You are my hero!!!!!
Are you sure the issue is the plasma? Just to be sure can you run a long file without the plasma on then it only messes up with the plasma on? Using an LCD controller or a laptop?
A few other things it could be but never know.
Someone else just grounded all his metal tubes in the forums, this might help. The wires are shielded, the connections on the solder less mount’s aren’t ideal in this case, maybe solder them up, a metal box for the arduino couldn’t hurt.