Research on Thermionic Plasmas.
Abstract
Emitter sheath phenomena are important in thermionic energy conventors because the emitter sheath forms the boundary conditions for the plasma in the gap and controls both the ion loss rate and the loss rate of hot (3000 K) plasma electrons to the emitter. This thesis examines three expected emitter sheath phenomena and their effects on conventor performance: (1) reflection of ions coming from the plasma; (2) ions trapped in the double emitter sheath; and (3) surface emission ions. Inclusion of these 3 phenomena combined with elimination of previous sheath approximations requires careful analysis and calculation of the sheath structure. It is shown that the 'Bohm' matching condition must be generalized to insure that self-consistency prevails throughout the entire sheath and not just at the plasma-sheath interface. It is also shown that plasma ion distribution coming into that sheath must have its low energy ions 'cut off' to produce a self-consistent collisionless sheath, and that each of these emitter sheath phenomena reduce the normalized (by plasma density) net loss rate to the emitter. Each of these phenomena also raises the normalized plasma density adjacent to the emitter. The higher plasma density at the emitter causes a greater increase in the loss of hot plasma electron energy to the emitter than the corresponding decrease in the loss of ionization energy (carried by the ions) to the emitter. Therefore these emitter sheath phenomena increase arcdrop. Within the limitations of the current thermionic conventor formulation, all three of these phenomena (which become significant at low currents) steepen the current-voltage characteristic.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jun 13, 1984
- Accession Number
- ADA150663
Entities
People
- G. L. Main
- S. H. Lam
Organizations
- Princeton University