Shielding of resonant magnetic perturbations by rotation

Magnetic perturbations that drive islands are shielded from a rotating plasma by either a torque limit or an equilibrium limit. The physics of the shielding is given in a simple slab model along with the mechanism by which the shielding currents are maintained. Shielding currents in a channel of width Δ are damped by a resistance η/Δ with η the resistivity. If an island is shielded in a nearly ideal plasma, η/Δ=(μ0/π)VpAM2p with VpA the poloidal Alfvén speed, Mp≡v⊥/VpA, and v⊥ the speed of the cross-field flow at the resonance surface.