Dielectric-filled radiofrequency linacs

High current, high brightness electron beam accelerators promise to open up dramatic new applications. Linear induction accelerators are currently viewed as the appropriate technology for these applications. A concept by Humphries and Hwang may permit radiofrequency accelerators to fulfill the same functions with greater simplicity and enhanced flexibility. This concept involves the replacement of vacuum if cavities with dielectric filled ones. Simple analysis indicates that the resonant frequencies are reduced by a factor of (ε0 / ε)^½ while the stored energy is increased by ε / ε0. For a high dielectric constant like water (H2O), this factor, can approach 80. We have performed a series of numerical calculations of simple pill-box cavities. Eigenfunctions and resonant frequencies for a full system configuration, including dielectric material, vacuum beamline, and a ceramic window separating the two have been computed. These calculations are compared with the results of a small experimental cavity which we have constructed and operated. Low power tests show excellent agreement.