Laboratory observation of ion acceleration via reflection off laser-produced magnetized collisionless shocks

TL;DR

This paper provides the first experimental evidence of ion acceleration via reflection off laser-produced magnetized collisionless shocks, supporting Fermi acceleration theories and revealing mechanisms relevant to space physics.

Contribution

It demonstrates direct experimental observation of ion energization from shock reflection in a controlled laboratory setting, advancing understanding of collisionless shock acceleration.

Findings

Observed quasi monoenergetic ion beams with 2-4 times shock velocity

Kinetic simulations confirmed ions were reflected and accelerated by the motional electric field

Results relate to ion acceleration mechanisms in Earth's bow shock

Abstract

Fermi acceleration by collisionless shocks is believed to be the primary mechanism to produce high energy charged particles in the Universe,where charged particles gain energy successively from multiple reflections off the shock front.Here,we present the first direct experimental evidence of ion energization from reflection off a supercritical quasi perpendicular collisionless shock,an essential component of Fermi acceleration in a laser produced magnetized plasma. We observed a quasi monoenergetic ion beam with 2,4 times the shock velocity in the upstream flow using time of flight method. Our related kinetic simulations reproduced the energy gain and showed that these ions were first reflected and then accelerated mainly by the motional electric field associated with the shock. This mechanism can also explain the quasi monoenergetic fast ion component observed in the Earth's bow shock.