L-Band Modulator for X-Band Linear Accelerator

The Air Force Research Laboratory requires a compact (<2m), high current, L-band modulator and buncher with broad bandwidth (>20% fractional bandwidth) capability. The modulator design should be optimized to provide L-band modulated electron beams of arbitrary waveform to a state-of-the-art X-band accelerator with peak beam current 75-250 mA, delivered over a 3 ?s macropulse with length of ~1m. It should provide consistent capture efficiency (>25%) going into the X-band accelerator across a variety of lower frequency (DC through L-band) modulated electron beams. This design should include a transition into X-band cavities such that it is integrable with an X-band accelerator. Also, the design must be scalable to higher frequency bands (S-band and beyond to W-band), be integrated with the X-band accelerator. RadiaBeam Technologies will develop an injector section, consisting of a buncher and a wideband L-band (1.14 ±10% GHz) modulator, based on the novel concept of twisted accelerating waveguide, which meets AFRL’s needs. In Phase I, the linac system will be designed the design will be verified with extensive simulations and fabrication studies. In particular, we will perform bunching section layout modelling and beam dynamics simulations to evaluate the requirements for each component. Based on the findings in the previous task, perform the RF design of the twisted waveguide section to satisfy the requirements for the phase velocity, field amplitude and bandwidth. Then start-to-end beam dynamics simulations will be performed to demonstrate the objective parameters. Fabrication studies of the twisted waveguide will be done by fabricating a short section, measuring its RF parameters and comparing with the modelling results. Finally, we will identify all sub-components and costs of the full prototype and develop plan for full system fabrication and testing in Phase II.