Accession Number : ADA148477


Title :   Close-Spaced High Temperature Knudsen Flow.


Descriptive Note : Annual rept. 1 Feb 83-15 May 84,


Corporate Author : RASOR ASSOCIATES INC SUNNYVALE CA


Personal Author(s) : McVey,J B


Full Text : https://apps.dtic.mil/dtic/tr/fulltext/u2/a148477.pdf


Report Date : 15 Jun 1984


Pagination or Media Count : 19


Abstract : This work is a study of discharge processes in Knudsen mode (collisionless), thermionic energy converters. Areas of research involve mechanisms for reducing the effects of electron space charge in such devices. Such mechanisms are essential for thermionic converters to produce useful current and power densities. The mechanisms we have chosen to study are: reduction of space-charge through a very close interelectrode gap (less than 10 microns); transport and retention of positive cesium ions generated by surface ionization; transport of positive cesium ions generated in an arc external to the electrodes; and the mechanism for enhanced current output due to a structured emitter in a mixed barium-cesium vapor. This last process may involve the production of barium-cesium dimer ions. The experimental work used SAVTEC (Self-Adjusting, Versatile Thermionic Energy Converter) diode structures, which were tested in a chamber containing 0.1-1.0 torr of cesium vapor. Comparison of measured volt-ampere curves with theory gave excellent agreement and indicated an interelectrode gap of 6.5 microns at an emitter temperature of 1250 K. A theoretical model of the collisionless thermionic diode was developed which included surface ionization, auxiliary ions from an external source, and trapping of charged particles in potential wells due to infrequent collisions. Studies show that trapping of positive ions leads to a large, beneficial increase in current density.


Descriptors :   *ENERGY CONVERSION , *THERMIONIC CONVERTERS , *KNUDSEN NUMBER , DIODES , IONS , CATIONS , VAPORS , HIGH TEMPERATURE , TRAPPING(CHARGED PARTICLES) , CESIUM , REDUCTION , SURFACE PROPERTIES , ELECTRODES , IONIZATION , EMITTERS , BARIUM , SPACE CHARGE , DIMERS


Subject Categories : Electric Power Production and Distribution


Distribution Statement : APPROVED FOR PUBLIC RELEASE