A chopper system for the MAX IV thermionic pre-injector

The MAX IV pre-injector will have one thermionic and one photocathode S-band RF gun, where the former will be used for ring injections. During ring injections, the bunches leaving the pre-injector have a structure that consists of ten 10 ns bunch trains, each containing three bunches. A chopper system consisting of two striplines and an adjustable aperture is used, where the desired bunch structure is obtained by superposing RF signals. The design of the chopper system and the initial tests of the thermionic pre-injector are presented in this paper.