Kinetic stabilization of fieldreversed configurations
Abstract
The tilt instability in fieldreversed configurations (FRC's) may be roughly divided into two categories, depending on the nature of the unstable eigenfunction. The internal tilt instability, which could also be called an n = 1 ballooning mode, is defined here to be an instability in which the displacement of the flux surfaces is confined to the closed region of magnetic field and the separatrix remains fixed in time. Since, for a fixed separatrix, the only destabilizing term in delta W is proportional to the pressure gradient times the parallel curvature of the magnetic field, the internal tilt could be considered a pressure driven mode. The external tilt is defined here to be an instability in which the entire closed field line FRC rotates rigidly about some axis perpendicular to the symmetry axis of the FRC. The external tilt results from magnetic interactions involving the toroidal plasma current. In spheromaks (at zero beta) the tilt instability is due to these same interactions, so in this sense the external mode might be considered current driven. However, since in FRC's the toroidal current comes solely from having finite plasma pressure, the distinction between pressure and current driven instabilities in FRC's is not meaningful (there is no parallel current). For oblate FRC's the eigenfunction of the external tilt is a rigid rotation of the closed field line FRC. For FRC's that are only moderately prolate the distinction between internal and external tilt modes is not clear, and the eigenfunction of the tilt mode may be a combination of internal and external displacements of the flux surfaces.
 Publication:

Presented at the 7th USJapan Workshop on Compact Toroids
 Pub Date:
 1985
 Bibcode:
 1985coto.work...12S
 Keywords:

 Eigenvectors;
 Magnetic Field Configurations;
 Magnetic Flux;
 Reverse Field Pinch;
 Rotation;
 Stabilization;
 Plasma Pressure;
 Pressure Gradients;
 Spheromaks;
 Toroidal Plasmas;
 Physics (General)