RF design of a compact, X-band travelling-wave RF photogun made from halves

This paper presents the RF design, thermal calculations and beam dynamics simulations of a compact, high repetition rate, travelling-wave RF photogun operating at the European X-band frequency of 11.994 GHz. The design is based on a CLIC prototype structure milled from copper halves and proposes to use the unique gap, introduced in the original X-band accelerating structure's geometry, to couple in the photocathode laser without obstructing the outgoing electron bunches. Operating at an input RF power of 29 MW and combined with a single X-band structure downstream, the non-cylindrically symmetric travelling-wave RF photogun operates as a compact photo-injector able to provide 40 pC bunches with an energy of 34.4 MeV +/- 0.07 %, a bunch length of 533 fs and a horizontal and vertical emittance of 0.368 and 0.338 mm mrad, respectively, at a repetition rate up to 1 kHz.