Experimental investigation of the ion resonance instability in a trapped electron plasma

Abstract

An investigation of the ions induced diocotron instability in an electron plasma confined in a Malmberg-Penning trap is presented. The detection of the instability is based on the spectral analysis of the induced charge signals on the walls of the confining electrodes, which allows tracking of the plasma displacement from the axis. The dependence of the instability on the electron energy is analysed by three different methods: (i) injecting electrons with different energies, (ii) heating the electrons with a single radio frequency burst, (iii) varying the ramp-up time of the confining voltage. An experimental technique to limit the ion resonance instability, based on the application of suitable potentials on a set of electrodes, is presented.

Stabilizing effect of a nonresonant radio frequency drive on the m=1 diocotron instability

“…7. In brief, under the assumption that the radius of the plasma column is much smaller than the trap radius R W , the column is approximated with a rigid rod of linear charge density P and length L P .…”

“…Contrary to the algebraic instability predicted by the linear theory, 3,4 experiments have shown an exponential growth of the plasma displacement, 5 leading to a progressive loss of particles on the electrodes' surface. The instability can be triggered by several reasons, e.g., presence of ions, 6,7 application of an oscillating dipole excitation in resonance with 1 on a twofold split electrode, and application of a resistive load on a sector of a split electrode. 8,9 Several mechanisms exist that lead to a damping of the m = 1 diocotron mode.…”

Ion-Induced Instability of Diocotron Modes in Electron Plasmas Modelling Curvature-Driven Flute Modes

“…Instabilities of diocotron modes are commonly observed when small ion fractions are added to pure electron plasmas [10][11][12][13][14][15][16] . However, historically 10 these instabilities were first thought to be driven by the difference in rotation frequencies of the two species caused by inertial (mass difference) effects.…”

Diocotron instability in non-neutral plasmas with a stationary point in the rotation frequency profile

“…More recently, a numerical treatment of this case was presented in Refs. 30,31 The analysis in the following is restricted to the case where l = 1. The simulations predict an exponential growth of the instability but with a growth rate that is still by more than a factor of 2 less than that deduced from the experimental data.…”