Calculation of Intra-Pulse Phase Shift in Linear Beam Microwave Tubes

摘要

The intra-pulse phase shift that occurs in a linear beam microwave tube, due to ion neutralization of the space charge of the electron beam, is calculated under certain simplifying assumptions. The final results, based on the well-known rate of ion formation in a gas, relates the phase change to the pulse length, gas pressure, beam voltage and current, and to the number of beam wavelengths in the interaction region. Using the theory derived herein, comparison of the calculated intra-pulse phase shift with that observed on operating tubes, indicates that this theory is accurate and that the ionization of residual gas, which results in an increase in the beam velocity, is the prime cause of intra-pulse phase shift. The mechanism whereby the phase shift is limited to a certain maximum value is discussed. It is shown that the phase requirements on the tube are ordinarily well within the value at which this limiting effect occurs, so a detailed treatment of the limiting mechanism would be of little interest to the tube designer. (Author)