Mirror instability driven by pickup ions in the outer heliosheath

Abstract

<p><span class="fontstyle0">Kinetic linear instability analysis and hybrid simulations are carried out to examine the role of mirror instability in scattering the pickup ions in the outer heliosheath. The dynamics of these pickup ions is essential to<br />the understanding of the energetic neutral atom (ENA) ribbon observed by the Interstellar Boundary EXplorer<br />(IBEX). While most previous studies have focused on the ion cyclotron instability driven by the pickup ions,<br />recent work based on a simple ring velocity distribution of the pickup ions suggested that the mirror mode can<br />also be unstable and contribute to the scattering of the pickup ions. The present study performs linear analysis<br />as well as hybrid simulations for a more realistic, multi-component pickup ion velocity distribution given by the<br />global modeling of neutral atoms in the heliosphere. The linear theory results indicate unstable mirror modes<br />with considerable growth rates. The corresponding hybrid simulations further confirm that the mirror modes can<br />grow and aid the pitch-angle broadening of the pickup ions. So the role of mirror mode should not be ignored in<br />the stability study of the outer heliosheath pickup ions.</span> </p>