Thermionic converter
A thermionic converter was a device used in the power distribution facility on Quarra. They operated on a rotating frequency and so had to be closely monitored.

In 2377, Chakotay, while investigating the apparent brainwashing of the  crew on Quarra in the guise of Amal Kotay, was assigned to monitor the thermionic converters. He was the replacement for an expert in thermionic conversion, although he was unaware that the expert was Tuvok, who had left for "health reasons." Chakotay's level 5 aptitude in thermionic conversion made him a suitable substitute, and was apparently substantially better than his skill in microkinetics, rated at a level 3. ()

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Technology