A Flute-like Plasma Instability Driven by Field Inhomogeneities

Abstract

We investigate the stability of ring-like plasma configurations with small Larmor radii, precessing axi-symmetrically in mirror machines. If the precession frequency increases with radius, such equilibria may be subject to a low frequency flute-like instability which is driven by field inhomogeneities rather than by the density gradient. The phase velocity of the unstable waves is twice that occurring in the case of the ordinary flute-instability. Though the physical situation is quite different from that of circular beams of charged particles, the driving mechanism shows a certain analogy to that of the negative mass instability. It is noteworthy, however, that in our case equilibria with a finite spread in the transverse particle energies may be less stable than those with zero energy spread.