Effect of Magnetic Curvature on the Drift-Cyclotron Instability

The effect of magnetic curvature on drift-cyclotron instabilities is examined. These instabilities, driven by the density gradient, are expected to be the most important electrostatic instabilities in well-thermalized (Maxwellian) plasmas. It is found for the flute mode, K∥ = 0, that a moderate amount of good (cusp-like) magnetic curvature stabilizes the longest wavelengths most likely to cause anomalous diffusion and shifts the unstable frequencies below the cyclotron frequency. Curvature does not stabilize the convective modes, K∥ ≠ 0, but these modes can be stabilized by avoiding resonance. Results are applied, speculatively, to average minimum-B fields, for which an additional ``communication'' criterion is necessary for stability.