A double take on the double arc

A double take on the double arc. More than just a tool for movie stars to break into a vault, the plasma cutting torch has many industrial uses, as depicted here. In plasma cutting, an electric arc is established between a cathode on the torch and the metal workpiece, which acts as the anode. A collimated gas stream blows at high speed through a conducting nozzle in the torch and, in the presence of the arc, becomes the high-temperature plasma that melts through the metal. The nozzle can be damaged if the arc, instead of passing through the orifice, contacts the wall and then jumps onto the workpiece. That so-called double arc has also been seen in a transient, nondestructive form that spikes in milliseconds; neither form is well understood. A trio of researchers in Argentina has now studied the nondestructive double arc experimentally, using the nozzle as a probe...