Ramped bunch profile shaping using beam self-wakefields

Collinear wakefield accelerator approaches are limited to transformer ratios of less than two for symmetric drive profiles. Exceeding this limitation is necessary to establish dielectric wakefield acceleration as viable technology for future compact high-gradient accelerators. Novel methods are needed to generate asymmetric shaped drive beams ideal for enhanced transformer ratios. We propose to develop a longitudinal bunch shaper that is capable of generating nearly idealized triangular profiles using the beam self-wakefield interaction in a dielectric structure followed by a compact chicane. The shaped beam will serve as a driver for a second stage dielectric wakefield accelerator with enhanced transformer ratio. In Phase I, the system was conceptually designed and theoretically modeled with simulations for benchmarking. The system components were fabricated and assembled and installed for experimentation at the Brookhaven National Laboratory Accelerator Test Facility. The Phase I results experimentally demonstrated the generation of a beam with triangular profile consistent with theoretical modeling and simulations. In Phase II, we will build off the successful results and integrate a second stage structure to accelerate particles and measure the transformer ratio of the system. We will also explore alternate geometries and attempt higher-order shaping schemes. COMMERCIAL APPLICATIONS AND OTHER BENEFITS The benefits of dielectric wakefield accelerator structures include shaped bunches to extract energy, and access higher frequencies. It also provides high-added value in afterburner applications for existing facilities, allowing an increase in energy at negligible added footprint. The R&D has implications ranging from laser acceleration to high frequency components in communications. Finally, these structures serve as robust sources of terahertz radiation, (high peak power, narrow bandwidth) for material spectroscopy and pump-probe experiments.