Time Vector Generator

A Time Vector Generator was a component of a TARDIS that made it dimensionally transcendental. Removal of the Time Vector Generator would collapse its interior into an alternate dimension, leaving only the exo-shell and making it the same size on the inside as the outside. As the Second Doctor succinctly put it, removal of the TVG turned the TARDIS interior "into an ordinary telephone box again". (TV: The Wheel in Space)

It resembled a long ebony wand and was a powerful energy source.

Removal of the TVG turned the inside of the TARDIS shell into an anechoic chamber, which is how the Doctor tricked Atimkos into destroying himself. (PROSE: Invasion of the Cat-People)

The Doctor removed the TVG when the fluid links exploded, filling the TARDIS with mercury fumes. The TVG was later used to boost Space Station W3's x-ray laser to defeat the Cybermen. (TV: The Wheel in Space)

Jared Khan attempted to steal the TVG from Bernice Summerfield on behalf of his masters, the Charrl. (PROSE: Birthright)