Ion heating/transport characteristics of the merging startup plasma scenario in the TS-6 spherical tokamak

Abstract

Here we report ion heating/transport characteristics of merging startup scenario in the TS-6 spherical tokamak. In addition to the previously investigated impulsive heating process during magnetic reconnection, here we also focused on a longer time scale response of ion temperature profile both during and after merging including the semi-steady plasma confinement phase. During magnetic reconnection, (i) ion temperature profile forms poloidally asymmetric profile around the X-point at the initiation phase and (ii) radially asymmetric higher deposition is obtained in the high field side. After merging, (iii) the radially asymmetric double-peak structure is affected by parallel heat conduction and is aligned with field lines, but it does not simply become flux function in microsecond time scale: inboard/outboard asymmetry lasts even in the semi-steady confinement phase. (iv) Under the influence of low aspect ratio configuration, there is 2~3 times higher toroidal field in the high field side on a same closed flux surface, characteristic asymmetry of inboard/outboard ion temperature has experimentally been found for the first time.