# Chemical Enhancements in Shock-accelerated Particles: Ab-initio Simulations

## TL;DR

This study uses hybrid simulations to explore how ions with different mass and charge ratios are thermalized and accelerated in collisionless shocks, revealing mechanisms behind heavy-ion enhancements in cosmic rays.

## Contribution

It provides new insights into ion thermalization and acceleration processes, highlighting the role of ion charge and mass ratios in non-relativistic shocks.

## Key findings

- Ions thermalize to a temperature proportional to their mass number A.
- Non-thermal tails develop with extent scaling with Z and normalization with (A/Z)^2.
- Heavy ions are preferentially accelerated, explaining cosmic ray observations.

## Abstract

We study the thermalization, injection, and acceleration of ions with different mass/charge ratios, $A/Z$, in non-relativistic collisionless shocks via hybrid (kinetic ions-fluid electrons) simulations. In general, ions thermalize to a post-shock temperature proportional to $A$. When diffusive shock acceleration is efficient, ions develop a non-thermal tail whose extent scales with $Z$ and whose normalization is enhanced as $(A/Z)^2$, so that incompletely-ionized heavy ions are preferentially accelerated. We discuss how these findings can explain observed heavy-ion enhancements in Galactic cosmic rays.