Pickup Ion Effect of the Solar Wind Interaction with the Local Interstellar Medium

TL;DR

This paper presents a 3D numerical simulation of the heliospheric interface treating pickup ions as a separate fluid, revealing their significant influence on plasma pressure and heliosheath structure.

Contribution

It introduces a novel model that separately treats pickup ions in 3D simulations, aligning with Voyager observations and improving understanding of heliospheric plasma dynamics.

Findings

Pickup ions carry most of the plasma pressure in the supersonic solar wind.

The model predicts a decrease in heliosheath width due to pickup ion effects.

Simulation results align with Voyager observations of energy transfer at the termination shock.

Abstract

Pickup ions are created when interstellar neutral atoms resonantly exchange charge with the solar wind (SW) ions, especially in the supersonic part of the wind, where they carry most of the plasma pressure. Here we present numerical simulation results of the 3D heliospheric interface treating pickup ions as a separate proton fluid. To satisfy the fundamental conservation laws, we solve the system of equations describing the flow of the mixture of electrons, thermal protons, and pickup ions. To find the density and pressure of pickup ions behind the termination shock, we employ simple boundary conditions that take into account the \emph{Voyager} observations that showed that the decrease in the kinetic energy of the mixture at the termination shock predominantly contributed to the increase in the pressure of pickup ions. We show that this model adequately describes the flow of the plasma mixture and results in a noticeable decrease in the heliosheath width.