Hybrid simulations of the expanding solar wind: Temperatures and drift velocities

Abstract

We study the evolution of the expanding solar wind using a one‐dimensional and a two‐dimensional expanding box model [Grappin et al., 1993] implemented here within a hybrid code [Liewer et al., 2001]. We first consider a plasma with protons and 5% of alpha particles, without drift between the protons and alphas, considering successively the low‐beta and high‐beta cases. Then we consider a strong drift between protons and alphas, again separately the low‐beta and high‐beta case. Without drift, the evolution of the low‐beta plasma is adiabatic. In the high‐beta plasma without drift, the fire hose instabilities (both parallel and oblique) disrupt the adiabatic evolution. Finally, with a drift, the adiabatic evolution is stopped by the oblique Alfvén instability and the parallel magnetosonic instability for low‐beta plasma and for high‐beta plasma, respectively. The two instabilities slow down thealphas and heat alphas and protons.