Development of an Ultra-Bright Electron Source for Scanning Transmission Electron Microscopy

65078 The wake field induced by passing a high charge bunch along a dielectric-lined waveguide is attractive for high gradient electron acceleration, because no external source of radiation is needed. Recently, it was pointed out that a train of short moderate charge bunches can be arranged to induce cumulative buildup of wake fields, when the bunch period equals the wake field period. However, a long dielectric waveguide ¿ required for a long bunch train ¿ leaves the bunches susceptible to serious instability. This project will develop a short dielectric resonator that allows the cumulative buildup of wake fields, since wake field reflections from both resonator faces can be synchronized with the period of the bunch train. The control of instabilities should be easier for a short dielectric resonator than a long dielectric waveguide. In Phase I, the theory for wake fields in dielectric resonators will be refined in order to optimize the resonator design and to study instability. Experiments to observe buildup in wake field amplitude in a dielectric resonator will be conducted, using a train of bunches created by an available S-band rf gun and associated beamline. Commercial Applications And Other Benefits as described by awardee: High-gradient wake fields, induced by the passage of a train of moderate charge bunches, could be an alternative to large, expensive, rf-driven systems for acceleration of electrons and positrons to high energy. If significant acceleration in a dielectric resonator can be demonstrated, a sizable market should open up for future accelerator modules.