Phase pulse generator
From Halopedia, the Halo wiki
The Phase Pulse Generators are devices built by the Forerunner into their Halo installations. Halo's main weapon is powered by three phase pulse generators.[1] They amplify Halo's signal, and allow it to fire deep into space. The power levels are enormous. How they produce such prodigious amounts of energy is unknown. The generators could possibly emit a gamma ray burst. They are susceptible to close range EMP discharges, and destabilize if they come in contact with an EMP pulse.
They are usually located within the vicinity of the Control Room of the Installation, and the Generator Chambers are usually only accessible by air or via ducts used by the Sentinels.
Cortana had the Master Chief disable these while on Installation 04, in order to delay the Installation's activation so they would have time to destroy it, and to prevent 343 Guilty Spark from "Finding another way of activating Halo."
Two of the pulse generators of the second Installation 04 can be found on the last level of Halo 3, Halo.
