell. After the injection of the TESPEL with the tracer-impurity-doped thin shell, the line emissions from the highly-ionized doped impurity are clearly observed with a vacuum ultraviolet spectrometer, which clearly demonstrates its ability to carry the impurity as a new tool.

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Initial physics achievements of large helical device experiments

Cited by 175 publications

References 13 publications

Observation of the “Self-Healing” of an Error Field Island in the Large Helical Device

Observation of the “Self-Healing” of an Error Field Island in the Large Helical Device

Vortical, toroidal and compressible motions in 3D MHD simulations of LHD

Creation of Impurity Source inside Plasmas with Various Types of Tracer-Encapsulated Solid Pellet

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