Toward a brightness upgrade to the SwissFEL: A high gradient traveling-wave rf photogun oleh Thomas Geoffrey Lucas, Hans-Heinrich Braun, Paolo Craievich, Reto Fortunati, Natalia Kirchgeorg, Anastasiya Magazinik, Marco Pedrozzi, Jean-Yves Raguin, Sven Reiche, Mattia Schaer, Mike Seidel, Riccardo Zennaro, David Alesini, Anna Giribono