Experiments on new plasma concepts for enhanced microwave vacuum electronics

Summary form only given. Recently new schemes have been proposed for plasma based microwave sources that could lead to output power increases by orders of magnitude, as well as offer new possibilities such as an broad band tuning and frequency chirping, ultra-short pulse generation, pulse design, etc. In the first scheme, the static field of an alternatively biased capacitor is directly converted into short pulses of tunable electromagnetic (em) radiation upon transmission through a relativistic, underdense ionization front. The structure presently under investigation consist of pin pairs (capacitors) inserted into an X-band waveguide through its narrow side wall and separated by 1.134 cm. In the second scheme, a fraction of the large amplitude electrostatic (es) wave generated in a plasma beat wave acceleration (PBWA) experiment (up to 3 GeV/m) is converted into em radiation by applying a static magnetic field perpendicularly to the driving laser beam. The two-frequency CO/sub 2/ laser beam resonantly drives the es wave, and couples to the L branch of the XO mode of the magnetized plasma through Cherenkov radiation. The radiation is emitted predominantly in the forward direction (direction of the laser beam), and is at the plasma frequency (n/sub e/=10/sup 16/ cm/sup -3/, f/spl ap/1 THz).