Stargate

"Large enough for the passage of an entire armada."

- Teal'c

The Supergate (referred to by Bra'tac as the "Chappa'ko") is a massive Stargate developed by the Ori, spanning three to four hundred meters across. All known Supergates have been used for the specific purpose of establishing permanent footholds in distant locations in the universe, permitting the rapid passage of the Ori Army's enormous warships across intergalactic distances. Oddly enough, they seem to use the same programming as was used in Ancient Stargates, and this has proven to give them some vulnerability to tricks using standard Stargates.

Construction
"The gate is composed of individual units. There must be some sort of energy linkage between them, like a chain."

- Samantha Carter Supergates are comprised of 90 individual segments (ships), which are interlinked by a powerful energy field. The blocks are constructed individually, with each being small enough to fit through a normal Stargate.

The Earth vessel Prometheus observed firsthand the formation of the first Supergate inside the Milky Way, at the Free Jaffa world of Kallana. A forcefield created by a Prior on that world expanded over a matter of days to envelop the entire planet and constrict it into a singularity. Rather than transfer the energy required through the Stargate (which Lt. Colonel Samantha Carter believed to be impossible), the Prior provoked both the Tau'ri and Free Jaffa forces into attacking him; the force field was created from the energy expended by their weapons fire. As the planet was contracting, the Supergate's component blocks were sent through the Stargate, forming a ring above the shrinking planet. Due to the intervention of Vala Mal Doran, this Supergate was destroyed before its assembly could be completed.

It is doubtful the second Ori Supergate was constructed in the same way as the first because each piece was considerably larger than a regular Stargate. Since the second Supergate was already complete by the time it was discovered by the Free Jaffa, either some unknown force must have supplied the energy necessary to fuel the forcefield or the Ori found some alternative means to do so, probably building the gate in secret so their plans could not be foiled again. This second Supergate also lay dormant for at least several hours after its completion before the first Ori invasion force came through; this could be due to some necessary part of the assembly process, or simply because the Ori crusaders were in no great rush.

Operation
"With a black hole at either end, they can maintain an open wormhole indefinitely."

- Samantha Carter Both Supergates in the Milky Way have been powered by black holes, which Lt. Colonel Samantha Carter speculated was the only means by which they could be maintained indefinitely. Nonetheless, the Ori do not seem to keep the gate active any longer than is necessary to send their ships through, leaving them inactive most of the time just like a regular Stargate. Indeed, except for their size and the fact that they can apparently only be dialed using an Ori warship, the Supergates apparently function just like their smaller counterparts. It is even possible; though difficult; to connect a wormhole from a standard Stargate to a Supergate.

Thanks to the information provided by Dr. Daniel Jackson from his time as a Prior, Carter developed a way to dial a Supergate using Earth's technology.

Vulnerabilities
"It's working. She disrupted the energy field holding the objects in place."

- Samantha Carter The only known means of destroying a Supergate is to break the chain of connecting segments prior to its completion, disrupting the energy field before the singularity that will serve as its power source can be formed.

All known attempts to disable or destroy a completed Supergate have failed. It was however speculated by Lt. Colonel Samantha Carter that, by placing four Mark IX Nuclear warheads between the parts of the Supergate, the next activation would trigger their detonation and destroy the gate. Since this plan was never carried out, it is not known whether this plan would have worked.

However, it is possible to render a Supergate unusable, as, like a Stargate, there is no way to shut down an incoming wormhole. The crew of the Odyssey, assisted by SG-1 and Dr. Rodney McKay, accomplished this by using a Stargate placed near a black hole in the Pegasus Galaxy to connect to a second gate placed alongside the Supergate, then forcing the wormhole to jump to the Supergate by detonating a series of shaped thermonuclear charges (and a Wraith Hive ship). The power fed into the Pegasus Stargate by the black hole allowed the wormhole to be maintained indefinitely, thus preventing incoming wormholes from the Ori galaxy. .

The Supergate remained unusable until the Pegasus Stargate was destroyed by the Daedalus to allow SG-1 to send the Sangraal to the Ori home galaxy. The Ori Army was then able to re-secure the device and sent seven ships through to the Milky Way.

First Supergate
After a Prior was sent to Kallana in an attempt to convert its people, the Jaffa living there refused to accept the Ori as gods. Realizing that the Jaffa living on the planet would never convert, the Prior erected an energy shield around both himself and the still active Stargate, designed to crush the mass of the planet into a micro black hole.

However, as even the Ori were unable to project enough energy through a Stargate to both sustain a wormhole across galaxies and maintain a shield large enough to encompass an entire planet, they were forced to rely on outside help to provide the necessary energy. Knowing both the Free Jaffa Nation and Stargate Command would react, they convinced Nerus to relay information regarding the invasion to SG-1, who subsequently sent the Prometheus to the planet.

Playing right into the Ori's hands, SG-1 and several Ha'taks fired on the force field and detonated a Mark IX Nuclear warhead inside the shield. Their combined efforts provided enough energy to allow the shield to completely envelop the planet, which subsequently crushed the planet into a micro black hole. In the meantime, the Supergate's individual modules had been sent through the conventional Stargate, each component flying autonomously up into nearby space to self-assemble into the Supergate's ring.

When SG-1 eventually realized they had been taken advantage of, Vala Mal Doran inserted a Goa'uld Tel'tak in place of the last link of the gate, causing a power surge that prevented the completion of the device. However, she was unable to ring back to the Prometheus before the modules were destroyed, and as the matter stream was sucked into the black hole, Vala was transported to the Ori home galaxy instead.

The leftover black hole was eventually used by the SG-1 from an alternate reality as a means to travel between universes by directing the Stargate's wormhole through it. However, due to the attempt, Earth had become a hub for several different alternate realities, with teams from several alternate universes arriving at the SGC. Although the alternate SG-1 nearly succeeded in accomplishing their mission, to steal Atlantis's Zero Point Module, they were eventually sent back to their proper realities.

Second Supergate
"Somewhere out there, the Ori have a working Supergate."

- Vala Mal Doran As Vala Mal Doran, who was transported to the Ori home galaxy several months earlier, was aware of the Ori's recent plans to send another invasion fleet to the Milky Way, she used a Long-range communication device to warn Stargate Command about the successful completion of a second Supergate.

After the Supergate was discovered near P3Y-229, the SGC dispatched the Odyssey to join a large contingent of the Free Jaffa Nation's Ha'tak ships which had been trying to destroy the Supergate to no avail. Although Lt. Colonel Samantha Carter unsuccessfully attempted to activate the Supergate before the Ori dialed in, effectively blocking them out, the gate activated. In what would later become known as the Battle of P3Y-229, four Ori warships emerged, laying waste to everything that stood in their way.

However, several weeks later, SG-1 was able to activate the Supergate in order to prevent additional battleships from gating to the Milky Way. SG-1 positioned a Milky Way Stargate next to the Supergate, and another Milky Way Stargate near a black hole in the Pegasus galaxy. They subsequently dialed from Pegasus to the Milky Way, using a nuclear warhead to cause the wormhole to jump from the Stargate to the Supergate. Powered by two black holes, the gates could remain connected indefinitely. In the process, an Ori warship was destroyed by the giant vortex of the activating Supergate, while a Wraith Hive ship was destroyed at the other end to provide the energy to make the wormhole 'jump' in the first place, scoring a triple victory against some of humanity's greatest foes.

The Supergate was deactivated several months later, when the Stargate in the Pegasus galaxy it was connected to was destroyed by a Mark IX warhead deployed from the Daedalus. Under the instructions of Dr. Daniel Jackson, who had managed to infiltrate the Ori by allowing himself to be transformed into a Prior, the Supergate subsequently was 'dialled' to connect to the Ori home galaxy, and an Ori warship was sent through, along with an activated Sangraal in order to destroy the Ori. Although the plan appeared to be successful, the Supergate was reopened later from the Ori home galaxy, allowing another six Ori warships into the Milky Way to join the seventh that was parked in front of the Supergate.

Later, Carter made plans to destroy the Supergate using four Mark IX warheads but after learning that the Ark of Truth, which SG-1 was searching for, was still in the Ori home galaxy, they decided against it. Instead SG-1 used the Supergate to travel with the Odyssey to the Ori galaxy in hopes of finding the Alteran device. Despite the protests of James Marrick, who was ordered by the International Oversight Advisory to ensure destruction of the Ori galaxy's Supergate, Lt. Colonel Cameron Mitchell decided to leave it intact.

Behind the scenes
The original diameter of the 2nd Supergate concept, is given as 1 mile in the audio commentary of "The Pegasus Project" by William Waring and Jim Menard (Stargate SG-1: The Complete Tenth Season#DVD1). How exactly it was constructed is not known, since the individual pieces are too big to fit through a normal Stargate. It is possible the second Supergate could have been constructed by first creating a smaller (Kallana-style) Supergate, then sending larger segments through that one or just occupying the planet and constructing the segments there. There is also a possible way to destroy the Supergate not noticed by anyone throughout the series. If a Stargate's unstable vortex destroys matter, then activating a Stargate facing a Supergate segment would damage it enough to render the entire Supergate inoperable (however, given how much larger a single Supergate segment is shown to be than a Stargate, multiple vortices may be required.)