One of my professors gave a two stage rotary vacuum pump to me. Achievable pressure is about 0.5 torr which is good for low pressure discharge experiments. So I started playing with the pump...
I connected the vacuum pump to my Plasma Tube. The right electrode is sealed and connected to the positive, rectified output of my Flyback power supply. The electrode on the right side where the vacuum hose is attached is grounded so there's no discharge in the hose. The picture was taken with the power supply running - you see that these experiments are to be performed in a darkened room.
Three photos of glow discharges at dropping pressures (the bottom one was taken at 0.5 torr). The red part of the discharge is called positive column, the blue part negative glow. They are separated by the Faraday dark space. The negative glow is separated from the negative electrode by the Crookes dark space which can't be seen with the pointy electrodes I use.
Close-up of the positive electrode.
Close-up of the negative electrode. Beautiful, isn't it?
When the pressure is increased again the Faraday dark space grows until the discharge stops.