Radio Frequency Amplification in a Linear Crossed-Field Amplifier Using Cold Cathodes

A low-frequency (561 MHz), injected beam, and linear format crossed-field amplifier (CFA) using gated field emission arrays (GFEAs) has been experimentally studied and compared with simulation. The CFA uses a copper wire on Teflon meander line circuit with retardation of ~21. Eight silicon tip GFEA dies were used as the injected electron source to provide up to 160 mA. A segmented end-collector system (nine electrodes) was used to measure the spatial variation of the beam current with and without gain. A gain of ~5.5 dB was measured for a sole-circuit voltage of -2.9 kV, an injected beam current of ~160 mA, an applied magnetic field of 0.0125 T, a radio frequency (RF) input power of 15 W, and a sole-circuit gap of 2 cm. A CST particle in-cell model shows a high gain (~1-2 dB) than the experiment, but the gain variation versus injected current, voltage, and magnetic field matches well. Variation with RF input power shows a significant decrease in gain above 15 W in the experiment with the decrease seen in simulation observed after 25 W. Analysis of the end-collector current shows a rapid decrease after 12 W in the experiment and 25 W in the simulation. This result occurs because the highly cycloidal electrons are close to the CFA circuit and get collected on the circuit before providing amplification energy. This observation is confirmed in simulation, which shows that the current going to the circuit rapidly increases and the end-collector current rapidly decreases. This effect also accounts for the higher gain observed in simulation. These experiments provide a basis for using gated field emitters to study beam-wave interactions in microwave vacuum electron devices.