Capturing the Eidolon Teralyst grants a 12.05% chance to get an Arcane Momentum.
Since any critical hit can trigger the effect, using a Sentinel weapon with a proper sustained critical hit rate is a good way making use of this Arcane (this includes Prime Laser Rifle , Deth Machine Rifle and Sweeper Prime due to its pellet count). It's crucial to use it on a Sentinel with a proper range attack mod like Diriga/Djinn or also Wyrm Prime/Taxon with Eagle Eye on the Sentinel's weapon. As many of their shots miss on mid and high range, it's recommended to avoid using mods like Vicious Spread or Heavy Caliber. Multishot mods, firerate mods and critical chance mods increase the overall trigger rate significantly. None of this works if the player is in a stealth state because being so makes a Sentinel stop firing its weapon at enemies.
This arcane was originally dropped in The Jordas Verdict. Following Update 22.14, all Trial missions were retired from the game and the arcane drops in turn were moved to the Eidolons instead.