Magnetohydrodynamic-activity-induced toroidal momentum dissipation in collisionless regimes in tokamaks

It is shown that in the presence of magnetohydrodynamic (MHD) activities, such as resistive wall mode, the toroidal symmetry in tokamaks is broken. This results from the modification on |B|, and the variation of |B| on the distortion of the magnetic surface due to the MHD activities. Here, B is the magnetic field. The toroidal plasma viscosity in the collisionless regime for the nonresonant MHD modes is calculated. It scales like (δB/|B|)2 with δB, the typical magnitude of the perturbed magnetic field strength. The theory is applied to determine the toroidal flow speed in the presence of these modes.