I took a quick look at the power supply that was used for the ionizer in the liquid scintillation analyzer. It's a Chapman brand 120v input with 5000v output. I believe this is essentially a neon sign transformer with integral ballast/current limiting.
After removing the electrodes i just wired it into my variac to run it upto it's rated 120v input and positioned the output close to the ground wire for some sparkly action. The output is dead on 5000v AC with an input voltage of 120v.
This should make some interesting videos in the future. Especially if i can find some things to zap and also increase the input voltage beyond the 120v rating.