NEW METHOD OF MEASURING THE NOISE PARAMETERS OF THE ELECTRON BEAM, ESPECIALLY THE CORRELATION BETWEEN ITS VELOCITY AND CURRENT FLUCTUATIONS

摘要

The noise figure of a microwave beam amplifier has a lower limit that depends entirely upon the noise process in the electron gun at and near the potential minimum. This report is chiefly concerned with the theory and experimental results of a new method of measuring the noise parameters of the electron beam, especially the cor¬relation between its velocity and current fluctuations, by using a selective beam coupler that has properties similar to the conventional microwave directional cou¬pler. The value of the correlation coefficient of the velocity and current fluctuations was found to be from 0.2 to 0,35 in the space-charge-limited region and zero, or slightly negative, in the temperature-limited region. The probable error of this meas¬uring method is discussed by taking account of the residual selectivity of the selective beam coupler, the effect of the pickup cavities upon the beam, the thermal noise from these cavities, and the higher-order modes.