Collisionless Shock Driven by a Supersonic Velocity Shear

Abstract

The long-term evolution of a relativistic collisionless velocity shear in an unmagnetized electron-positron plasma is investigated using a first-principle particle-in-cell simulation. The Alves instability converts the shear kinetic energy into thermal and magnetic field energy. The resulting pressures push the plasma, leading to the formation of collisionless shocks. The generated collisionless shocks would accelerate high energy particles, which is a possible solution to the injection problem of shear acceleration. In addition, the collisionless shocks generate a magnetic field turbulence that is required for the shear acceleration to work.