Regarding "energizers", they're likely anything that provides energy to any shipboard system. In the modern navy and industrial terminology, "energizing" or to "energize" equipment means to power equipment with electricity.
The Enterprise has been referred to having "main energizers" and what I would imagine as some kind emergency or auxiliary energizers (aka "auxiliary power" as Saavik switches to that after losing the main energizer during a simulation in ST2.)
I don't believe the energizers would be directly used to heat up antimatter though. Instead the energizers would energize the antimatter thermal regulators