Generation, dynamics and coherent structures in RF-generated trapped non-neutral plasmas

In magnetized non-neutral plasmas, features like turbulence and self-organization are observed as a consequence of the Kelvin-Helmholtz instability. With respect to the case of a quiescent single-species distribution and axisymmetric, static boundary conditions, the presence of multiple species and/or the application of radio-frequency (RF) electric perturbations (conditions that may be either unwanted or intentionally pursued) can significantly affect the plasma dynamics and equilibrium. This is the case when the plasma is generated via residual-gas ionization by an external forcing: The interplay of phenomena occurring over different time scales leads to a much more complicated evolution, characterized by the formation of coherent structures and non-axisymmetric final states showing unexpected robustness properties against usual instabilities. The paper discusses the formation of electron vortices reaching an off-axis equilibrium under the continuous application of the RF drive and, through both indirect and direct measurement, shows that a significant fraction of positive ions can be simultaneously confined together with the electron plasma.