Heating of Heavy Ions by Interplanetary Coronal Mass Ejection Driven Collisionless Shocks

Abstract

Shock heating and particle acceleration processes are some of the most fundamental physical phenomena of plasma physics, with countless applications in laboratory physics, space physics, and astrophysics. This study is motivated by previous observations of nonthermal heating of heavy ions in astrophysical shocks. Here we focus on shocks driven by interplanetary coronal mass ejections (ICMEs), which heat the solar wind and accelerate particles. This study focuses specifically on the heating of heavy ions caused by these shocks. Previous studies have focused only on the two dynamically dominant species, H + and He +2 . This study utilizes thermal properties measured by the Solar Wind Ion Composition Spectrometer (SWICS) aboard the Advanced Composition Explorer (ACE) spacecraft to examine heavy ion heating. This instrument provides data for many heavy ions not previously available for detailed study, such as oxygen (O +6 , O +7 ), carbon (C +5 , C +6 ), and iron (Fe +10 ). The ion heating is found to depend critically on the upstream plasma β, mass-to-charge ratio of the ion, M/Q, and shock magnetic angle, θ Bn . Ours is similar to past studies in that there is no strong dependence of ion heating on Mach number. The heating mechanism described in Lee & Wu is examined to explain the observed heating trends in the heavy ion thermal data. © 2007. The American Astronomical Society. All rights reserved.