Anisotropic pressure tokamak equilibrium and stability considerations

Abstract

Investigation of the effect of pressure anisotropy on tokamak equilibrium and stability is made with a magnetohydrodynamic model. Realistic perpendicular and parallel pressure distributions, P⊥(ψ,B) and P∥(ψ,B), are obtained by solving a one-dimensional Fokker–Planck equation for neutral beam injection to find a distribution function f (E,v∥/v) at the position of minimum field on each magnetic surface and then using invariance of the magnetic moment to determine its value at each point on the surface. The shift of the surfaces of constant perpendicular and parallel pressure from the flux surfaces depends strongly on the angle of injection. This shift explains the observed increase or decrease in the stability conditions. Estimates of the stabilizing effect of hot trapped ions indicate that a large fraction must be nonresonant and thus decoupled from the bad curvature before it becomes important.