Design and construction of a chopper driven 11.4 GHz traveling wave RF generator

The authors discuss the design and construction features of a high-power RF generator comprising a 5.7-GHz chopping system and 11.4-GHz high group velocity, traveling-wave structures. The device is designed for operation with high current megavoltage beams and has been developed in support of the Relativistic Klystron High Gradient Accelerator program. The RF chopping system operates under immersed beam conditions with an axial magnetic field matched to the beam emittance and betatron resonance requirements so that the 11.4-GHz RF current is maximized. The TW circuit shunt impedance was chosen to enable high levels of beam-induced RF power to be generated without exceeding safe E-field values. The use of high group velocity structures having a short interaction region enabled an RF filling time of only 1050 ps to be achieved, thereby providing a broadband, phase- and temperature-insensitive circuit having fast response characteristics consistent with the intended 1000-A 40-ns beam pulse operation