Today I did a full 10 capacitor 450V test fire of the coil power supply into the coils:
No problems, everything went well.
On a disappointing note… it looks like Goddamn vacuum pump is broken again: the vent value going into the turbo pump is stuck open, allowing atmosphere to flow into the chamber. Maybe I fried the valve with a voltage spike.
Prometheus Fusion Perfection 
Great! You should grab a digitizing scope, or a analog scope and camera; in order to record the voltage and current profile. This can serve as a reference that can be used later to see if the capacitors are degrading; or pin hole openings in the magnet insulation are occurring.
It’s just a good idea to checkpoint the experiment for troubleshooting later; or even preventing problems in the first place.
If you didn’t do it directly the valve is probably physically okay (well might be); that would leave the coil insulation being ruptured by a spike. This would probably mean a short possibly being voltage dependent; when I say things like “possibly” it means >30% chance, but most likely of the things I can imagine:)
Of course there are other possibilities; long wires having enough pick-up to pin weld the armature and such.
You might take any long wires laying around, including the coils, and make sure they are suppressed to a moderate voltage. Protecting against the magnetic field you are generating and the electrical impulse generated by arcs.
My process would be to make every extended circuit a twisted pair for drive and return. Put balums (just wraps of the pair through a toroid) on each of the pairs. Then put TVS diodes across the drive/return pair; and then TVS diodes to a reliable ground where raising the voltage of the ground 10-100V will not have any affect on anything. i.e. a ground tree. That is for everything that is not a A/D D/A signal; those have to handled more carefully.
Let it be know, I am considered excessively paranoid; and exasperate people. Over 90% of the time these things do nothing; but the 10% can be a real problem if not taken care of. You can always undo the TVS’s/Balums if you want to see if they are needed.
IMHO:A strong streak of paranoia is the mark of a good designer.
These valves typically are open when unpowered. Maybe the supply is dead. coil resistance will tell you if its dead. They also have an allen key adjustment to set the purge flow. You can set this to zero I think which may get you up and running again.
Good luck.
Dustin
You are my hero. I hope to be an evil genius with a well appointed lab some day as well :D
:)