Air plasma cutter is a process that is used to cut steel and other metals of different thicknesses ( or sometimes other materials ) using a plasma torch. In this process, an inert gas ( in some units, use compressed air ) is blown at high speed out of a nozzle: at the same time an electrical arc is formed through that gas from the nozzle to the surface being cut and moves sufficiently fast to blow molten metal away from the cut.

Plasma cutters use a number of methods to start the arc. In some units, the arc is created by cutting the torch in contact with the work piece. Some cutters use a high voltage, high frequency circuit to start the arc. This method has a number disadvantages, including risk of electrocution, difficulty of repair, spark gap maintenance, and the large amount of radio frequency emissions. Plasma cutters working near sensitive electronics, such as CNC hardware or computers, start the pilot arc by other means. The nozzle and electrode are in contact. The nozzle is the cathode, and the electrode is the anode. When the plasma gas begins to flow, the nozzle is blown forward. A third, less common method is capacitive discharge into the primary circuit via a silicon controlled rectifier.