Verification of role of neoclassical poloidal viscosity on transition to improved confinement mode in toroidal plasma

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The electrode biasing experiments were carried out in various magnetic configurations in the Large Helical Device (LHD) and the Heliotron J. The neoclassical poloidal viscosity was evaluated from the theory and the experiments. Especially in the LHD, the neoclassical poloidal viscosity was calculated using FORTEC-3D code, which includes the finite Larmor radius effect. The simulation enabled us to calculate the neoclassical poloidal viscosity with high accuracy. Both the experimental and theoretical viscosities obtained in the LHD and the Heliotron J were compared with those previously evaluated in TU-Heliac and the CHS. Consequently the experimental results show good agreement with the theoretical prediction. In addition to those results, we unexpectedly observed the burst like transition under the marginal biasing condition in the Heliotron J, which is new interesting physical phenomenon.