High beta discharges with neutral beam injection in CHS

Okamura, S.; Matsuoka, K.; Nishimura, K.; Tsumori, K.; Akiyama, R.; Sakakibara, S.; Yamada, H.; Morita, S.; Morisaki, T.; Nakajima, N.; Tanaka, K.; Xu, J.; Ida, K.; Iguchi, H.; Lazaros, A.; Ozaki, T.; Arimoto, Hideki; Ejiri, A.; Fujiwara, Masami; Idei, H.; Kaneko, O.; Kawahata, K.; Kawamoto, T.; Komori, A.; Kubo, S.; Motojima, O.; Pustovitov, V. D.; Takahashi, C.; Toi, K.; Yamada, I.

doi:10.1088/0029-5515/35/3/i03

Cited by 47 publications

(18 citation statements)

References 21 publications

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“…With respect to the Shafranov shift, the studies in W7-AS and LHD, but also in CHS [16], have shown a good agreement with 3D equilibrium code calculations with VMEC, HINT and PIES. In particular, the partial optimization of the W7-AS configuration resulting in reduced Shafranov shift could be verified [1].…”

Section: Ms-313705 Final Papersupporting

confidence: 55%

“…Before start of LHD operation, beta values in the 1.5 -2 % range have been reported by several stellarator experiments including Heliotron-E [14], the Advanced Torsatron Facility ATF [15], the Compact Helical System CHS [16] and W7-AS. Here, we are focusing on more recent results from W7-AS and LHD.…”

Section: Progress Of High-β Operation In Stellarators / Helical Systemsmentioning

confidence: 98%

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Significance of MHD Effects in Stellarator Confinement

Weller

Sakakibara

Watanabe

et al. 2006

Fusion Science and Technology

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Substantial progress has been achieved to raise the plasma beta in stellarators and helical systems by high power neutral beam heating, approaching reactor relevant values [1][2][3]. The achievement of high-β operation is closely linked with configuration effects on the confinement and with magnetohydrodynamic (MHD) stability. However, the observed pressure gradients indicate some mitigation of the effects on the plasma confinement, presumably because of the high collisionality of high-β plasmas and island healing effects ). As far as operational limits by pressure driven MHD instabilities are concerned, only weak confinement degradation effects are usually observed, even in linearly unstable regimes.The impact of the results concerning high-β operation in W7-AS and LHD on the future stellarator programme will be discussed, including relations to tokamak research. Some of the future key issues appear to be: -the control of the magnetic configuration (including toroidal current control), -the modification of confinement and MHD properties towards the low collisional regime, -and the compatibility of high-β regimes with power and particle exhaust requirements to achieve steady state operation.

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Section: Ms-313705 Final Papersupporting

confidence: 55%

Section: Progress Of High-β Operation In Stellarators / Helical Systemsmentioning

confidence: 98%

Significance of MHD Effects in Stellarator Confinement

Weller

Sakakibara

Watanabe

et al. 2006

Fusion Science and Technology

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“…This density dependence is a feature of anomalous transport, because strong density dependence is also observed in the energy transport, which is governed by anomalous transport. In fact, the global energy confinement shows strong density dependence in CHS, 11 as predicted by LHD scaling 12 ( E ϭ0.17P abs The differences between the parallel viscosity in the original paper and the toroidal viscosity in this paper are discussed. The approximations made in the original paper were a replacement of the Fourier series with (1/M ) ϫ(n -"B/B) and the replacement of toroidal viscosity with parallel viscosity (B ϷB) and (B -"B)/BϷn -"B).…”

Section: Discussionmentioning

confidence: 65%

Comparison of toroidal viscosity with neoclassical theory

Ida

Nakajima

1997

Physics of Plasmas

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Toroidal rotation profiles are measured with charge exchange spectroscopy for a plasma heated with tangential neutral beam injection ͑NBI͒ in the Compact Helical System ͑CHS͒ heliotron/torsatron device ͓Ida et al., Phys. Rev. Lett. 67, 58 ͑1991͔͒ to estimate the toroidal viscosity. The toroidal viscosity derived from the toroidal rotation velocity shows good agreement with the neoclassical toroidal viscosity plus the perpendicular viscosity ( Ќ ϭ2 m 2 /s).

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“…A capability of high-␤ equilibrium is, therefore, expected for the CHS; the highest beta of 2% was achieved. 41 The CHS has a pair of four-turn windings of helical coils to generate its essential confinement field. The magnetic field configuration has a rotational symmetry of 45 degrees.…”

Section: B Compact Helical Systemmentioning

confidence: 99%

Experimental study of the bifurcation nature of the electrostatic potential of a toroidal helical plasma

et al. 2000

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The bifurcation nature of the electrostatic structure is studied in the toroidal helical plasma of the Compact Helical System ͑CHS͒ ͓K. Matsuoka et al., Proceedings of the 12th International Conference on Plasma Physics and Controlled Nuclear Fusion Research, Nice, 1988 ͑International Atomic Energy Agency, Vienna, 1989͒, Vol. 2, p. 411͔. Observation of bifurcation-related phenomena is introduced, such as characteristic patterns of discrete potential profiles, and various patterns of self-sustained oscillations termed electric pulsation. Some patterns of the electrostatic structure are found to be quite important for fusion application owing to their association with transport barrier formation. It is confirmed, as is shown in several tokamak experiments, that the thermal transport barrier is linked with electrostatic structure through the radial electric field shear that can reduce the fluctuation resulting in anomalous transport. This article describes in detail spatio-temporal evolution during self-sustained oscillation, together with correlation between the radial electric field and other plasma parameters. An experimental survey to find dependence of the temporal and spatial patterns on plasma parameters is performed in order to understand systematically the bifurcation property of the toroidal helical plasma. The experimental results are compared with the neoclassical bifurcation property that is believed to explain the observed bifurcation property of the CHS plasmas. The present results show that the electrostatic property plays an essential role in the structural formation of toroidal helical plasmas, and demonstrate that toroidal plasma is an open system with a strong nonlinearity to provide a new attractive problem to be studied.

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High beta discharges with neutral beam injection in CHS

Cited by 47 publications

References 21 publications

Significance of MHD Effects in Stellarator Confinement

Significance of MHD Effects in Stellarator Confinement

Comparison of toroidal viscosity with neoclassical theory

Experimental study of the bifurcation nature of the electrostatic potential of a toroidal helical plasma

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