A Simulation Study of the Gain Limits of a Crossed-Field Amplifier

The recently available design specifications for the L-4953 crossed-field amplifier (CFA) from Stellant Systems provides an excellent high-power CFA simulation model for studying basic physics of crossed-field devices to improve performance. The L-4953 was recently modeled using VSim and validated against actual device specifications [1]. The maximum gain in the device is ~12 dB, limited by a loss of lock of the main amplifying mode and the onset of an oscillation. Using the VSim simulation model, the parameter space of magnetic field, DC voltage, emission current, frequency, and drive power was characterized with regards to gain, stability, and newly developed diagnostics. These diagnostics and visualizations are used in both the stationary coordinate system and a rotating coordinate system synchronized with the electron spokes. The new diagnostics include electron spoke angle, spoke width, spoke wobble, beat frequency, and electric field spoke alignment comparison. The new visualizations include electron population statistics and electron trajectories. Preliminary results show a 9 kV DC voltage range of stable operation for each magnetic field within the band. The spoke angle in the rotating frame of reference shows a
$\square 45 \square^{\wedge} \circ$
shift from the lowest to the highest stable DC voltages. Unstable operation is distinguished by a modulation of the output power that resembles a beat frequency and often higher gain during the peaks of modulation.