Simulations for electron emission and maximum current output from metal emitter arrays

Date

2021-08

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Abstract

High electron emission is an important source for high power microwave systems. High electron emission is an important source for high power microwave systems. Here the physics of current output starting from cathode emission, followed by transport of the electron swarm to generate a time-dependent current is analyzed through simulations, with comprehensive inclusion of several related physical mechanisms. For electron emission, both an applied DC bias and a combination of a DC field and superimposed laser field are probed. For the latter, heating at the electrode surface and its effects on a nonequilibrium electron distribution is included based on appropriate rate-equation analyses with energy balance. Next, a Molecular Dynamics scheme for time-dependent numerical calculations of total current for emitter arrays is developed. It includes many-body Coulombic contributions from the electron swarm, geometric field enhancements with shielding based on a Line Charge Model, and dynamic screening due to the evolution of the swarm in position and velocity space. Several physical details such as the material-dependent workfunction and evolution of the internal space-charge fields are incorporated for completeness. Numerical evaluations are applied to different multi-emitter array arrangements having a hexagonal lattice, for both identical emitters and bimodal populations. For a bimodal distribution, output current optimization is shown for alternating arrangements with three or more successive emitters of the same length along primitive axes. Finally, for completeness, evaluations of electron current output from tungsten emitter arrays with Cs and CsI coatings are also carried out.


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Keywords

Photoemission, Emitting Array, Laser and DC Fields, Carrier Heating, Field Emission, Dynamic Screening, Many-Body Dynamics, Bimodal Arrays, Emitter Coating

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