Based on a few minutes of Googling, I think you're thinking of a plasma cutter which creates a closed circuit through plasma, through a cut line in the conducti

Based on a few minutes of Googling, I think you're thinking of a plasma cutter which creates a closed circuit through plasma, through a cut line in the conductive material, and back to the machine. This seems to be just torches which shoot out plasma at high temperature with no closed circuit required.