The Princeton Plasma Physics Lab used flywheel storage to power the massive draw needed by the fusion test reactors. The flywheels were in a vast hall, each in it’s own vacuum housing. I asked how far one would go if it broke free. The answer I got was “Philadelphia.”
—”Princeton Plasma Physics Lab used flywheel storage to power the massive draw needed”
Looking around, I found this...
Up and away: The two 700-ton flywheels that power the NSTX-U could put a naval ship into orbit.
https://www.pppl.gov/node/3485
Homopolar Generator?