Design considerations for a higher-order-mode dielectric-loaded power extractor set for millimeter-wave generation

The design of an electron-beam excited device for millimeter-wave generation is presented. Referred to as a dielectric-loaded power extractor, it is based on the higher-order-mode operation of a dielectric-loaded waveguide. With a matching transition, the unit can deliver power to the output waveguide at one of two frequencies, 20.8 and 35.1 GHz, corresponding to the TM02 and TM03 modes, respectively. By properly choosing the thickness of the dielectric lining, both modes are tuned to synchronize with an ultra-relativistic electron beam traversing the unit so that the wakefield generated by the beam is excited at these modes, chosen to be at 20.8 and 35.1 GHz, respectively, both corresponding to a harmonic of the 1.3 GHz operating frequency at an accelerator facility. Power generated in the unintended TM01 mode is effectively suppressed for bunch train operation by a novel technique. The device consists of a dielectric-loaded decelerating structure and two changeable output couplers to deliver the millimeter-wave power to a standard waveguide. For a drive beam with 50 nC of charge per bunch, power levels of 90.4 and 8.68 MW are expected to be delivered by the device at 20.8 and 35.1 GHz, respectively.