Plasma Physics and Controlled Nuclear Fusion Research

o;oNLINEAR TOROIDAL PLASMA DYNAMICS BY REDUCED FLUID MODELS. . Fluid models are presented which generalize reduced MHD by allowing for compressibility, Finite Larmor Radius, and long mean free path in toroidal geometry. The Hamiltonian structure of the models leads to a generalized energy principle for determining linear and nonlinear MHD stability of uilibria with flows and Finite Larmor Radius effects. Neoclassical effects from the long mean free ;Ih lead to new dissipative terms giving rotation damping, bootstrap currents and the Ware pinch. Rotation damping from non-ambipolar transport in stellarators can lead to self-consistent plasma currents'. .. wl1ich strongly reduce or "heal" steady-state magnetic stochasticity (e.g., from coil errors or pfirsch-Schliiter currents). The bootstrap current in tokamaks causes the growth of nonlinear magnetic isllUlds in the Rutherford regime. Thus, otherwise stable moderate mode number islands can potentially overlap, with serious detriment to confinement. INTRODUCTION We present models that generalize reduced MHD by allowing for compressibility, Finite Larmor Radius, and long mean free path. The Hamiltonian structure of the models leads to a significantly generalized energy principle. , Applications include linear and nonlinear instabilities and results regarding self·consistent magnetic stochasticity. 1. MORE REALISTIC FLUID MODELS A. COllventional high f3 reduced MHD[l] contains three fields: the poloidal flux function "p, a velocity stream function r/>, and pressure p. To allow for t compressible flows, we add parallel velocity. Previous Alfvenic normalizations are used[l]. FLR terms enter proportional to a parameter 6, defined so that. the normalized diamagnetic velocity (cT/neB)z X "Vn/evA is equal to 6£ X "Vp. We also define [Ql' Q2] = Z • "VQl X "VQ2, "VIIQ = ~ ["p, Q], F = ¢> + k6p, W = "Vi F, J = "Vi"p, with k = Ti/Te • The conserved energy is