Contributed Talk - Splinter SNR

Tuesday, 12 September 2023, 16:00   (H 2035)

The mechanism of efficient electron acceleration at parallel non-relativistic electron-ion shocks

Mohamad Shalaby
Leibniz Institute for Astrophysics Potsdam

Cosmic-ray-driven instabilities are crucial in particle acceleration at shocks and during the movement of cosmic rays in galaxies and galaxy clusters. These instabilities amplify magnetic fields, affecting cosmic ray transport and connecting the collisionless cosmic ray population with thermal plasma, offering significant dynamic feedback. The talk discusses a recent discovery of a CR-driven instability (referred to as intermediate-scale instability), which triggers comoving ion-cyclotron electromagnetic waves at sub-ion skin-depth scale and operates when the ratio of drift speed with respect to the ion Alfvénic speed is less than sqrt(mi/me)/2, where mi (me) is the ion (electron) mass. Its growth rate is notably faster compared to the ion gyro scale, playing a vital role in charged particle acceleration and transport in galactic and stellar settings. The talk explores implications of this instability and demonstrates through Particle-in-cell simulations that it's the sole mechanism for efficient electron acceleration at parallel electron-ion shocks, addressing a persistent electron-injection issue at these shocks. Consequently, the common practice of using reduced ion-to-electron mass ratios in plasma simulations (which artificially suppresses the intermediate instability) not only hinders electron acceleration but also leads to incorrect electron and ion heating in downstream and shock transition areas.