Generation and Active Control of Coherent Structures in Partially-Neutralized Magnetized Plasmas

Abstract

Penning-Malmberg (electro-magnetostatic) traps represent a great laboratory for the investigation of collective phenomena in plasmas and fluids, e.g., two-dimensional fluid dynamics and turbulence. As such they are usually exploited to trap single-species plasmas, which facilitates the diagnostics and manipulation of their dynamics as well as equilibrium states. Yet in some of the most advanced and challenging applications, such as sympathetic cooling, formation of ordered structures (crystals) or neutral antimatter, simultaneous confinement of multiple species, possibly with opposite sign of charge, is required, which complicates the plasma evolution and enhances instability mechanisms. We review a collection of experimental investigations focusing on the generation of an electron plasma by means of a radio-frequency (RF) electric field. The in-trap generation scheme also implies the presence of positive ions, and the complex dynamics of the two plasma components in the presence of a relatively strong RF drive gives rise to a wealth of new features with respect to single-species plasmas, most notably non-trivial equilibrium states coming out of the insurgence of long-lived coherent structures, or unexpected response to conventional excitation and manipulation schemes. These properties may be used to the aim of an active control of the electron sample positioning and charge.