I am doing a similar project as shown in the video Arcs change shape in my vacuum! RIP Tesla Coil :(. I am working in Tesla coil propulsion. Can anyone explain why this Tesla coil stopped rotating?
The arcs you see in the experiment are basically formed because of motion of electrons from higher potential to lower potential.Near the coil where the potential is high electrons are ejected from the air by ionization and they are thrown out of atom with a certain momentum. So, according to conservation of momentum the atoms are pushed back (similar to recoil of a gun) this atoms or I would prefer to call them ions will hit the wire which is free to rotate about an axis. This makes the wire rotate. Initially, the concentration of atoms around the coil is very high so electrons are ejected at a very high rate but as the air is being pumped out of the container the concentration gradually decreases.So there are no particles left to push the wire.Gradually as all the air is pumped out all electrons in the air are lost so the wire starts rotating.
I would simply say it as Conservation of momentum. I think this clarifies your doubt.