Arthur's Mantle was the Arthurian name given to the interdimensional device, which Merlin used to hide from the Ascended Ancients known as the Others. The mantle contained logs on all his research on an anti-Ascended weapon that he created to fight and destroy the Ori.
Functions and abilities
When initialized, the device would release lepton radiation to pull those within close proximity to the device into an alternate dimension, similar to the one occupied by the Omeyocan and visible to those who wear the Sodan Invisibility device. Whoever was pulled into this dimension was out-of-phase, and thus able to walk through objects that are in-phase. The only thing such a person could manipulate was the device itself. After being pulled into the other dimension, a person could view Merlin's log, which included technical specifications regarding construction and location of the Sangraal - a weapon capable of destroying ascended beings, intended by Merlin to neutralize the Ori. After pushing a combination in the holographic display, every person pulled into the other dimension would then be instantly pulled back into their home dimension, even if they were on another planet, as the device maintains a subspace link with them. (SG1: "Arthur's Mantle")
The device was built by Merlin/Moros, after he retook human form, in order to hide his research into destroying Ascended beings from the other Ascended Ancients who would try to stop him. It was later stored in the Avalon cave under Glastonbury Tor in England. There it was found by SG-1 who at first didn't known what it was. After some months however, Lt. Colonel Samantha Carter accidentally activated it and pulled herself and Lt. Colonel Cameron Mitchell into the other dimension. Later, Dr. Daniel Jackson was also pulled into this dimension, and it was he who translated the text of the log. He was also able to bring the three of them back before the energy of the device was depleted. (SG1: "Arthur's Mantle")
The device was later used by SG-1 to hide a whole village on P9C-882 from the Ori by powering the device with three Naquadah generators. Due to damage to the generators, this failed, but they were able to use the power source from an Ori staff weapon to do the job. (SG1: "Line in the Sand")
In an alternate reality which Carter was pulled into, she used the device to pull the whole planet Earth out-of-phase by supplying it with over 90% of the entire United States of America's power grid. That world then located their version of the device but lacked the knowledge to use it, so they decided to keep Carter in their universe. She later returned into her native reality. (SG1: "The Road Not Taken")