Optically pumped cesium plasma neutralization of space charge in photon-enhanced thermionic energy converters

Photon-enhanced thermionic emission from semiconducting cathodes is a promising means of increasing cathode current density in low temperature vacuum thermionic energy devices [J. W. Schwede et al., Nature Mater. 9, 762 (2010)]. However, the space charge resulting from high emission current densities prevents emitted electrons from reaching the collector, even with gaps as small as 100 μm and at voltages as high as 1 V. We demonstrate by particle-in-cell simulations that one possible solution to overcoming the space charge is to add cesium filling and generation of a space charge-neutralizing plasma by continuous laser excitation of the cesium resonance level.