Mitigation of drift instabilities by a small radial flux of charged particles through the landau-resonant layer

Abstract

Experiments and theory on electron columns have characterized a novel algebraic damping of diocotron-like modes, caused by a small flux of halo particles through the resonant layer [1]. The damping rate is proportional to the flux. We have also investigated the diocotron instability which occurs when a small fraction of ions is transiting the electron plasma [2]. Dissimilar bounce-averaged E B drift dynamics of the ions and electrons polarizes the diocotron mode density perturbations, developing instability analogous to the classical flute instability. The exponential growth rate is proportional to the fractional neutralization and to the phase separation between electrons and ions in the wave perturbation. Here, we have shown that the flux-driven algebraic damping eliminates the ion-induced exponential instability of diocotron-like modes. Physically, the electric field from the resonant particles in the low-density halo acts back on the dense plasma core, causing E B drift motion of the core back down toward the trap axis, resulting in a damping of the mode.