STIMULATED DIELECTRIC WAKE-FIELD ACCELERATOR

A wake-field accelerator is described based on the use of a waveguide structure in which many modes can participate in wake-field formation, and in which the wake-field period equals the period of a train of dr ive bunches. A dielectric-lined waveguide is analyzed that is shown to support multimode propagation with all modes having nearly equal phas e velocities, equal to the initial velocity of injected charge bunches that drive the wake fields. For this waveguide, the ratio of wake fie ld to drag field for a bare drive bunch is 4.7, as compared to 2.0 for a single-mode waveguide. The composite TM0n wake field of such a stru cture is shown to include highly peaked axial electric fields localize d on each driving bunch in a periodic sequence of bunches. This allows stimulated emission of wake-field energy to occur at a rate that is l arger than the coherent spontaneous emission from a single driving bun ch of equal charge and energy. This mechanism can make possible the de sign of a stimulated dielectric wake-field accelerator that,has the po tential of providing an acceleration gradient for electrons or positro ns in the range of 50-100 MV/m, taking a driving bunch charge of a few nC. We present calculations for such wake fields from a bunched sheet beam in a two-dimensional dielectric waveguide. Numerical examples ar e given, including the acceleration of a 30 MeV test bunch to 155 MeV in a structure 200 cm in length, using ten identical 2 nC/mm drive bun ches.