Electron acceleration by wave turbulence in a magnetized plasma

Astrophysical shocks are commonly revealed by the non-thermal emission of energetic electrons accelerated in situ ^1-3 . Strong shocks are expected to accelerate particles to very high energies ^4-6 ; however, they require a source of particles with velocities fast enough to permit multiple shock crossings. While the resulting diffusive shock acceleration ⁴ process can account for observations, the kinetic physics regulating the continuous injection of non-thermal particles is not well understood. Indeed, this injection problem is particularly acute for electrons, which rely on high-frequency plasma fluctuations to raise them above the thermal pool ^7,8 . Here we show, using laboratory laser-produced shock experiments, that, in the presence of a strong magnetic field, significant electron pre-heating is achieved. We demonstrate that the key mechanism in producing these energetic electrons is through the generation of lower-hybrid turbulence via shock-reflected ions. Our experimental results are analogous to many astrophysical systems, including the interaction of a comet with the solar wind ⁹ , a setting where electron acceleration via lower-hybrid waves is possible.