Wave-induced chaotic radial transport of energetic electrons in a laboratory terrella experiment

Abstract

This paper reports the observation of wave-induced chaotic radial transport of energetic electrons in a laboratory terrella, the Collisionless Terrella Experiment (CTX) [H. P. Warren and M. E. Mauel, Phys. Rev. Lett. 74, 1351 (1995)]. Electron cyclotron resonance heating is used to create a localized population of energetic electrons which excite the hot electron interchange instability. The electrostatic fluctuations driven by this instability have time-evolving spectra which resonate with the precessional drift motion of the hot electrons. We have established that the amplitude, frequency, and azimuthal mode number of the observed instabilities meet the conditions for the onset of chaotic particle motion. Electron transport is observed with a gridded particle detector. Increases in the flux of energetic particles to the detector are well correlated with the presence of fluctuations which meet the conditions for global chaos. Greatly diminished transport is observed when the fluctuations lead to thin, radially localized bands of chaos. The flux of energetic electrons to the detector is strongly modulated. By examining time-dependent Hamiltonian phase space flows, the modulation is shown to be the result of phase space correlations. A transport simulation based on the Hamiltonian motion of energetic electrons reproduces the frequency and modulation depth of the observed electron flux and allows for comparison between the Hamiltonian and quasilinear descriptions of transport.