High Power High Frequency RF Generation

The principal goal of this project is to develop two RF power extraction structures (an X-band and a W-band device) to demonstrate high power high frequency RF generation using high current relativistic electron beams. High power high frequency RF sources have compelling applications in accelerators for high energy physics, communications, radar, etc. For high energy physics accelerator applications, klystrons are commercially available to provide a high quality RF power source below X-band frequencies. There are several facilities operating in the US at higher frequencies such as the X-band PPM klystron at SLAC [1], the X-band magnicon at NRL [2], the Ku band 17.1 GHz gyroklystron at University of Maryland [3], the 34 GHz Ka band magnicon at Yale/Omega-P [4], and the 94 GHz W band gyrotron [5]. In addition, many research programs are currently in progress that use different approaches to achieve high frequency output power and efficiency. However, stable, ultra-high power (e.g. multi-hundreds of MW in X-band and MW level in W-band as are proposed in this project) RF sources are still generally lacking for frequencies beyond X-band. Meanwhile, the portion of the spectrum with wavelengths from 3 cm to 3 mm is also very attractive due to the tight frequency availability in lower bands. Benefiting from the ~10 GW beam power provided by the high current linac at the Argonne Wakefield Accelerator (AWA) facility, we propose to develop a series of high power RF sources based on the extraction of coherent Cherenkov radiation from relativistic electron beams. The frequency spectrum of AWA beam (from the 1.3 GHz injector) covers up to W-band without the need for a complicated beam compression system. Simulations show that ~1 GW 20 ns RF pulses can be generated using an 11.7 GHz structure, ~400 MW for a 26 GHz structure, and ~14 MW for a 91 GHz structure [6]. The pulse length is expandable to 50 ns with a lower peak power.