Stabilization of the Modified Negative Mass Instability

Previous studies of the resonant, modified negative mass instabilities in finite mirror-confined plasmas with highly anisotropic velocity distributions have shown that, at least when the bounce harmonic structure is ignored, a small thermal spread in the pitch-angle or energy distribution does not stabilize the modes. Bounce harmonic effects with no thermal spread have been shown to introduce new unstable modes. Combining the bounce and thermal spreading effects. It is found that the negative mass modes are all stabilized if ηΔ ≡ Δ2Ω0/ωb>0.77, where Δ∼(T‖/T⊥)1/2 is the thermal spread (half-width at half-maximum) in the pitch-angle distribution, Ω0 is the minimum gyrofrequency, and ωb is the average bounce frequency.