Alternative shapes and shaping techniques for enhanced transformer ratios in beam driven techniques

The transformer ratio of collinear beam-driven acceleration techniques can be significantly improved by shaping the current profile of the drive bunch. To date, several current shapes have been proposed to increase the transformer ratio and produce quasi-uniform energy loss within the drive bunch. Some of these tailoring techniques are possible as a result of recent beam-dynamics advances, e.g., transverse-to-longitudinal emittance exchanger. In this paper, we propose an alternative class of longitudinal shapes that enable high transformer ratio and uniform energy loss across the drive bunch. We also suggest a simple method based on photocathode-laser shaping and passive shaping in wakefield structure to realize a shape close to the theoretically optimized current profiles.