New plasma concepts for enhanced microwave vacuum electronics

Summary form only given. Recently, new concepts in the field of microwave radiation generation have led to the possibly of major advances on the frontier of microwave vacuum devices. These concepts include the emerging technology of DC to AC radiation converters, or DARC sources, ionization fronts for frequency upshifting and conversion of extremely large plasma wakes into a Cherenkov radiation source. In the DARC source, alternatively biased "capacitors" produce a static electric field, which upon passing through a moving relativistic, underdense ionization front, is converted into a short pulse of electromagnetic (EM) radiation. The frequency of this em wave is tunable by varying either the plasma density or the spacing between capacitors. We will discuss the technology involved in going from the proof of principle design which produced only a few tens of milliwatts of microwave power, to current devices at the 100 W range, to future devices at the kilowatt and megawatt levels of output power. In the planned Cherenkov source, a fraction of the energy stored in the large amplitude electrostatic wave (wake) generated in plasma based accelerators is converted into EM radiation by applying a static magnetic field perpendicularly to the driving laser beam. The laser beam couples to the L branch of the XO mode of the magnetized plasma through Cherenkov radiation. This radiation is emitted predominantly in the forward direction at the plasma frequency (THz range).