St. Elmo's Fire is basically a plasma. Concentrated ionized air will form around highly charged objects. Using a voltage multiplier, a needle tip had been charged with a positive charge and a pick has been charged with a negative charge. Since different charges attract, bringing the two objects together creates a large contraction of charge, forcing the air to ionize and creating a blue/purple plasma of air. For more information about St. Elmo's Fire, please visit the following link. https://en.wikipedia.org/wiki/St._Elmo%27s_fire