Effects of electron emission on fusion plasma sheath dynamics

The study of plasma-material interactions (PMI) aims to elucidate the complex interplay between thermonuclear plasma exhaust and the solid materials surrounding the plasma. The bombardment of the walls from plasma ions and electrons leads to enormous heat and particle deposition that limits the operational lifetime of the walls while also reducing the performance of the fusion plasma. A specific subset of PMI, electron emission, can significantly alter the region of plasma near the wall known as the sheath. However, many open questions remain in terms of how ion- and electron-induced emission affects the sheath in a fusion reactor. This study uses a continuum kinetic approach to model the plasma sheath near electron emitting surfaces made of tungsten and graphite. Results from the simulations agree with theory that predicts the relative importance of ion- versus electron-induced emission on the sheath structure. Furthermore, it is found that increased emission leads to significantly increased heat and particle flux to the walls. Finally, previous modeling efforts and experimental measurements of the device modeled in this work agree with the simulation results.