Direct experimental observation of π-mode oscillation in arelativistic magnetron

The authors report the direct measurement of the operating mode of a relativistic magnetron. The S-band 2.65-GHz magnetron used has a washer cathode and is driven by a 1-MV 2.8-Ω 65-ns pulser. Power and pulse shape are measured simultaneously by calibrated couplers, cables, and crystal diodes. The frequency is measured as the heterodyne or difference frequency between a local oscillator and the extracted signal. This difference frequency is several-hundred megahertz. By directly measuring the phase relationship, any questions concerning perturbations of the resonance by the large current of relativistic electrons are avoided