[P-EM16] Space Plasma Physics: Theory and Simulation

[PEM16-P02] Self-generation of waves by energetic electron streaming at collisionless shocks

*Takanobu Amano¹ (1.Department of Earth and Planetary Science, University of Tokyo)

Keywords:shock wave, plasma, particle acceleration

The shock acceleration of charged particles in space has been a subject of extensive research over the decades. In particular, there has been remarkable progress recently in theory, in-situ observations, and kinetic simulations on the issue of electron injection into the standard diffusive shock acceleration (DSA). We have proposed stochastic shock drift acceleration (SSDA) as a mechanism of low-energy electron acceleration that has been demonstrated as a plausible model for electron injection. The common assumption both in DSA and SSDA is that the accelerated particles are efficiently scattered by waves around the shock. The scattering of low-energy electrons via resonant wave-particle interaction naturally requires relatively high-frequency and short-wavelength fluctuations, which are likely on the whistler-mode wave branch. It is clear that we need to understand the wave generation mechanisms and the resulting electron scattering efficiency for more quantitative theoretical modeling of nonthermal electron acceleration at shocks.

This study discusses the self-generation mechanisms of waves by sub-relativistic electrons being accelerated by an oblique collisionless shock. In particular, we focus on the generation of quasi-parallel high-frequency whistler waves as well as oblique low-frequency whistler waves. The former may be generated via the normal cyclotron resonance of relatively lower energy electrons, while the latter may result from the anomalous cyclotron resonance of higher energy electrons. The result of linear theory will be discussed and compared with published in-situ observations and kinetic simulation results.