Compression Acceleration of Protons and Heavier Ions at the Heliospheric Current Sheet

TL;DR

This study models how magnetic reconnection at the heliospheric current sheet accelerates protons and heavier ions, producing nonthermal energy distributions consistent with Parker Solar Probe observations, and explores how ion energy cutoffs depend on charge-to-mass ratios.

Contribution

It introduces a transport equation approach to simulate multi-ion acceleration at the HCS, revealing the spectral properties and charge-to-mass scaling of energetic ions.

Findings

Ion spectra follow power-law distributions matching observations.

Proton energy cutoff can reach up to 1 MeV depending on diffusion.

The charge-to-mass ratio influences the maximum ion energy with a specific scaling law.

Abstract

Recent observations by Parker Solar Probe (PSP) suggest that protons and heavier ions are accelerated to high energies by magnetic reconnection at the heliospheric current sheet (HCS). By solving the energetic particle transport equation in large-scale MHD simulations, we study the compression acceleration of protons and heavier ions in the reconnecting HCS. We find that the acceleration of multi-species ions results in nonthermal power-law distributions with spectral index consistent with the PSP observations. Our study shows that the high-energy cutoff of protons can reach $E_{max} \sim 0.1$ - $1$ MeV depending on the particle diffusion coefficients. We also study how the high-energy cutoff of different ion species scales with the charge-to-mass ratio $E_{max} \propto (Q/M)^\alpha$. When determining the diffusion coefficients from the quasilinear theory with a Kolmogorov magnetic power spectrum, we find that $\alpha \sim 0.4$, which is somewhat smaller than $\alpha \sim 0.7$ observed by PSP.