Active control of the ion-resonance instability in a trapped pure electron plasma

The fundamental diocotron mode in a pure electron plasma confined in a Malmberg-Penning trap is destabilized when a small population of positive charges is produced (transient ion resonance instability). The electron column undergoes a bulk rotation around the axis of the trap (m = 1 diocotron mode) with an increasing offset, until it reaches the confining walls, loosing particles. The instability has been analyzed using both optical and electrostatic diagnostics, and has been controlled by the application of a proper external electric field. This technique is effective in removing the instability and increasing the plasma meanlife.