Collisionless shock interaction 1 Collisionless shocks 1 Electrostatic collisionless shock 1 Electrostatic shocks 1 Electrostatics 1 Head-on collision 1 Magnetic fields 1 Particle-in-cell simulations 1 Plasma simulation 1 Shock interactions 1 Shock waves 1 Strong magnetic fields 1 Weibel instability 1 collisionless shock interaction electrostatic collisionless shocks 1 particle-in-cell simulations 1