Observation of Chaotic Particle Transport Driven by Drift-Resonant Fluctuations in the Collisionless Terrella Experiment.
This thesis presents the first observations of wave-induced collisionless radial transport in a laboratory terrella, the Collisionless Terrella Experiment (CTX). In the experiment an energetic population of trapped electrons is produced using electron cyclotron resonance heating (ECRH). The trapped electrons excite drift-resonant instabilities, identified as the hot electron interchange mode, during both the heating phase of the plasma discharge and in the afterglow, when the ECRH has been turned off. Electron transport is measured with a gridded particle detector and increases of electron flux to the detector are well correlated with the presence of the instability during the ECRH. The observed transport is strongly modulated at the precessional drift-frequency of the energetic electrons. No transport is observed at the detector during the afterglow. By integrating the equations of motion for a charged particle in a magnetic dipole field interacting with a spectrum of electrostatic waves we have established that the amplitude, frequency, and azimuthal mode number of the instabilities observed in both the ECRH phase and afterglow of the plasma discharge meet the conditions for the onset of chaotic particle motion. Numerical studies also show that the observed fluctuations drive chaotic radial motion which preserves the first two adiabatic invariants. Finally, by examining time-dependent Hamiltonian phase space flows, the modulation of the radial transport measured by the particle detector is shown to be the result of long-time correlations. The effect of long-time correlations is confirmed by a transport simulation which reproduces temporal features of the observed electron flux.
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- Physics: Fluid and Plasma