Field amplification, vortex formation, and electron acceleration in a
  plasma protoshock: effect of asymmetric density profile
  Gamma ray bursts (GRBs) are thought to originate from highly relativistic
jets. The fireball model predicts internal shocks in the jets, causing magnetic
field to be amplified and particles to be accelerated. We model the effects of
an asymmetric density configuration for an internal plasma collision in a
quasi-parallel magnetic field. We measured electron acceleration and found that
a tenuous population of electrons is accelerated to Lorentz factors of \sim 300
- close to energy equipartition with ions. We found that the filaments did not
remain static, but were deflected by the Lorentz force and rolled up into small
vortices, which themselves merge to form a larger current vortex.
