Methods for enhancing low-noise CFA performance (crossed-field amplifiers)

Excess noise generation in crossed-field devices is identified with the turbulent flow within the so-called hub region or the space-charge layer close to the cathode emitting surface. For magnetrons, ultralow noise operation is achieved by a decrease in externally supplied filament power to the thermionic emitter. However, in the case of pulsed, re-entrant CFAs (cross-field amplifiers) using secondary emitters, the means for attaining comparable reductions are more elusive, particularly for forward-wave versions of the device. Various methods for enhancing its signal-to-noise performance have been evaluated experimentally with modest success. Provision for RF circuits and geometrical structure such as axially directed grooves in the cathode generally has resulted in noise floor reduction by an order of magnitude. A barreling magnetic field shape of several percent has also demonstrated incremental efficiency improvements, extending the effective range over which the random noise improvement is achieved.<>