Energy Conversion between Ions and Electrons through Ion Cyclotron Waves and Embedded Ion-scale Rotational Discontinuity in Collisionless Space Plasmas

Wave–particle interaction is a fundamental process in collisionless plasma, which results in the redistribution of energy between plasma waves and particle species. The analysis of high-resolution Magnetospheric Multiscale plasma and magnetic field data directly reveals the energy exchange between electromagnetic energy, particle bulk kinetic energy, and thermal kinetic energy in magnetosheath turbulence. This work focuses on the energy transfer associated with ion cyclotron waves (ICWs) and embedded rotational discontinuity (RD). We find that (1) the particle kinetic energy of ions is converted into electromagnetic energy; (2) the electrons are gaining energy from electromagnetic fields, having significant electron heating in the parallel direction around the RD; (3) the ICWs and RD connect and redistribute energy between ions and electrons in the post-shock downstream sheath region; and (4) the interactions between pressure tensor and strain tensor redistribute the ion and electron bulk and thermal kinetic energies, but less significantly than direct field–particle interaction by one order of magnitude in the ICW turbulence with weak compressibility.

 Work done by the electromagnetic field ions and electrons in 0.1–0.5 Hz. (a) and (b) The work done by the electromagnetic field on the ion species in the ion local and mean bulk flow reference frames, respectively. (c) and (d) The overall (i.e., time-integrated) work done by the electromagnetic field on the ion species in the ion local and mean bulk flow reference frames are illustrated, respectively. (e)–(h) The work and overall work done by the electromagnetic fields on the electrons in the electron local and mean bulk flow reference frames, respectively. The two black vertical dashed lines bound the interval of a rotational discontinuity (RD).

Flow chart of energy conversion related with kinetic-scale ICWs and the RD during the whole time interval (2017 October 7, 14:02:35–14:03:35) in 0.1–05 Hz. The bulk kinetic energy referred to the fluctuating bulk kinetic energy, the velocity of which has the mean bulk flow velocity subtracted.