Negative plasma potential relative to electron-emitting surfaces
- 9 September 2013
- journal article
- Published by American Physical Society (APS) in Physical Review E
- Vol. 88 (3), 033103
- https://doi.org/10.1103/physreve.88.033103
Abstract
Most works on plasma-wall interaction predict that with strong electron emission, a nonmonotonic “space-charge-limited” (SCL) sheath forms where the plasma potential is positive relative to the wall. We show that a fundamentally different sheath structure is possible where 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 plasma and the ion wall flux is zero. An analytical solution of the “inverse sheath” regime is demonstrated for a general plasma-wall system where the plasma electrons and emitted electrons are Maxwellian with different temperatures. Implications of the inverse sheath effect are that (a) the plasma potential is negative, (b) ion sputtering vanishes, (c) no charge is lost at the wall, and (d) the electron energy flux is thermal. To test empirically what type of sheath structure forms under strong emission, a full plasma bounded by strongly emitting walls is simulated. It is found that inverse sheaths form at the walls and ions are confined in the plasma. This result differs from past particle-in-cell simulation studies of emission which contain an artificial “source sheath” that accelerates ions to the wall, leading to a SCL sheath at high emission intensity.Keywords
This publication has 32 references indexed in Scilit:
- Experimental study of a photoelectron sheathPhysics of Plasmas, 2012
- Breakdown of a Space Charge Limited Regime of a Sheath in a Weakly Collisional Plasma Bounded by Walls with Secondary Electron EmissionPhysical Review Letters, 2009
- Kinetics of a low-density plasma near a dielectric surface with account for secondary electron emissionPlasma Physics Reports, 2007
- Sheath Physics and Boundary Conditions for Edge PlasmasContributions to Plasma Physics, 2004
- The influence of electron emission on heat load to the plasma facing materials under space charge limited condition with an oblique magnetic fieldJournal of Nuclear Materials, 1999
- Secondary electron emission at anode, cathode, and floating plasma-facing surfacesJournal of Applied Physics, 1996
- Fully kinetic plasma-sheath theory for a cold-electron emitting surfacePhysics of Fluids B: Plasma Physics, 1992
- Real time, in-situ measurements of secondary electron emission in DITEJournal of Nuclear Materials, 1990
- Potentials of surfaces in spaceReports on Progress in Physics, 1981
- The Interaction of Electron and Positive Ion Space Charges in Cathode SheathsPhysical Review B, 1929