Low-pressure plasma-enhanced behavior of thermionic converters

摘要

High-pressure plasmas have historically been used in thermionic energy converters both to reduce the electrode workfunctions and to mitigate the space-charge effect. The behavior of such devices has been studied extensively, but low-pressure thermionic converters are far less understood. Advances in nanotechnology, such as the possibility to intercalate nanomaterials-based electrodes with alkali metals in order to reduce workfunction, may alleviate the need for high gas pressures; low-pressure devices may thus play a significant role in future if they can address the space-charge problem. Here, we develop the physics of low-pressure thermionic converters by solving the Vlasov-Poisson system of equations self-consistently. We demonstrate that various possibilities arise due to intricate interactions between the spatially varying electron and ion concentrations, leading to phenomena such as plasma oscillations at higher ion fluxes. We show that even a relatively low ion flux density (~5 x 10~(-4) times the flux density of electrons) reduces space-charge significantly and increases the electron current density by a factor of 7. We further extend the model by including electron and ion emission from both the cathode and anode electrodes.