Resonant particle effects on finite Larmor radius stabilization

It is shown that the threshold for instability of a one-dimensional Vlasov-fluid screw pinch is identical to that in ideal magnetohydrodynamics, for arbitrary ion gyroradius. That is, there is no absolute finite Larmor radius stabilization, although the growth rates for the Vlasov-fluid model can be much lower. It is the ions in resonance with the real part of the mode frequency which are responsible for maintaining the instability beyond the value of ρi/a for which ’’finite Larmor radius stabilization’’ would have occurred. An analytical expression for the growth rate near the marginal point is derived using the finite Larmor radius expansion. The expression exhibits the expected scaling with β and Larmor radius.