Self-consistent simulation of torque generation by radial current due to fast particles

The generation of toroidal rotation due to the radial current torque induced by the charge separation is studied by using the one-dimensional multi-fluid transport code TASK/TX. Owing to the effect of the drift motion, the charge separation occurs as long as fast neutrals, typically from near-perpendicular NBI, are ionized. Coupling the TASK/TX code with the orbit-following Monte Carlo code (OFMC), we have shown that the toroidal rotation is driven due to the generation of the radial current j bulk flowing in the bulk plasma with the near-perpendicular NBI. The simulations have clarified that the NB on the equatorial plane drives the toroidal rotation most efficiently from the aspects of the collisional and j bulk × B torques. The j bulk × B torque becomes a major driver of the rotation in a high density plasma, replacing the collisional torque. In a steady state, the toroidal rotation driven by the j bulk × B torque is determined by the balance among the torque, the viscosity, the convection, the friction with neutrals and the loss of momentum due to charge exchange.