Dynamics of a driver beam propagating in an underdense plasma with a downward density transition

When a short electron beam propagates in an underdense plasma (plasma density n/sub 0/ < beam density n/sub b/) with a downward density transition, it is known that some background plasma electrons are trapped and accelerated by the plasma wakefield. The beam quality of the trapped plasma electrons is severely affected by the wakefield that is generated by the driving electron beam, so dynamics and instabilities of the driver beam are very important. In this paper, we present some simulation results on the self-trapping and driver beam dynamics.