Experimental investigation of lower hybrid current drive induced plasma rotation on the experimental advanced superconducting tokamak

Abstract

Rotation and its shear can reduce the magnetohydrodynamic instabilities and enhance the confinement. The LHCD has been proposed as a possible means of rotation driving on a future fusion reactor. Exploring the mechanisms of LHCD rotation driving on the current tokamaks can provide important reference for future reactors. On EAST, it was previously shown that 2.45 GHz LHCD can drive plasma toroidal rotation and the change of edge plasma rotation leads the co-current core rotation to increase. At higher frequency, 4.6 GHz lower hybrid wave can more effectively drive co-current plasma toroidal rotation. On EAST, at the lower current, the effects of different LHCD power on plasma toroidal rotation are analyzed. Higher power LHCD has a better driving efficiency. The effect of safety factor (<i>q</i>) profile on toroidal rotation is also presented. The LHCD can change the profile of safety factor due to current drive. It is found that when the power exceeds 1.4MW, the <i>q</i> profile remains unchanged and the rotation changes only very slightly with LHCD power, suggesting that the current profile is closely related to rotation. In order to further analyze the dynamic process of plasma toroidal rotation driven by lower hybrid current drive on EAST, the toroidal momentum transport due to LHCD is deduced by using the modulated LHCD power injection. Based on the momentum balance equation, the toroidal momentum diffusion coefficient (<i>χ</i><i>_φ</i>) and the toroidal momentum pinch coefficient (<i>V</i>_pinch) are obtained by the method of separation of variables and Fourier analysis for the region where the external momentum source can be ignored. It is found that the momentum diffusion coefficient (<i>χ</i>_<i>φ</i>) and momentum pinch coefficient (<i>V</i>_pinch) tend to increase from the core to the outer region. This is consistent with the characteristic that the toroidal rotation velocity first changes in the outer region and then propagates to the core when the toroidal rotation is driven by LHCD.