Measurement of beam-loaded resonant frequency and quality factor in a gyroklystron input cavity using noise emissions

The spectral shape of noise emissions from a 35-GHz gyroklystron input cavity is used to directly measure the cavity resonant frequency and quality factor under beam-loaded conditions. The quality factors obtained with this technique at a number of magnetic fields are found to be consistent with quality factors obtained from reflection coefficient measurements made at the identical operating points. The measured variation in quality factor is used to identify various regimes of operation based on input cavity coupling. Comparisons between the measurements and simulations are in good agreement in resonant frequency, but moderate discrepancies in quality factor exist.