Plasma torch preventing gas backflows into the torch

A plasma arc torch is disclosed which has an elongated electrode with an open front and a nozzle with a plasma discharge opening that is coaxial with the electrode. A mounting arrangement includes a ceramic ring that engages the front end of the electrode and a gas ring which concentrically surrounds the ceramic ring. A forward portion of the gas ring, the forward end of the electrode, and the nozzle define a swirl chamber of the torch, and opposing, spaced-apart concentric cylindrical surfaces of the ceramic ring and the gas ring, respectively, form an annulus which extends rearwardly from the swirl chamber. The ceramic ring closes the aft end of the annulus, and the gas ring houses a plurality of plasma gas injection ports which are located immediately forward of the aft end of the annulus. The entire plasma gas for the torch flows from the injection ports generally tangentially into the annulus to prevent a recirculation of gas into the annulus and to impart rotation to the gas after it leaves the ports and as it propagates towards the swirl chamber. The annulus is sufficiently long so that the injected gas spirals through about 5-20 revolutions before it enters the swirl chamber as a substantially uniform, single mass gas flow.