Nondestructive Gyrotron Cold-Cavity Q Measurements

A novel method for cold testing a gyrotron resonator to determine its total Q is presented. Probing radiation is coupled into the resonator through its radiation pattern. A sensitive heterodyne receiver is used in the far field to detect the reradiated cavity resonances. Good agreement between measurement and calculated total Q is found for several 140-GHz gyrotron resonators in the TE/sub 031, TE/sub 032/, TE/sub 231/, and TE/sub 611/ modes.