Electron acceleration by wave turbulence in a magnetized plasma

Rigby, A. and Cruz, F. and Albertazzi, B. and Bamford, R. and Bell, A. R. and Cross, J. E. and Fraschetti, F. and Graham, P. and Hara, Y. and Kozlowski, P. M. and Kuramitsu, Y. and Lamb, D. Q. and Lebedev, S. and Marques, J. R. and Miniati, F. and Morita, T. and Oliver, M. and Reville, B. and Sakawa, Y. and Sarkar, S. and Spindloe, C. and Trines, R. and Tzeferacos, P. and Silva, L. O. and Bingham, R. and Koenig, M. and Gregori, G. (2018) Electron acceleration by wave turbulence in a magnetized plasma. Nature Physics, 14. 475–479. ISSN 1745-2473 (https://doi.org/10.1038/s41567-018-0059-2)

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Astrophysical shocks are commonly revealed by the non-thermal emission of energetic electrons accelerated in situ1–3. Strong shocks are expected to accelerate particles to very high energies4–6; however, they require a source of particles with velocities fast enough to permit multiple shock crossings. While the resulting diffusive shock acceleration4 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 pool7,8. 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 wind9, a setting where electron acceleration via lower-hybrid waves is possible.