Mu-field generator

The mu-field generator was a device owned by the Doctor and stored aboard his TARDIS. While visiting the human colony on Frontios, the Fifth Doctor requested that Tegan Jovanka and Vislor Turlough fetch the generator so that he could produce some electricity to power the lights. They were unable to access it as the TARDIS doors leading from the console room into the corridors would not open. (TV: Frontios)