Toroidal rotation profiles under the influence of fast-ion losses due to toroidal field ripple

Honda, Mitsuru; Takizuka, Tomonori; Fukuyama, Atsushi*; Yoshida, Maiko; Ozeki, Takahisa

Characteristics of toroidal rotation profiles in tokamak plasmas are studied under the influence of fast-ion losses due to a toroidal field (TF) ripple by using a one-dimensional multi-fluid transport code, TASK/TX. When a neutral beam (NB) is injected into a plasma, a part of fast ions is lost due to the effect of the TF ripple. The radial current then flows inward in the bulk plasma to keep quasi-neutrality and it exerts a torque on the plasma in the direction opposite to the plasma current. A parametric survey of the toroidal rotation driven by this torque is conducted to quantify the sensitivity to various externally-controllable sources such as a co-tangential NBI power. In the case of a larger ripple amplitude, it is observed that the counter-toroidal rotation develops near the periphery of the plasma as an increase in the co-NBI input power while the co-toroidal rotation velocity on the magnetic axis reaches a maximum value at a certain NBI power. This torque can be mitigated by increasing a gas puff rate. An increase in the plasma current also leads to the reduction in the counter rotation induced by ripple.