Relativistic magnetrons and klystrons at long pulse durations

Extending the pulse duration of high power, relativistic microwave sources beyond ≈100 ns is a great challenge because of pulse shortening mechanisms such as gap closure and RF breakdown. We are exploring the long pulse operation of both relativistic magnetrons and relativistic klystron amplifiers. Together they represent the major classes of HPM sources: crossed field devices and linear beam tubes. We are improving the quality of the surface conditions by a variety of techniques, operating at low (∼10⁻⁷Torr) vacuum and reducing the electric fields in the interaction region where possible. Thus far we have produced high power magnetron pulses with durations of 400 ns and conducted a beam propagation experiment on the RKA which shows stable operation for the entire duration of the electrical pulse.