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(IC/P-07) Physics Design of Quasi-Axisymmetric Stellarator CHS-qa

S. Okamura¹⁾, K. Matsuoka¹⁾, S. Nishimura¹⁾, M. Isobe¹⁾, C. Suzuki¹⁾, A. Shimuzu¹⁾, K. Ida¹⁾, A. Fujisawa¹⁾, S. Murakami¹⁾, M. Yokoyama¹⁾, K. Itoh¹⁾, T. Hayashi¹⁾, N. Nakajima¹⁾, H. Sugama¹⁾, M. Wakatani²⁾, Y. Nakamura²⁾, W. Anthony Cooper^3)
 
1) National Institute for Fusion Science, Toki, Japan
²⁾ Graduate School of Energy Science, Kyoto University, Uji, Japan
³⁾ Centre de Recherches en Physique des Plasmas, Association Euratom/Confederation Suisse, EPFL, Lausanne, Switzerland

Abstract.  CHS-qa has been designed in the National Institute for Fusion Science for the purpose of finding the new direction of the plasma confinement for fusion. It is a low aspect ratio quasi-axisymmetric stellarator. The number of toroidal periods is two and the average aspect ratio is 3.2 with the vacuum rotational transform between 2/6 and 2/5. Designed values of the device are R = 1.5 m and B = 1.5 T. The advantage of this type of advanced stellarator is emphasized in the experimental scenario of finding the improved confinement since the low neoclassical viscosity for the plasma rotation is expected to allow various types of improved confinement modes observed in tokamaks. In addition, CHS-qa has the controllability of the configuration for the interdisciplinary area of the improved confinement study for the neoclassical internal transport barrier (NITB) found in CHS and tokamak type ITB. The maximum-J condition, which is favorable for the stabilization of the trapped particle instability, is also evaluated and the configuration flexibility is prepared for the study of its effect on the confinement.

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