Measurements of Plasma Rotation using Spectroscopic Method in the HYBTOK-II Tokamak with DED

Radial electric field and plasma rotation play an important role in formation of transport barrier. The effects of edge stochasticity produced by Dynamic Ergodic Divertor (DED) on tokamak plasma rota- tion were studied. Helium plasma rotations were measured by passive spectroscopic method, and sponta- neous toroidal rotation in the co-current direction was observed. With 3 kHz DED, both toroidal and pol- oidal rotation velocities decreased. On thermonuclear fusion research, it is concern that the serious damage of plasma-facing components as a result of large heat flux to the walls due to disruption or Edge Localized Modes. The method of externally-applying magnetic perturbation field to plasma periphery region, called Ergodic Divertor (ED), was proposed as a one of the solutions on tokamak device. ED is based on the modification of the particle and/or heat transport proper- ties in the stochastic layer arisen by magnetic island's overlap which is caused by helical magnetic perturbation induced by current conducting in the coil wound helically on the vacuum vessel. ED has achieved good results such as electron temperature reduction at plasma edge region (1). ED has been developed to Dynamic ED (DED), where "dynamic" means that applied field is rotating toroidally and poloidally, with potential of controlling plasma rota- tion. To establish good confinement of plasma at edge region and MHD stability, plasma rotation velocity and radial electric field shear are thought as key parameters (2). To control plasma rotation, jr1xBt torque, where jr1 is shielding current against rotating magnetic field, works as net momentum input. The modified radial electric field caused by ambipolarity in the stochastic region affects plasma rotation (3,4). In order to investigate the effects of perturbation field on plasma rotation, plasma rotation velocities and radial electric field have been measured by passive spectro- scopic method using line emission from singly ionized helium and by triple probe, respectively, in the small to- kamak HYBTOK-II.