There are many ways to create plasma, in order to generate plasma, you must create an environment where electrons want to break away from molecules, ionization, an collect into a defined space. Fire is a form of plasma, dont believe me try running high voltage in open air, and through fire. You will see the Arc start at a greater distance when it passes through fire. Fire is a plasma because the heat generated increases the electron energy to the point where it escapes the atom its attached to until it cools down. The light you see is when the electron goes from the higher energy state to a lower one, when it releases that energy a photon is created and that is the light that we see.
You can also create plasma from creating a high potential charge difference between two points, high voltage, that the air between it gets influenced by a high electric field that the electron gets stripped from the atom as it flies to the positive end of the wire. Vice-versa the atom is now positively charged that it will fly to the negative end of the electrode.
Now you have free flowing electrons, the electrons are then influenced by the magnetic field, causing it to bend perpendicular to its direction of travel. In this case the flow of electrons is the near the same as the magnetic field, so the bending effect is minimal, and you only see it in a spiral.
Oh and it plays music.