Acceleration of solar wind ions to 1 MeV by electromagnetic structures upstream of the Earth's bow shock

TL;DR

This paper reports in situ measurements showing electromagnetic structures can rapidly accelerate ions to 1 MeV outside Earth's bow shock, revealing a universal mechanism for ion heating in space plasmas.

Contribution

It demonstrates a novel stochastic acceleration mechanism involving electromagnetic structures causing ion gyro-phase breaking and chaos, applicable across various astrophysical environments.

Findings

Ions are accelerated to 1 MeV outside the bow shock.

Electromagnetic structures induce stochastic perpendicular ion acceleration.

This mechanism may be universal in space plasma heating.

Abstract

We present measurements from the ESA/NASA Cluster mission that show in situ acceleration of ions to energies of 1 MeV outside the bow shock. The observed heating can be associated with the presence of electromagnetic structures with strong spatial gradients of the electric field that lead to ion gyro-phase breaking and to the onset of chaos in ion trajectories. It results in rapid, stochastic acceleration of ions in the direction perpendicular to the ambient magnetic field. The electric potential of the structures can be compared to a field of moguls on a ski slope, capable of accelerating and ejecting the fast running skiers out of piste. This mechanism may represent the universal mechanism for perpendicular acceleration and heating of ions in the magnetosphere, the solar corona and in astrophysical plasmas. This is also a basic mechanism that can limit steepening of nonlinear electromagnetic structures at shocks and foreshocks in collisionless plasmas.