Evaluation of electron currents from cesium-coated tungsten emitter arrays with inclusion of space charge effects, workfunction changes, and screening

Abstract

Evaluations of electron current output from tungsten emitter arrays with Cs and CsI coatings are carried out. The approach is based on first-principles calculations of the material physics including evaluation of the internal potentials, electronic wavefunctions, tunneling probabilities, and work function to predict field emission currents. This is coupled to time-dependent kinetic simulations for the assessment of emitter array currents with an inclusion of many-body Coulomb contributions from the electron swarm, geometric field enhancements with shielding based on a line charge model and dynamic screening from the swarm. Our numerical evaluations for arrays with a hexagonal lattice show the expected role of field screening with reductions in emitter separation. For scaling with emitter number, the results indicate nearest neighbor separations of more than 2.5 times the emitter height, in keeping with previous reports.