Plasma regulator
From Memory Alpha, the free Star Trek reference.
A plasma regulator (or EPS regulator) is a component of the electro-plasma system of a starship or starbase.
The power conduits of the Cardassian-designed starbase Deep Space 9 had one plasma flow regulator per level. Chief Miles O'Brien suggested an automatic realignment of such a regulator as a possible cause of Ensign Aquino's death in 2369. (DS9: "In the Hands of the Prophets")
Around stardate 50929.4, O'Brien had to recalibrate a shipment of EPS regulators to prevent them from interfering with Deep Space 9's artificial gravity grid. (DS9: "In the Cards")
The plasma flow regulators of the new USS Defiant (ex-São Paulo) were recalibrated by O'Brien's engineering team. (DS9: "What You Leave Behind")
On a Constitution-class starship, plasma regulators were crucial to the functioning of the warp drive. When the USS Defiant arrived in the 22nd century mirror universe, it was sabotaged by the removal of two of its plasma regulators. (ENT: "In a Mirror, Darkly, Part II")
