Autoresonant control of a pre-excited diocotron mode

A new method for the manipulation of a pre-excited l=1 diocotron mode in a pure electron plasma in a Malmberg-Penning trap is proposed and analyzed. The plasma is passively coupled to an external oscillatory circuit with slowly varying parameters. A threshold on the coupling strength is derived beyond which the plasma is continuously self-phase-locked to the external circuit. In the case of a linearly chirped circuit frequency, this autoresonant plasma can be driven to the wall, and in the case of a chirped sinusoidal variation of the circuit frequency, the plasma can be driven to the center of the trap. Derived thresholds on the coupling strength are in good agreement with simulations. Unlike conventional feedback mechanisms, autoresonant phase locking is a consequence of the nonlinearity of the system.