In situ evidence of ion acceleration between consecutive reconnection jet fronts

TL;DR

This study provides in situ evidence of ion acceleration between consecutive reconnection jet fronts in Earth's magnetotail, highlighting a Fermi-like acceleration mechanism that could be relevant in various astrophysical environments.

Contribution

It presents the first direct observation of ion acceleration between reconnection jet fronts and identifies a Fermi-like mechanism as the driver.

Findings

Ions are accelerated up to 150 keV between jet fronts.

Acceleration occurs mainly in the parallel direction, with ions trapped and energized.

The process is likely applicable to other astrophysical plasma environments.

Abstract

Processes driven by unsteady reconnection can efficiently accelerate particles in many astrophysical plasmas. An example are the reconnection jet fronts in an outflow region. We present evidence of suprathermal ion acceleration between two consecutive reconnection jet fronts observed by the Magnetospheric Multiscale mission in the terrestrial magnetotail. An earthward propagating jet is approached by a second faster jet. Between the jets, the thermal ions are mostly perpendicular to magnetic field, are trapped and are gradually accelerated in the parallel direction up to 150 keV. Observations suggest that ions are predominantly accelerated by a Fermi-like mechanism in the contracting magnetic bottle formed between the two jet fronts. The ion acceleration mechanism is presumably efficient in other environments where jet fronts produced by variable rates of reconnection are common and where the interaction of multiple jet fronts can also develop a turbulent environment, e.g. in stellar and solar eruptions.