Source of Traken

You may be looking for the terraforming device.

The Source was a bioelectronic source of power that the Keeper of Traken, whoever was elected at the time, used to keep the peace in the Traken Union civilisation.

The Source was created by Kwundaar, god of the Trakenites, before being shunned by them and attacked with it, replacing him as their source of guidance. It was described as a sentient sun, shinning light on Traken and destroying any evils that entered its influence by burning them away or turning them into statues, later called Melkurs.

Kwundaar tried to regain his access to the Source and attempted to trick the Fifth Doctor into giving Kwundaar its power, but failed and was overcome by it. The Doctor set up the Keeper of Traken system after Kwundaar damaged some of the Source's components. (AUDIO: Primeval)

The Source was unusual as the Traken Union used it to avert evil. The Melkur took control of the Source from the Consul Kassia, who disappeared when the Melkur materialised in her place. To stop the Melkur, Adric and Nyssa created a servo-shutdown which destabilised the Source, stopping Melkur from controlling it. The Fourth Doctor, after escaping the Decayed Master, cracked the source encryption and reversed it. (TV: The Keeper of Traken)