ADELPHI, Md. (April 11, 2014) -- Dr. Joshua Smith has simulated the performance of a novel vacuum thermionic engine based on currently available materials in a paper entitled, "Increasing the Efficiency of a Thermionic Engine using a Negative Electron Affinity Collector," which was recently published in the Journal of Applied Physics.

Smith, an Oak Ridge associated universities senior researcher in the Power Components Branch of the Sensors and Electrons Devices Directorate, explained that the primary focus of his paper was to show the plausibility of achieving 20 percent or greater efficiency in a thermionic engine.

Thermionic engines, sometimes called thermionic energy conversion devices or TECs, are similar to vacuum tubes and were studied extensively during the Cold War by scientists both in the United States and the former Soviet Union.

Several prototypes were built, but scientists at the time faced numerous challenges as a result of rudimentary materials selection and fabrication techniques. "The thermionic engine converts heat directly to electricity and is based on a phenomenon called thermionic emission, which is basically the emission of electrons from a heated material," Smith said.

These devices can be very efficient because there's no direct conduction of heat across the device, but past scientists had to contend with a phenomenon known as the negative space charge effect. Since electrons traverse the device in a vacuum, a negative charge builds up within the device and blocks some of the electrons from crossing the device.

As a visiting scientist, Smith works in ARL's Power Components Branch of the Sensors and Electrons Devices Directorate through the post doctoral senior researcher program. The program advertises research opportunities to interested senior researchers in other organizations. ARL has two cooperative agreements; one with Oak Ridge Associated Universities and another with National Academies of Science.


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