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Abstract
We have investigated several aspects of the semi-collisional modes in magnetically confined high temperature plasmas. Kinetic effects associated with finite ion Larmor radius (FLR), which can significantly modify the conventional resistive magnetohydrodynamic (MHD) results are studied analytically. First, in a sheared slab geometry, the effects of transition from the unmagnetized ion response in the resistive region to the magnetized ion response in the ideal MHD region as well as the effects of diamagnetic drift frequencies ((omega)(,*)) are studied in detail. The resistive kinetic Alfven modes are found to be damped with the damping rates proportional to (log (nu)(,ei))('-1) with the corresponding eigenfrequencies approaching a finite real value in the small resistivity limit. The drift-tearing modes are found to be predominantly electromagnetic and mainly governed by the electron parallel dynamics. We have also investigated FLR effects on the m = 1 resistive internal kink modes. For the resistive-g modes, finite-(omega)(,*) effects reduce the growth rate considerably. However, FLR effects enhance the growth rate over the collisional value by a logarithmic factor, (TURN)log((rho)(,i)/L(,r)). (Here, (rho)(,i), and L(,r) are, respectively, the ion Larmor radius and resistive layer width.) In a cylindrical geometry, the semi-collisional drift-interchange modes are studied using the cold ion model. Both analytical and numerical results show that the modes can be completely stabilized by the perpendicular resisitivity for a moderate value of (omega)(,*e). Finally, we have studied the drift-interchange and drift-tearing modes in a toroidal geometry with cold ions. The ballooning mode representation and a flux-surface averaging method are employed to obtain the ordinary differential eigenmode equations of interest. For the semi-collisional drift-interchange modes, the same qualitative results as the cylindrical case are obtained. Meanwhile, for the semi-collisional drift-tearing modes, ion sound effects as well as the good average curvature lead to stabilizing effects characterized by (DELTA)(,c) which is independent of the resistivity and is associated with the tearing instability condition given by (DELTA)' > (DELTA)(,c) > 0.
