Feedback Stabilization of a Drift-Type Instability

Low-frequency electrostatic waves in a reflex discharge are stabilized by feeding an amplified and phase-shifted probe signal to a pair of plates at the discharge walls. The plates couple electrostatically to the $k_{\parallel }\approx 0$ drift-type modes and stabilize them, giving a modest increase in density. A root-locus diagram is devised to explain the observed features of the system response.