UCLA

The energization of ions in a dynamic system containing two colliding magnetic flux ropes is investigated in an experimental study presented in this dissertation. Two kink-unstable flux ropes on the Large Plasma Device (LAPD) are made to collide in order to trigger magnetic reconnection, a process in which magnetic energy stored in the fields is dissipated into thermal and kinetic energy that is picked up by surrounding ions. The local energy distribution of the ions is measured by a four-grid ion retarding field energy analyzer that was constructed specifically for this study. The average energy ⟨2E⟩, a quantity equivalent to the Maxwellian temperature for non-Maxwellian distribution functions, was plotted as a function of time for two different flux rope conditions. In both cases, ⟨2E⟩ spikes indicated the presence of an ion beam with a sub-Alfv�nic drift velocity of 9 to 15�eV. The beam does not appear to be heated and the ion temperature of the ropes is estimated to be between 4 to 6�eV. This is found to be consistent with a spectrometer’s line-of-sight, volume-averaged measurement involving Doppler broadening of the 320.3�nm He�II spectral line. Using polar plots as a visualization tool for the two-dimensional ion distribution function, the beam appears to travel primarily in the +z direction along the magnetic field and out of the reconnection plane. The presence of the beam is also correlated with magnetic reconnection events that were identified by plotting line contour planes of the magnetic vector potential A_(z). This means that the ions are likely to be accelerated by -dA_(z)/dt, the inductive electric fields created during magnetic reconnection. Furthermore, the energy density produced by the induced electric fields (0.5�J/m�) is comparable to the energy per unit volume required to heat the ions from 6 to 10�eV (0.3�J/m�) after accounting for a less than 50% efficiency of energy transferred to the ions. Overall, the evidence presented in this study strongly suggests that the ions in the beam are produced by magnetic reconnection. To the author’s knowledge, this is the first experimental observation of a field-aligned ion beam generated in a reconnection experiment.