Ion Temperature Anisotropy in Plasma Jets

Abstract

Magnetotail magnetic reconnection results in fast plasma flows referred to as jets. Reconnection jets are populated with complex non-Maxwellian ion distributions providing a source of free energy for the micro-instabilities, which contribute to the ion heating in the reconnection region. We present a statistical analysis of the ion temperature anisotropy in magnetic reconnection jets using data from the Magnetospheric Multiscale spacecraft. Compared with the quiet plasma in which the jet propagates, we often find anisotropic and non-Maxwellian ion distributions in the plasma jets. We observe magnetic field fluctuations associated with unstable ion distributions, but the wave amplitude is not large enough to scatter ions during the observed lifetime of the jet. Our estimate of the phase-space diffusion due to chaotic and quasi-adiabatic ion motion in the current sheet shows that the diffusion is sufficiently fast to be the main process leading to isotropization.