Shielding of resonant magnetic perturbations in the long mean-free path regime

Abstract

The effect of diamagnetic drifts and of long electron mean free path on the shielding of resonant magnetic perturbations by plasma rotation is investigated. The nature of the force exerted on a moving plasma by a resonant perturbation is qualitatively altered by both drift and long mean-free-path effects. The force is found to have three minima, each of which is a possible locus for discontinuous transitions in plasma velocity. Between these minima are two points where the force exerted by the perturbation is resonant. These points describe locked states where shielding is ineffective and a magnetic island will grow. They correspond to rotation velocities such that either the electrons or the ions are at rest in the frame of the perturbation. The ion root, however, is unstable.

Theory of tokamak disruptions

“…When the opening of islands at a rational surface q ¼ M= N is rapid, d I < ðm=r r Þd 2 d =4, high order resonant Fourier harmonics of the magnetic field, m=n ¼ jM=jN with j ) 1, are produced by thin current layers, 30 which are difficult to resolve in a simulation of the entire plasma though the effects could presumably be modeled if they were understood. If the thickness of the current layers is limited by the ion gyroradius, q s , a code that fully resolves the layers would have to retain toroidal mode numbers up to n $ R 0 =q s .…”

“…[29][30][31][32][33] Consequently, a quantitative answer for the resilience of the magnetic surfaces in a tokamak due to E Â B plasma rotation is given by the balance of the toroidal torque that can be produced by a magnetic perturbation and the toroidal torque carried by the cross-field viscosity, % m i nD v R 0 dx u =dr, where the effective viscous diffusion coefficient is generally assumed to be gyro-Bohm like,…”

Effect of resonant helical magnetic fields on plasma rotation

“…Recently, two fluids equations were utilized to study helical field penetration [8,9,14], including the linear study on the effect of a rotating helical field on plasma rotation [9]. As plasma rotation is very important for, e.g., the stability of the resistive wall modes, a better understanding of the experimental results given in Ref.…”

Magnetic Stochasticity in Gyrokinetic Simulations of Plasma Microturbulence

“…Magnetic reconnection occurs when the resonant component of A|| has a finite value at its rational surface [14]. GYRO employs field-line following coordinates in which the poloidal angle, θ, is used to label position along B.…”