Field emitter arrays for plasma and microwave source applications

TLDR

Field emitter arrays (FEAs) promise significant performance gains in compact, low‑power, high‑repetition‑frequency devices due to their instant ON/OFF capability, high brightness, high current density, large transconductance‑to‑capacitance ratio, and low‑voltage operation, and are especially critical for advanced microwave power tubes, micropropulsion electron sources, satellite tethers, and field‑emission displays. This work surveys the key characteristics that make FEAs attractive as cold cathodes for electron beam generation and examines their suitability for microwave applications, particularly in tapered‑helix inductive output amplifiers. An analytical model is developed that starts from field‑emission fundamentals, derives single‑emitter behavior, extends to array operation—including tip emission distribution and space‑charge effects—and applies this framework to evaluate the performance of a tapered‑helix inductive output amplifier.

Abstract

Field emitter arrays (FEAs) stand to strongly impact device performance when physical size, weight, power consumption, beam current, and/or high pulse repetition frequencies are an issue. FEAs are capable of instant ON/OFF performance, high brightness, high current density, large transconductance to capacitance ratio, and low voltage operation characteristics. Advanced microwave power tubes, and in particular, inductive output amplifiers, are by far the most technically challenging use to date. Other important uses include, e.g., electron sources for micropropulsion systems–Hall thrusters–and tethers for satellites, and (the most widely pursued application) field emission displays. The characteristics of field emitters that make them attractive to such applications shall be surveyed. A thorough analytical model of a field emitter array, beginning with a review of the nature of field emission and continuing with an analytical model of a single emitter and the operation of an array of emitters, shall be presented. In particular, attention shall be directed towards those features of FEAs that render them attractive as cold cathode candidates for electron beam generation. Tip characteristics, such as emission distribution, and array operation, such as space charge effects, will be analyzed in the context of the model. Finally, restricting attention to microwave applications, the performance of a tapered-helix inductive output amplifier to highlight the advantages of high frequency emission gating of the electron beam in a power tube shall be investigated.