ABSTRACT An investigation is reported of virtual cathode formation and hysteresis effects in electron beams produced by microwave low-noise electron guns in the presence of a strong longitudinal magnetic field. It is shown that, contrary to earlier suggestions, positive ions are not necessary for the formation of a hysteresis loop but they may greatly affect its size. Under certain conditions more than one virtual cathode may form, giving rise to additional effects.

Measurements of the noise parameters S and II for an electron beam are described. Observations of the standing-wave pattern of noise on the beam show that at high axial magnetic fields the noise space-charge waves decay.

The design of a constant-current 30 A 4 kw d.c. power supply is described. A bridge rectifier incorporating silicon controlled rectifiers is followed by a low-pass filter and a series control element consisting of several power transistors in parallel. The current is controlled, and stabilization is provided, by the series transistors. By altering the firing angle of the rectifiers the bridge output voltage is controlled in such a way as to maintain a low collector voltage and a low transistor dissipation. The output current can be maintained constant to better than 0.1% at any value between 5 and 30 A. At maximum output the efficiency is 83% and the input power factor is 0.85 lagging.