RF-Diagnosis of magnetron-gun-injected hollow beams

In experiments with high perveance hollow beam klystrons a reproducible dependence of bunching efficiencies on the magnitude of the focusing field was found and reported earlier. Evaluation of small signal data, such as electronic gap loading and transadmittance, also reveal a dependence of these quantities on the focusing field. Known theories of RF-beam performance in finite magnetic fields do not explain the observed effects. No correlation between beam-interception and field dependence of RF-quantities was found. It is suggested that the observed phenomena are evidence of non-equilibrium beam conditions, in which part of the total kinetic energy of electrons is in transverse cyclotron motion. In devices using predominantly longitudinal interaction and bunching, a reduction of axial beam velocity is observable by its effect on measurable RF quantities. Data of the electronic gap loading over a wide range of applied voltage, perveance and magnetic field have been compared with ballistic calculations. An empirical relationship between the operating parameters of the beam and the energy in excess transverse motion could be established. The result is quantitatively applied to other groups of data, such as small signal trans-admittance and large signal bunching efficiencies. The agreement with calculated small and large signal performances at the reduced effective beam velocities supports this interpretation of the observed effects. Practical implications of the results of this investigation for the design of tubes using magnetron-gun-injected beams and some possible conclusions about the nature of the space charge flow will be discussed in this paper.