Pickup Ion Acceleration at the Solar Wind Termination Shock Based on a Focused Transport Approach Including a q-Gaussian Turbulence Model of Variations in the Spiral Magnetic Field Angle

Abstract:

Voyager spacecraft observations indicate that interstellar pickup ions are accelerated to ~1 MeV locally at the solar wind termination shock. We present modeling results of the diffusive shock acceleration (DSA) of locally born interstellar pickup ions at the solar wind termination shock by solving the standard focused transport equation numerically. Local time variations in the Parker spiral magnetic field angle are modeled using a q-Gaussian statistical description. The main results are: (1) The injection and DSA of pickup ions depends on the shape and width of the q-Gaussian distribution of the Parker spiral magnetic field angle. (2) Likewise, the accelerated pickup ion pitch-angle distribution also depends on the q-Gaussian distribution of the magnetic field angle. (3) The simulated accelerated pickup ion spectrum is much quieter far downstream than just behind the termination shock as observations show. (4) Magnetic reflection of accelerated pickup ions by the cross-shock magnetic field gradient results in the sporadic formation of highly anisotropic, energy-dependent intensity spikes in the accelerated pickup proton distribution at the termination shock.