Research on thermionic plasmas. Final report, 15 January 1983-30 June 1984

Technical Report · Wed Jun 13 04:00:00 EDT 1984

OSTI ID:5841885

Main, G L; Lam, S H

Emitter sheath phenomena are important in thermionic energy converters 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 converter 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 reduces 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 converter formulation, all three of these phenomena (which become significant at low currents) steepen the current-voltage characteristic.

• Research Organization: Princeton Univ., NJ (USA). Dept. of Mechanical and Aerospace Engineering
• OSTI ID: 5841885
• Report Number(s): AD-A-150663/3/XAB
• Country of Publication: United States
• Language: English

Related Subjects

30 DIRECT ENERGY CONVERSION
300403* -- Thermionic Converters-- Materials
Components
& Auxiliaries
CHARGED PARTICLES
DENSITY
DIRECT ENERGY CONVERTERS
DISTRIBUTION
EMISSION
IONS
NESDPS Office of Nuclear Energy Space and Defense Power Systems
PHYSICAL PROPERTIES
PLASMA SHEATH
REFLECTION
RESEARCH PROGRAMS
THERMIONIC CONVERTERS
THERMIONIC EMISSION