Intrinsic noise measurements in gyroklystrons

Summary form only given. Measurements of intrinsic shot noise in a 35 GHz, three-cavity gyroklystron have been obtained over a wide range of operating parameters. The noise emissions from both the input and output cavities were measured under carrier-free (zero-drive power) conditions. The spectrum of noise emitted by the input cavity is found to have a Lorentzian shape, with the peak frequency and spectral width in good agreement with the beam loaded frequency and Q predicted by simulation codes. At the nominal operating parameters of the gyroklystron, which were 70 kV, 10 A, /spl alpha/=1.27, and a magnetic field of 13.07 kG, we find the peak temperature of the input cavity noise to be 4.4/spl times/10/sup 8/ K (6.3/spl times/10/sup -15/ W/Hz), with a FWHM of 160 MHz. The peak noise temperature was found to exhibit complex variations with respect to beam current, beam velocity ratio, and magnetic field.