High-brightness, symmetric electron bunch generation in a plasma wakefield accelerator via a radially-polarized plasma photocathode

The plasma photocathode has previously been proposed as a source of ultrahigh-brightness electron bunches within plasma accelerators. Here, the scheme is extended by using a radially-polarized ionizing laser pulse to generate high-charge, high-brightness electron bunches with transverse emittance. Efficient start-to-end modeling of the scheme, from ionization and trapping until drive bunch depletion, enables a multiobjective Bayesian optimization routine to be performed to understand the performance of the radially-polarized plasma photocathode, quantify the stability of the scheme, and explore the fundamental relation between the witness bunch charge and its emittance. Comparison of plasma photocathodes driven by radially- and linearly-polarized laser pulses shows that the former yields higher-brightness electron bunches when operating in the optimally-loaded regime.