Jochen's High Voltage Page

Gas discharge with a rotary vane pump

I was lucky enough to obtain an old professional vacuum pump (rotary vane type) - sometimes these are available from scrap yards or electronics recycling firms. Although the pump is old and probably has not been cleaned for many years, it still produces a a very good vacuum compared to e.g. hand pumps or CRT "vacuum reservoirs". The nominal minimal pressure is below 0.1 Torr.

Rotary vane pump (Leybold VP 2).

For the little demonstration below, I used a vacuum vessel made from a clear plastic beaker and aluminum plate. The cup is made of polycarbonate (PC), a very tough kind of plastic that doesn´t shatter. The aluminum base plate serves as one electrode, a second one is made of copper tubing (one end sealed) glued into a hole in the (former ;-) bottom of the beaker. The copper tube serves as a heat sink and can be filled with water from outside for even better cooling. The seal between beaker and plate is made of silicon rubber, the beaker is held in place by atmospheric pressure. The connection to the pump is through a hole in the baseplate, the seal between pump and plate is again made of silicon rubber.

Vacuum vessel made from plastic beaker. Copper tube electrode at the top.

Large Version

Now for the demonstration. The following sequence of pictures was taken at increasing pressure, the power supply was a diode-split flyback driven by my efficient flyback driver circuit. The minimum pressure was achieved only after pumping for some time, and the discharge vessel is probably contaminated by oil vapour. The last picture at perhaps 1/10 atmospheric pressure is a time exposure - the discharge is limited to a narrow tube which moves rapidly around, growing and shrinking in length.

Gas discharge at increasing pressure (left to right).

Large Version
Vacuum vessels may implode. Imploding glass jars are very dangerous - lots of glass fragments flying around. Use proper materials and wear safety goggles and gloves. Put jars behind a clear plastic screen if possible.

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