1980s or early 90s era sci fi book, the main character is a woman. The world is now just a mega city around the equator enclosed by a shield or dome, and built generation by generation on top of the ruins of previous cities.
There's a power source generated by the ruins, I think it's called plasma? It lets users astral project and other stuff. The main character finds an unknown well of the stuff and tries to find a buyer, and gets sucked into a political coup of a different area.
Any help is much appreciated.