Magnetic Reflection of Heavy Ions from High Mach Number Quasi-Perpendicular Shocks: MMS Observations

Strong shocks in collisionless plasmas, such as supernovae shocks and shocks driven by coronal mass ejections, are known to be a primary source of energetic particles. In this talk, I will discuss recent observations of nonstationarity and ion acceleration processes at high Mach number quasi-perpendicular shocks. Results are based on in-situ measurements of the Magnetospheric Multiscale (MMS) spacecraft at Earth's bow shock which in rare instances has shock parameters close to those predicted at supernova remnants. High time resolution and multipoint measurements enable us to characterize ion and electron scale kinetic effects and to distinguish spatial variations from time-dependent effects in the shock layer and upstream perturbations.

The shock dynamics are mostly driven by reflected ions, perturbations that they generate, and nonlinear amplification of the perturbations. These perturbations can transform into proto-shocks that propagate at small angles to the background magnetic field. Possible roles of ion-Weibel and Whistler instabilities are also discussed. The intense magnetic amplification at the shock front associated with nonstationarity modulates the trajectory of heavy ions, which then experience further acceleration in the upstream region. These results highlight the important role of high magnetic amplification in seeding heavy ions into the energization processes at nonstationary reforming shocks.