The reactor bulb was a sizable, globe-shaped gas collection mechanism. It was situated at the base of Cloud City, a floating Tibanna gas mining settlement suspended within the atmosphere of [Bespin](/article/bespin], a gas giant found in the Outer Rim. As a component of the city's gas extraction process, tractor beams met underneath the bulb, forming an energetic channel. This channel extracted gas from Bespin's lower atmosphere and directed it upwards to the bulb, where it was pushed through an entry point on its bottom surface. From that point, the gas ascended through the reactor stalk and entered multiple reactor shafts, undergoing filtration via processing vanes.
The reactor bulb made its initial, uncredited appearance in the second Star Wars movie, Star Wars: Episode V The Empire Strikes Back, which debuted in 1980. The Legends sourcebook titled Inside the Worlds of Star Wars Trilogy, published in 2004, was the first to identify the device as a reactor bulb. The name was later established as canon in the 2016 reference book Star Wars: Complete Locations, which was a re-release of the 2005 publication Star Wars: Complete Locations.