Impact of Coulomb scattering on argon plasma based thermionic converter performance

Particle-in-cell (PIC) simulations were performed to study the impact of Coulomb scattering on the performance of argon plasma based thermionic converters. Using a simplified model, studies from the 1970’s concluded that plasma resistance resulting from Coulomb collisions shifts the IV-curves of thermionic converters that use plasmas to mitigate space charge, thereby strongly limiting their electricity generation capability. In this work the impact of Coulomb collisions in such devices were studied as a function of the relative electrical potential between the electrodes, with higher fidelity than earlier models, using a fully kinetic approach (PIC-MCC with grid based electron–ion scattering). This approach overcomes the incorrect assumption in earlier models that the electron temperature is equal to the cathode temperature in all operating conditions. The fully self-consistent results presented here showed an increase in electron temperature with an increase in gap distance or electrode bias, which decreases the plasma resistivity. It was consequently found that earlier reports overestimated the negative impact of Coulomb collisions at the maximum power point, suggesting the practical usefulness of such devices is higher than previously believed. Electronic conversion efficiency higher than 15% was shown to be feasible at 1200 °C cathode temperature with reasonable electrode work-functions.