Asgard plasma beam weapon

"...the Apollo and the Daedalus have been retrofitted with the new Asgard plasma beam weapon which—given—are very, very powerful..."

- Rodney McKay

Plasma beam weapons are a newly developed technology created by the Asgard shortly before their extinction and gifted to the Tau'ri as part of their legacy. They appear far superior to the older Asgard weapons.

Overview
"At least we now have weapons we know will destroy an Ori ship."

- Cameron Mitchell

Instead of firing pulses of energy like most beam weapons, Asgard plasma beam weapons release a narrow, high-intensity beam of superheated plasma. Just one of these beams is capable of overloading and penetrating even the most advanced shields and burning through the hulls and internal structures of an enemy vessel with comparative ease, causing heavy damage; if the beam hits a critical area the target can be destroyed in only two to three shots. This incredible ship-to-ship weapon might be one of the most powerful and efficient ever encountered, easily comparable to the Ancient Drone weapons, although they work quite differently.

While there are beam weapons that can discharge more raw power at once such as the Lagrangian Point satellite (which is almost the size of a Ha'tak vessel - certainly not a ship-based weapon) require an extended period of time and a significant amount of power to charge. In contrast, the advantage of the more advanced plasma beam weapons lies in their ability to come online and charge at an incredibly rapid rate (using up relatively little power in the process) and deliver several consecutive shots in only a few seconds, overwhelming enemy defenses while they are still recovering from the previous hits. Only one ship has ever been able to withstand this weapon; Goa'uld-shields can be overwhelmed by a single beam while the powerful shields on Ori warships starts to fluctuate greatly after 2 hits. After 3-4 hits the shield will fail and the ship it self will receive so much damage it gets crippled. Any further hits will make the warship explode. Not even the most advanced shields on the Aurora-class battleships, the most advanced Ancient battleships, can not withstand to many hits from the Asgard plasma beams before they fail. To date only a ZPM-enhanced Wraith Hive ship has been able to withstand plasma beams with minimal damage.

Asgard plasma beam weapons have been proven capable of easily destroying Ori warships (although Odyssey has one Zero Point Module) in 6 hits, Asuran Aurora-class battleships, in 9 hits (although one was destroyed in two hits, but it may have been damaged at the time), and Wraith Hive ships in three hits. The Super-hive, equipped with ZPMs, however, are virtually immune to these weapons, due to the far greater density of their hull. A direct hit will only result in minimal damage.

The weapon's power may be adjustable since it has been observed disabling a Wraith cruiser instead of destroying it. However, this may have also been managed instead by selective targeting.

History
"I want to be able to brief the President as soon as we get back. He's gonna want to know how quickly we can duplicate this new Asgard weaponry."

- Henry Landry

These weapons were placed on the Odyssey as a gift to the Tau'ri in a mass upgrade which included all the knowledge of the Asgard, providing the ship with a means to effectively fight the Ori warships that had been invading the Milky Way galaxy. They were first used when the Odyssey couldn't get to hyperspace in time while chased by an Ori ship and proved their worth by destroying it in their very first use. Later, they were used to destroy another mothership. These weapons were eventually equipped on both the Daedalus and the Apollo, which put them to use almost immediately when they used them to rapidly destroy the Aurora-class warships that the Asurans were deploying in the Pegasus galaxy. They saw great use in the Battle of Asuras in which they destroyed several battleships. Since then, all Daedalus-class warships have been outfitted with these weapons.

In an alternate timeline, plasma beam weapons were also equipped on the Phoenix, and used to quickly destroy several Hive ships under Michael Kenmore's command.

They saw action in the Battle of M2S-445, where they disabled Michael's cruiser's hyperdrive before destroying it as soon as Teyla Emmagan was rescued from the ship. They were later used in the Battle of the Super-hive, but were largely ineffective against the upgraded Hive due to its much-improved hull armor, with a direct hit resulting only in minimal damage.

During the Battle of M35-117 in an alternate reality, an alternate Daedalus attacked an Alien ship with these weapons. While the few shots it was able to get off due to great lack of power weren't enough to destroy the alien ship, it disabled the ship's weapons and saved the alternate Atlantis.

Behind the scenes
It has been implied by both the Stargate Universe series and by Joseph Mallozzi in his blog that the shields on Lucian Alliance Ha'taks have been upgraded to resist these weapons. However, the exact degree of resistance is unknown.

Even so, the beam weapons are never seen to be fired against a Ha'tak type vessel. Given the extreme extent of power these weapons have, it is most probable that the shows writers simply decided to not use them, to allow the Lucian Alliance at least some level of threat.