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Report No.

Particle transport in LHD and comparisons with tokamaks

Tanaka, Kenji*; Takenaga, Hidenobu; Muraoka, Katsunori*; Urano, Hajime; Michael, C.*; Vyacheslavov, L. N.*; Yokoyama, Masayuki*; Yamagishi, Osamu*; Murakami, Sadayoshi*; Wakasa, Arimitsu*; LHD Experimental Group*

In order to understand particle transport systematically in toroidal plasmas, a density profile was compared in LHD helical and JT-60U tokamak plasmas. In large tokamak devices such as JT-60U, the density profile is always peaked and the peaked density profile can be explained based on outward diffusion flux and inward convection flux driven by microinstability. A peaking factor of the density profile was increased with decreasing collisionality. On the other hand, the density profile was changed from peaked one to hollow one depending on discharge conditions in LHD. The hollow density profile can be explained based on outward convection flux driven by neoclassical transport and inward diffusion flux driven by microinstability. In the configuration with a small helical ripple, where the neoclassical transport is reduced, the density profile tended to be peaked and dependence of the peaking factor on the collisionality was similar to that in tokamak plasmas. These results indicated that magnetic field ripple and microinstability are some of the main mechanisms determining the density profile.



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