Extreme High Voltage: Improved Vacuum Glow Discharge Demonstration
I installed a little ball valve and some better fittings in the vacuum line and vastly improved the tightness of the system.
I can go for tens of minutes now with the pump off and the valve closed before the air leaks in enough to quench activity. And this also means that the pump pulls down faster and to a lower ultimate pressure, which of course once again changes the character of the glow discharge plasmas.
The driver is the same one I used for my earlier Jacob’s Ladder videos. It uses 2 ea. IRFP260 mosfets on small heatsinks in a Zero-Voltage Switching (ZVS) circuit and seems very robust. I haven’t managed to blow any of its components since I built it, although I did blow out a flyback transformer by leaving it running for too long while distracted by teh internest.
For the hot arcs at ambient pressure in the Jacob’s Ladder I use 24 volts supply and fuse the input at 7 1/2 amps. In this glow application the system “only” draws 6 amps or so at 24 volts input, depending on the level of the vacuum.
I am amazed that the driver will actually still oscillate and supply enough power for the glow at an input of only 5 or 5.5 volts. The mosfets clearly won’t be turning fully on at that low gate drive voltage and so will be dissipating a lot of the input power internally; it won’t even be getting to the glow itself.
I am still “floating” the grid; it’s not hardwired to anything yet. Next I’ll be putting in another feedthru and some connecting wiring for the grid or other active element.