The Magnetron is a component item added by GraviSuite. Currently, the only use of the Magnetron is in the crafting of the Varja Core (most likely a misspelling of Vajra Core, as that's what is used in crafting) which is only used in the crafting of the Vajra.
NOTE: This is the newest update no longer requires the need of thermal expansion's copper ingot. This now works with any copper. (Needs testing)