An analytical model of an emission-gated Twystrode using a field emitter array

Abstract

An analytical model of a unit cell and of an array of field emitters with a distribution of tip radii is used to estimate the total current and current characteristics on the basis of geometry and materials. Based on the unit cell modeling, analytical estimates of ring cathode inductance, resistance, and capacitance are made to estimate the drive power required to sinusoidally modulate the array in order to produce a bunched electron beam. For a configuration of parameters indicative of a next generation field emitter array (FEA) ring cathode, the characteristics of the array are used to estimate the gain, efficiency, power output, and optimized length of an emission-gated Twystrode (TWT) using a simple model of the beam-wave interaction. The integrated analytical approach and its numerical implementation (“Cassandra”) are validated by comparison to a 1D TWT code (CHRISTINE) which estimates the output power and the optimized length of a TWT. Using “Cassandra,” it is shown that with next generation FEA parameters, interesting and significant levels of performance may be anticipated for a compact, broadband rf inductive output amplifier; in particular, an electronic efficiency of 32% with 15 dB gain may be possible from an array producing 260 mA peak and 71 mA average current at 10 GHz modulation using a helix 1.51 cm long.