Slow-wave chopper structures for next generation high power proton drivers

A description is given of slow-wave chopper structures for the 3.0 MeV, 60 mA, H^- MEBT lines of the CERN Linac 4 and RAL Front-End Test Stand (FETS). Transmission line properties and transverse E-field uniformities for the original European spallation source (ESS) designs [1] have been refined by modelling electromagnetic fields in a commercial 3D finite difference time domain (FDTD) code [2]. In addition, the original compact, radiation hard, vacuum compatible designs have been simplified and reconfigured to be compatible with standard NC machining practice. Transmission line properties in the frequency and time domain, together with E-field uniformity in the axial and transverse planes, are presented.