Detailed measurements have been made of the dc and rf current distribution in a modulated, magnetically focused electron beam having normalized parameters in the range of values appropriate for practical medium‐power and high‐power klystrons. The ratio of the total rf current to the total dc current in the beam as a function of drift distance was determined experimentally under Brillouin‐flow conditions for selected values of α (the ratio of the rf voltage at the input gap to the dc beam voltage). These experimental values are compared with the results predicted theoretically. Similar experimental results are presented for higher focusing fields. Detailed radial distributions of the dc and rf current were experimentally determined by using an iris (a plate with a small hole) to allow only a small portion of the beam to be selected at any radial position. These measurements were made at various values of α and drift distance. The results for small values of α show, as predicted by theoretical considerations for a modulated Brillouin‐flow beam, that the radial rf current distribution in the beam is the same as that of a beam whose modulation is represented as sinusoidal scallops on a beam of constant (volume) charge density. As either α or the focusing field, or both, are increased, the rf current is no longer confined to the beam periphery but becomes more evenly distributed throughout the beam cross section.
展开▼
