Electron density profile and turbulence in toroidal plasmas

Tanaka, Kenji*; Takenaga, Hidenobu; Muraoka, Katsunori*; Michael, C.*; Vyacheslavov, L. N.*; Yokoyama, Masayuki*; Yamada, Hiroshi*; Murakami, Sadayoshi*; Wakasa, Arimitsu*; Kawahata, Kazuo*; Tokuzawa, Tokihiko*; Akiyama, Tsuyoshi*; Narihara, Kazumichi*; Yamada, Ichihiro*; Yoshinuma, Mikiro*; Ida, Katsumi*; Tamura, Naoki*; Oyama, Naoyuki; Urano, Hajime; Kamada, Yutaka

In order to understand mechanisms for determining density profiles in toroidal plasmas, density profiles were compared in JT-60U tokamak and LHD helical plasmas. Transport theory indicates that neoclassical transport is enhanced in helical plasmas with low collisionality due to helical ripple. In JT-60U plasmas, density peaking increased with decreasing the collisionality. In LHD plasmas for magnetic axis (Rax) of 3.5m with small effective helical ripple, density peaking slightly increased with decreasing the collisionality as similar to that in tokamak plasmas. On the other hand, in LHD plasmas for Rax3.6m with relatively large effective helical ripple, density profile became hollow as the collisionality decreased. Different turbulence structures are observed for Rax=3.5m and Rax=3.6m in LHD plasmas. Turbulence propagated towards electron diamagnetic direction for Rax=3.5m and towards ion diamagnetic direction for Rax=3.6m. This difference could be related to the difference of density profiles, as well as difference of neoclassical transport. Furthermore, when density decreased in the core region due to increase of electron temperature, it was found that turbulence was first modified in the edge region and then in the core region.