Pure electron plasmas in asymmetric traps*

Autoresonances of m=2 diocotron oscillations in non-neutral electron plasmas

The existence of autoresonances for m=2 diocotron oscillations of non-neutral electron plasmas in a uniform magnetic field was predicted by particle-in-cell simulations and it was confirmed in experiments. The obtained results show clear deviations from the standard threshold amplitude dependence on the sweep rate. The threshold amplitude approaches a constant at a lower sweep rate when there is a damping force. It was also found that the aspect ratio for the oval cross section of the confined plasma can be controlled by the frequency of the externally applied driving force.

Electron plasma orbits from competing diocotron drifts

The perpendicular dynamics of a pure electron plasma column are investigated when the plasma spans two Penning-Malmberg traps with noncoinciding axes. The plasma executes noncircular orbits described by competing image-charge electric-field (diocotron) drifts from the two traps. A simple model is presented that predicts a set of nested orbits in agreement with observed plasma trajectories.

Admissible equilibria of non-neutral plasmas in a Malmberg-Penning trap

A "parallel current constraint" is derived, that in combination with the Poisson equation allows one to select admissible equilibria of non-neutral plasmas in a Malmberg-Penning trap in the presence of a nonuniform and nonaxisymmetric magnetic field. Asymmetry-induced currents (analogous to the Pfirsch-Schlüter currents in Tokamaks) appearing in a non-neutral plasma even in the absence of magnetic drifts are explicitly computed in the case of a uniformly tilted magnetic field.

Second harmonic autoresonant control of the l=1 diocotron mode in pure-electron plasmas

An oscillator whose frequency is amplitude dependent can be controlled by a drive whose frequency sweeps through a resonance with the oscillator's fundamental frequency. This phenomenon is called autoresonance, and has been previously investigated for drives with frequencies near the oscillator's fundamental or subharmonic frequencies. This paper examines autoresonance for drives at twice the fundamental frequency, i.e, second harmonic autoresonance. The l=1 diocotron mode in pure-electron plasmas, a very high Q nonlinear oscillator, is the focus of the paper. The theory for this oscillator is derived, and compared to experimental results. The results can be generalized to any Duffing-like driven nonlinear oscillator in which the coupling between the drive and the oscillator depends at least weakly on the oscillator amplitude.