Nonlinear magnetohydrodynamic studies of the tilt mode in field-reversed configurations

A three-dimensional magnetohydrodynamic code has been used to study the nonlinear evolution of the tilt instability in a field-reversed configuration. The evolution of the mode has been followed through magnetic field reconnection to complete the loss of confinement, with no evidence of any nonlinear stabilizing effects. The influence of plasma rotation has also been investigated. It was found that while the mode remains unstable, its character changed at high rotation rates. It evolves from an internal mode with a very small displacement velocity at the separatrix, to an external mode with almost no radial component to the displacement velocity. Hall term effects were found to be capable of reducing the growth rate for small and elongated configurations, but again, a change in mode character was found to prevent the stabilization predicted in a previous analysis. Kinetic effects remain the most promising mechanism to explain the observed stability of current experiments.