Diode plasma effects on the microwave pulse length from relativistic magnetrons

A model to account for the shortening of the relativistic magnetron microwave pulse length based on radial cathode plasma motion is put forth and corroborated with measurements. If the dense, conducting, cathode plasma (and not the cathode itself) sets the diode electrostatic and microwave boundary conditions, its motion changes the magnetron resonance condition. Time varying microwave power envelopes and frequencies are both expected and observed. Based on the cathode plasma expansion rate, the main plasma ton constituent is inferred to be hydrogen. A magnetron experiment to defeat the pulse-shortening mechanism by heating the resonator successfully lengthened the pulse from 100 to 115 ns.