Nonthermal Particle Acceleration in Shock Front Region : "Shock Surfing Accelerations"

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概要

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• 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 paper, 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 tvrbulent, but in addition to such a turbulence, a series of large-amplitude, small-scale solitary waves embedded in the shock transition layer are obseved 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 study first a non-relativistic, high Mach number shock whose composition consists of ion and electron. 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. 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 M_A exceeds 10〜100. Next we investigate a relativistic shock whose plasma composition consists of electron and positron, i.e., pair plasma. We discuss that a magnetosonic solitary wave can take the place of the electrostatic solitary wave in the ion-electron shocks. As decreasing σ of the ratio of the upstream Poyinting flux to the upstream kinetic energy flux, the magnetosonic solitary wave forms the current sheet in the shock transition layer, which in turn can trap the paticles in the magnetic null region. We discuss that the shock surfing acceleration in a relativistic electron-positron shock occurs under the interaction of the trapped particles by the magnetosonic solitary wave with the shock motional electric field. The trapped particle can be efficiently accelerated up to the shock potential energy determined by a global shock size.

• 2000-10-26

著者

• Hoshino Masahiro

  Department Of Earth And Planetary Physics University Of Tokyo

• Hoshino Masahiro

  Department Of Applied Chemistry Waseda University

• Hoshino Masahiro

  Department of Earth and Planetary Physics, University of Tokyo

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• Nonthermal Particle Acceleration in Shock Front Region : "Shock Surfing Accelerations"

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