Actually, what has to balance is force averaged over time to get zero net accleration. In a future generator, we expect 10 GG fields in a roughly 10 micron radius plasmoid lasting several ns and repeated 200 times a second or so. You do the math. It works out to average forces of around a kN–not so much. In other words, huge pressures in a very tiny volume for a very short time works out to not very much average force. But you get good burn up and net energy.
