Multi-diode converter feasibility experiments
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1994 American Institute of Aeronautics and Astronautics, Inc. All rights reserved. Major handicaps to the use of thermionic diodes are their low voltage, high current output characteristics. The typical performance of a state-of-the-art thermionic diode is approximately 0.5 V at 15 A/cm2regardless of size or geometry. If a compact series combination of thermionic diodes could be fabricated to produce a higher output voltage, the total weight could be reduced and system efficiency improved. In this program the feasibility of constructing a cylindrical thermionic device consisting of a series/parallel combination of small area diodes with a common plasma in a single envelope was demonstrated. Both emitter and collector cylinders were fabricated by outside diameter Chemical Vapor Deposition (CVD) of silicon carbide (Sic) and tungsten (W) on graphite mandrels. The collector was thermally cycled to 1400 C in vacuum four times and remained intact. The resistivity of the Sic was measured from room temperature to 1200 C and found to be sufficient to operate a series/ parallel connection of diodes. No significant reaction was observed with the emitter or W at 1200 C during a 1200 hour life test in a Cs vapor pressure of 2 torr.
