STABILITY OF THE GAS-DYNAMIC TRAP

The description of stability of the gas dynamic trap is shown to be extremely sensitive to the nature of the boundary conditions. Two model boundary conditions in a moderately long mean-free-path limit are considered: insulating boundary conditions and conducting boundary conditions. The former boundary condition reproduces the magnetohydrodynamic (MHD) results of previous studies, where the outflow of ions contribute to the MHD stabilizing properties of the system. However, with conducting boundary conditions it is shown that the outflowing ions do not contribute to the system's stability. In this case, which is likely to be physically relevant, the MHD stabilizing term only comes from the electron pressure in the expansion region, and the gas dynamic trap would not be as stable as previously envisioned. The physical difference in these two boundary conditions is attributed to a passive feedback mechanism from the oscillating edge potentials that is only present in the insulating boundary case.