Non-classical plasma sheaths: space-charge-limited and inverse regimes under strong emission from surfaces

The collisionless plasma sheath represents an important example of Vlasov theory application. In this study, Particle-in-Cell/Monte Carlo Collision methodology has been used to study different examples of plasma sheaths under strong negative charge emission from surface. Secondary electrons emitted by primary electrons (acceleration region of Hall-effect discharge) and by photons (dusty plasma) are responsible for a complete inverse sheath: the potential monotonically increases toward a positively charged wall that is shielded by a single layer of negative charge. No ion-accelerating presheath exists in the bulk plasma region and the ion flux at the wall is zero. In the case of production of hydrogen negative ions by neutral conversion on the plasma grid in the extraction region of a negative ion source, a space-charge-limited regime occurs with the formation of a non-monotonic double layer in front of the grid.