I wanted to create an arc in vacuum with moderate voltage (up to 650VDC), so I bought a vacuum pump.

Next I started working on a vacuum chamber.

After many unsuccessful designs I could finally get something to work.

With this design I could achieve a pressure less than 1mbar, so the next step was to produce a measurable voltage for testing.

After some unsuccessful tries with voltage multipliers and flyback transformers, I built a voltage doubler which outputs around 630VDC while applying 230VAC.

A reading of 625VDC and some lightbulbs as resistance for testing.

Here is a video of the experiment. After selecting 230VAC on the variac and turning on the vacuum pump it took a while to get the pressure and with it the breakdown voltage low enough for the arc to ignite and the lights to turn on.

The next step could be building another vacuum chamber with a larger window and buying a new pressure gauge that can read the actual pressure, also measuring the arc length, voltage and current and also trying to melt some metal powder.

For some reason I was not sure whether there was also heat created with this experiment, but by the later inspection of the screw terminal and wire, signs of heat and melting were clearly visible on one side.