Dielectric Wake Field Resonator Accelerator Module

60975 The wake field induced by passage of a high charge bunch along a dielectric-lined wavequide is attractive for high-gradient electron acceleration, such as used in high energy physics research, since 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. However, a long dielectric-lined waveguide, is required for a long bunch train, leaves the bunches susceptible to serious instability. This project will develop a short dielectric resonator that would allow cumulative buildup of the wake fields, if the wake field reflections from both resonator faces could be synchronized with the period of the bunch train. A short dielectric resonator could allow easier control of transverse beam instabilities than a long dielectric waveguide. In Phase I, transverse instability was investigated for a bunch injected slightly off-axis in a dielectric-line waveguide, and a fair degree of stabilization was exhibited. A simulation of longitudinal wake fields in a dielectric resonator exhibited zones adjacent to each face of the resonator where the wake fields did not resemble those calculated, unless axial boundaries were taken into account. An experimental dielectric wake field resonator was designed and built, and a design for a beamline upgrade was developed, so as to increase the charge/bunch for future experiments. Phase II will upgrade the beamline, including the installation of an alpha magnet to provide higher charge, tighter bunches, along with improved beam focusing into the dielectric resonator. A beam chopper will be constructed to enable an adjustable short train of bunches to pass into the dielectric resonator. Experiments will be performed to observe the cumulative build-up of wake fields from the bunch train. Commercial Applications and Other Benefits as described by the 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. Significant acceleration in a dielectric resonator could open up sizable markets for future accelerator modules.