A pulsed power approach to pumping dielectric-filled rf cavities

Summary form only given, as follows. Acceleration of high current pulses within the framework of conventional charged-particle accelerator architectures. The key to the concept is that high dielectric-constant materials can store much greater electromagnetic energy than a similar size vacuum cavity. For water, with e/eo=80, this additional energy storage can result in proportionately higher particle currents before cavity depletion. Alternately, relatively low frequency operation is possible in modest sized cavities, since the resonant frequencies scale as (eo/e)1/2. In either case, the high dissipation rate of water leads to design constraints. The Q of the cavity is intrinsically low, independent of wall material. This has the advantage that low quality wall finishes are potentially feasible, and also that the filling time can be modestly short. It has the disadvantage that high gradient fields will dissipate significant energy in the cavity material. This probably restricts dielectric-filled cavities to pulsed accelerator systems. A more serious problem is that high power sources are required to reach fields of a few MV/m strength. A possible solution for this is to employ wakefield techniques to pump the cavities. This procedure uses the inductive fields on the rising current segment of an intense electron beam to power the resonant dielectric cavities. Also known as autoacceleration, this concept has been discussed for almost thirty years. With the advent of multi-kiloampere, multi-microsecond long electron beam technology, this concept becomes an attractive method for exploiting the advantages of dielectric-filled resonant cavities. Analysis and simulations of wakefield pumping of such cavities will be presented.