High Energy Particle Acceleration by Shock Surfing

*Masahiro Hoshino[1] ,Nobue Shimada [1]
University of Tokyo[1]

It is believed that the supra-thermal particle acceleration as well as the plasma thermalization occurs in the neighborhood of collisionless shock front regions through the interaction of particles with the electrostatic and electromagnetic waves excited by a wide variety of plasma instabilities. In this talk, supra-thermal particle acceleration for a perpendicular magnetosonic shock is discussed by focusing on the interaction of particles with a large amplitude solitary wave formed in the shock front region/shock transition layer. The shock front region was thought to be highly turbulent, but in addition to such a turbulence, a series of large-amplitude, small-scale solitary waves embedded in the shock transition layer are observed by the modern satellites' observations in the earth's bow shock. Motivated by the discovery of the small-scale solitary waves, we study their effect on the particle acceleration by using the particle-in-cell simulations. We find that the electrostatic solitary waves are excited in the ion-electron shocks by a two-stream instability between the incoming electrons and the reflected ions from the shock front [Shimada and Hoshino, ApJ Lett 2001]. We discuss that the electrons trapped by the solitary wave can resonate with the shock motional electric field in the shock transition layer, and the so-called shock surfing mechanism is effective for producing the non-thermal, high-energy electrons. We show that the trapped electron can be accelerated up to the shock potential energy determined by a global shock size when the Alfven Mach number Ma exceeds about 10-100.