I believe it's from a book I used to (or still may, somewhere) have called The Star Wars Essential Guide to Vehicles and Vessels--yes, the original, not the new. As for being a solar ionization reactor, assuming a broader interpretation of solar meaning any sun, and based on something I remember reading years ago (so you can totally quote me on this), it's supposed to be a small, self-contained fusion reactor--esentially a small sun inside the vessel. And fusion does indeed involved ionized gas, so.... Yes, it's techno-babble, but that is the reasoning, I'm confident.