Phase pulse generator

The Phase Pulse Generators are devices built by the Forerunners into their Halo installations. Halo's main weapon is powered by three phase pulse generators. 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 (Electro Magnetic Pulse) 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 first Halo, 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 can be found on the last level of Halo 3, Halo. These generators were likely destroyed in the resulting chaos of the installation's firing sequence, this could explain why the Master Chief was not killed by the energy pulse seen racing past him in Halo's final cutscene.

Delta Halo
It is not known where the generators are. It is possible that unlike Alpha Halo, it uses only one generator, within the Control Room itself.