Dynamic Formation of Plasma Rotation in a Tokamak

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This research has been carried out to study (1) the dynamic formation process of the plasma rotation, (2) the relation between the plasma rotation and the sheared electric structure and (3) the formation process of the plasma rotation by the rotating helical magnetic field. So far, the following results has been obtained ;Fast response IGBT power supplies for Joule and vertical field coils have been installed in HYBTOK-II tokamak in order to produce target tokamak plasmas with good reproducibility. By the digital feedback control of the plasma horizontal position with a digital signal processor, flexible operation of the plasma current can be done very effectively, such as AC tokamak operation, rapid current rise and so on.Helical coils with m=6/n=1 as a main mode has been installed in HYBTOK-II and characteristics of the induced rotating helical field(RHF) in the present helical coil system were studied. When the direction of the helical field rotation is same as that of the plasma E × B rotation, the relative velocity decreases and the intensity of RHF is enhanced due to redistribution of the plasma current by island formation. When they are opposite, the intensity of RHF is remarkably dumped by the generation of the shielding current at the resonance layer.The electrode biasing is applied to modify the plasma rotation. In the preliminary experiment it is found that the modification of the plasma rotation by electrode biasing strongly affects the penetration of RHF and the dynamic relaxation of the RHF intensity has been observed just after the turn of the biasing.