The Great WarEdit
The first psi disrupter was developed by the Terran Confederacy to interfere with the zerg psionic link, fragmenting the Swarm's gestalt and rendering it less effective on the battlefield. It was constructed on Tarsonis but it was not activated during the zerg invasion. The nascent Terran Dominion attempted to locate the disrupter but could not find it; it was thought lost.
The Brood WarEdit
The disrupter nonetheless survived the invasion of Tarsonis and was finally recovered by the United Earth Directorate Expeditionary Force in the Brood War, only to be slated for destruction by order of Admiral Gerard DuGalle. Lieutenant Samir Duran had convinced DuGalle, above the objections of Vice Admiral Alexei Stukov, that the disrupter would undermine the UED's plan to enslave the Overmind. To prevent this Stukov dispatched his own troops to take over the "demolition" of the disrupter, who secretly dismantled and shipped it to Braxis for reassembly.
Stukov's duplicity was soon discovered and a UED strike force led by Duran landed on Braxis with orders from DuGalle to not only destroy the disrupter but execute the Vice Admiral as well. The strike force succeeded in mortally wounding Stukov but before dying he revealed Duran's treacherous nature and successfully appealed to DuGalle to spare and use the disrupter. Duran then attempted to destroy the device by activating the self-destruct, but UED troops were able to foil this attempt in time despite the sudden appearance of zerg forces. A UED garrison was deployed to safeguard the now-active disrupter.
The disrupter proved its worth in the ensuing UED assault and victory on Char. The second Overmind was captured and the UED began taking control of the Swarm in the sector, creating Slave Broods. The effects of the disrupter were widespread and severely weakened Kerrigan's control over her own broods.
Kerrigan rallied the sector's factions suspicious or hostile to the UED to her and, as a first step to ousting the invaders, led them on a strike against the disrupter on Braxis. A small team led by Commander Jim Raynor first destroyed a number of large external power generators feeding the disrupter. With the disrupter offline, Kerrigan used a psi emitter provided by Emperor Arcturus Mengsk to reassert control over local zerg creatures, including a number of special zerg warriors, creating an army which was used to finally destroy the disrupter.
Despite the destruction of the disrupter and the UED force, the legacy of both endured. UED studies had discovered that concentrated doses of sigma radiation could slow zerg movement and reaction speeds by as much as 50%. Subsequent Dominion research confirmed this effect on zerg tissue, and smaller psi disrupters were developed to leverage the effect on the battlefield.
The Second Great WarEdit
During the Second Great War, Doctor Egon Stetmann conducted research into the zerg, and came to the same conclusions as to the effect of sigma radiation on zerg tissue. It would take a lot of work and effort to safely deploy sigma radiation on the battlefield to the extent where zerg would be slowed, but he concluded that it might be worth it. Dominion research later confirmed the findings of Stetmann and the UED researchers, and the Terran Dominion deployed smaller psi disrupters onto the battlefield.
The Brood War game building doesn't have any special abilities.
In StarCraft II: Wings of Liberty, a psi disrupter can be built, unlocked via 25 zerg research points. It decreases the movement and attack speed of all non-heroic zerg units in a small area. This also applies to primal zerg In The Reckoning.
In the final missions of the Wings of Liberty campaign, psi disrupters enhance defenses when co-located at choke points and above ramps; this makes it more difficult for zerg to approach and overrun defenses unscathed. Psi disrupters are less effective against zerg flyers, especially brood lords.
Unlocks the psi disrupter for production/
Studied conducted by the United Earth Directorate have shown that concentrated does of sigma radiation can slow zerg movement and reaction speeds by as much as 50%. The psi disrupter has been developed to constantly emit sigma rays in a large area of effect, making it an essential base defense when facing a large zerg force.
All structures repair themselves to 50% life. All structure fires are automatically put out.
This all-in-one safety system automatically dispatches robotic drones to put out any fires and perform basic repairs on damaged structures. Although these drones are effective at doing basic repairs, they do not have a strong enough AI to perform the more delicate repairs needed to restore a structure past half life.
The psi disrupter was among the last terran buildings designed for Wings of Liberty, alongside the hive mind emulator and automated refinery. Most of these buildings were one-shots with no revisions but had the benefit of getting higher texture polish.
The psi disrupter may have initially been called the "sigma projector."