Nonlinear plasma response and flow relaxation induced by resonant magnetic perturbation in Rutherford regime*

Externally applied non-axisymmetric magnetic fields such as error field and resonant magnetic perturbation (RMP) are known to influence the plasma momentum transport and dynamics through plasma response in a tokamak, whereas the evolution of plasma response itself strongly depends on the plasma flow as well. Such a nonlinear interaction between the two may be captured in a quasilinear model for the coupled system of torque balance and magnetic island evolution equations in the Rutherford regime. For a more complete and self-consistent account, we solve for the nonlinear plasma response and the associated flow relaxation induced by a single-helicity RMP for a circular-shaped limiter tokamak equilibrium with an initial uniform toroidal flow, using the initial-value, full MHD simulation code NIMROD. Time evolution of the parallel flow or "slip frequency'' profile and its asymptotic relaxation to steady state obtained from the NIMROD simulations qualitatively agree with the theory calculations. The difference suggests the nontrivial contribution of non-resonant or kink response to the flow dynamics.