Feedback Destabilization of Mirror Machines by Microinstabilities

Electron loss from the magnetic mirrors in the DCX-2 experiments is shown to lead to a coupling of a gyrofrequency instability and a normally stable $\nabla B$ drift wave. This coupling produces a new instability near the drift frequency and can lead to cross-field particle transport. The effect is predicted to occur in minimun-$B$ geometries and may be the mechanism responsible for the particle loss in several experiments.