Global Stability of the Field Reversed Configuration
Authors: E.V. Belova, S.C. Jardin, H. Ji, R.M. Kulsrud, W. Park, and M. Yamada
Date of PPPL Report: November 2000
Presented at: the 18th International Atomic Energy Agency's (IAEA) Fusion Energy Conference 2000 (FEC-2000) held in Sorrento, Italy, October 4-10, 2000. An unedited proceedings will be published by IAEA in electronic format (CD-ROM) only.
New computational results are presented which provide a theoretical basis for the stability of the Field Reversed Configuration (FRC). The FRC is a compact toroid with negligible toroidal field in which the plasma is confined by a poloidal magnetic field associated with toroidal diamagnetic current. Although many MHD modes are predicted to be unstable, FRCs have been produced successfully by several formation techniques and show surprising macroscopic resilience. In order to understand this discrepancy, we have developed a new 3D nonlinear hybrid code (kinetic ions and fluid electrons), M3D-B, which is used to study the role of kinetic effects on the n = 1 tilt and higher n modes in the FRC. Our simulations show that there is a reduction in the tilt mode growth rate in the kinetic regime, but no absolute stabilization has been found for s bar less than or approximately equal to 1, where s bar is the approximate number of ion gyroradii between the field null and the separatrix. However, at low values of s bar, the instabilities saturate nonlinearly through a combination of a lengthening of the initial equilibrium and a modification of the ion distribution function. These saturated states persist for many Alfvén times, maintaining field reversal.