Anisotropic pressure, transport, and shielding of magnetic perturbations

The effect on a tokamak of applying a nonaxisymmetric magnetic perturbation δB is computed. An equilibrium with scalar pressure p yields zero net radial current, and therefore zero torque. Thus, the usual approach, which assumes scalar pressure, is not self-consistent, and masks the close connection that exists between that radial current and the in-surface currents, which provide shielding or amplification of δB. Here, the pressure anisotropy, p∥,p⊥≠p, and from this, both the radial and in-surface currents, are analytically computed. The surface average of the radial current recovers earlier expressions for ripple transport, while the in-surface currents provide an expression for the amount of self-consistent shielding the plasma provides.