Click to embiggen vastly
If it looks like a miniature sun, maybe that’s because on one level it is – it’s creating plasma, which surrounds it like a corona around the sun. This plasma is being generated by an electrical current, of course, and not a vast fusion reaction in space.
You can read more about what’s going on in this page on how ionization tubes work in an electric circuit. They’re related to neon lights – fill what would be a vacuum tube up with a particular gas, and an electric current will excite that gas until it starts to glow.
I found this photo on Wikimedia Commons.