High-power beam-plasma amplifier

The paper describes the interaction of a pulsed power-perveance beam (5 kv, .4a) and a hydrogen plasma to obtain high gain and high efficiency in the S-band amplifier used. A well-formed, pulsed, linear beam in semiconfined flow is passed along the axis of a hydrogen plasma column immersed in a steady, axial magnetic field. The plasma is generated by a double, hot-cathode Penning discharge and is controlled by varying the discharge current and the pressure of the ambient hydrogen gas. Microwave signals are directly coupled to and from the beam-plasma system by gridless-gap cavities. The device described is VacIon pumped and contains a palladium leak tube to act as the source of hydrogen gas. A small-diameter drift tube provides a differential pumping scheme that protects the beam-forming cathode from the high pressures of the plasma region and resulting back-ion bombardment. This arrangement assures long beam-cathode life, repeatable data, and a smooth nonrippling beam entering the beam-plasma interaction region. Results are given for analytical work on the plasma-density profile, and these results used to compute beam-plasma gain for the finite geometry. The experimental data include preliminary diagnosis of plasma density, and gain and efficiency of the device as a function of gas pressure, discharge current, and axial magnetic field.