Phase pulse generator

The Phase Pulse Generators are devices built by the Forerunners into their Halo installations. They are susceptible to close range EMP (Electromagnetic Pulse) discharges, and destabilize if they come in contact with an EMP.

Overview
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.

Installation 04
As mentioned above, the Generators were located close to the Control Room, in platforms accessible via air.

Cortana had the Master Chief John-117 disable these while on the first Halo, in order to delay the Installation's activation so they would have time to destroy it, and to prevent 04-343 Guilty Spark from "Finding another way of activating Halo." They accomplished this by turning the Shield Generators from the Mark V armour he was wearing into a crude yet effective EMP bomb, that once activated knocked out the Master Chief's shielding for a short time.

Installation 05
It is not known where the Installation 05 phase pulse generators are. It is possible that unlike Alpha Halo, it uses only one large generator, within the Control Room itself. This might be a shield generator for Halo, or it may serve as a power source for Halo. However, during the fight between the Arbiter Thel 'Vadam and Tartarus, 343 Guilty Spark states that the "primary generators are coming online."

Installation 04B
Two of the pulse generators are seen during Installation 04B's destruction. Unlike the other generators in the first Installation 04, these can't be destroyed and seem to be more protected, an example of this is that the glass in the room surrounding them is unbreakable and some more barriers have been placed in the perimeter.

These generators also seem to be weaker, as they don't have a continuous beam. The reason for that may be that the Halo wasn't completed at the time. These generators were likely destroyed in the resulting chaos of the Installation's firing sequence, this could explain why the John-117 was not killed by the energy pulse seen racing past him during his escape onboard the.