The Tesla Flexion is a device that allows Magicians to communicate across parallel realities.
The Tesla Flexion was created by Fred Flexion and had only been successfully employed once before, as it was deemed too volatile when three people died in an attempt to shut it down.
Learning About Shades
In 2016, it was used by Henry Fogg and Julia Wicker, connecting two different realities temporarily together so that Quentin Coldwater could speak to the Alice Quinn from Timeline 23, one of the sole survivors of the Attack on Brakebills University, who became an expert on Shades.
A New Hope
Months later, Julia and Josh Hoberman were summoned into a Tesla Flexion by Timeline 23's Marina Andrieski and Josh to stop their Beast, who possessed one of the Seven Golden Keys and was massacring Magicians.
The Tesla Flexion is a fold between realities, requiring an array of Tesla coils, ultraviolet lamps, and a tented area for the realities to meet. In the procedure, people from different realities were prohibited from interacting physically, as the collision of matter from different realities occupying the same space can create a paradox, i.e. an explosion. Due to the forces at play in the spell, maintaining a connection for longer than two minutes would result in the death of anyone in the vicinity.