Arcs at reduced pressure behave differently than at atmospheric pressure. They produce a dim glow instead of a thin arc and they are much longer. You can make your own homemade plasma jar (fusor) yourself. As a low-pressure chamber I used a glass jar with sealing cap. I used the compressor from an old refrigerator to evacuate the jar. Although it does not create too much vacuum, only about 5kPa, but still allows a lot of interesting experiments. The jar is of course connected to the suction side! :-). One electrode is formed by metal glass cap and a second one is formed by piece of foil glued to its bottom (RF current passes through the glass). As a high frequency high voltage supply you can use the high voltage transformer from and old black and white television (transformer with no rectifier) with any driver. I am using MOSFET Half Bridge ran from the mains, but suffice even "children's" single transistor driver ran from 12V. The HV supply produces 20kV voltage at the frequency of about 20kHz. Weak arcs occur even when only one electrode (live) is connected. Glass gets very hot from the discharges. When using high-power, this can't be permanently on!