Particle energization in an expanding magnetized relativistic plasma

Using a 21 / 2-dimensional particle-in-cell (PIC) code to simulate the relativistic expansion of a magnetized collisionless plasma into a vacuum, we report a new mechanism in which the magnetic energy is efficiently converted into the directed kinetic energy of a small fraction of surface particles. We study this mechanism for both electron-positron and electron-ion (m(i)/m(e)=100, m(e) is the electron rest mass) plasmas. For the electron-positron case, the pairs can be accelerated to ultrarelativistic energies. For electron-ion plasmas, most of the energy gain goes to the ions.