STUDIES OF GLOBAL STABILITY OF FIELD-REVERSED CONFIGURATION PLASMAS USING A RIGID-BODY MODEL

Global stability of field-reversed configuration (FRC) plasmas has bee n studied using a simple rigid body model in the parameter space of s (the ratio of the separatrix radius to the average ion gyro-radius) an d plasma elongation E (the ratio of the separatrix length to the separ atrix diameter). Tilt stability is predicted, independent of s, for FR C's with low E (oblate), while the tilt stability of FRC's with large E (prolate) depends on s/E. It is found that plasma rotation due to io n diamagnetic drift can stabilize the tilt mode when s/E less than or similar to 1.7. The so-called collisionless ion gyro-viscosity also is identified to stabilize tilt when s/E less than or similar to 2.2. Co mbining these two effects, the stability regime broadens to s/E less t han or similar to 2.8, consistent with previously developed theories. A small additional rotation (e.g., a Mach number of 0.2) can improve t ilt stability significantly at large E. A similar approach is taken to study the physics of the shift stability. It is found that radial shi ft is unstable when E<1 while axial shift is unstable when E>1. Howeve r, unlike tilt stability, gyro-viscosity has little effect on shift st ability. (C) 1998 American Institute of Physics. [S1070-664X(98)03110- 3].