GV/m Wake Fields Generated by a Train of pC Femtosecond Bunches in a Planar Dielectric Microstructure

A tall, dielectric-lined rectangular wake field microstructure is analyzed as a possible element of an advanced linear wake field accelerator. This accelerator would be driven by a train of fs 500-MeV electron microbunches that would be chopped out of a longer bunch using e.g. a powerful CO2 laser, and then formed into a train of rectangular-profile bunches using a quadrupole. The bunches set up a periodic wake field in the microstructure, using a train of bunches spaced by the period of the wake fields in the structure. Stability is examined for drive and accelerated bunches using computations of test particle orbits in the longitudinal and transverse wake fields excited by the drive bunches. It is found that nearly all test electrons in the drive bunches are confined within the structure for a travel distance of 15 cm or more, while test electrons located in an accelerated bunch can have stable motion over the same distance in a gradient of 0.4 GV/m without passing through the structure walls. A single 25-pC bunch will set up gradients of 1.16 GV/m and will permit stable acceleration over a 10-cm distance with very low energy spread in the same structure