A device designed to facilitate the reaction of vionesium. (TV: Terror of the Vervoids)
Vionesium was a rare and therefore precious mineral. The atmosphere of Mogar made it ideal for mining the mineral and the Hyperion III picked up a shipment from there.
Vionesium reacted with oxygen to produce light and carbon dioxide in large quantities, leading the Sixth Doctor to compare it to magnesium. This reaction compressed all four season, so that they happened all at the same time. The Doctor and Mel used this attribute to speed up the rate of photosynthesis among the Vervoids so that they aged to death. (TV: Terror of the Vervoids)