Plasma torch electrode structure

An electrode structure for decreasing the ampere to volts ratio of the operating power for a plasma torch comprising a cathode, an hollow annular anode structure including an anode electrode at a downstream end of said anode structure remote from said cathode, a gas passage, an interior of said hollow anode structure defining a portion of a circumferential wall of said passage, said gas passage being symmetrical relative to a longitudinal axis of said electrode structure and extending around a portion of said cathode and from said cathode through said hollow anode structure to said anode electrode, said cathode having a cathode tip concentric with said passage, means for introducing gas into said passage for flow around said portion of said cathode, past said cathode tip and through said hollow anode structure, said hollow anode structure further including a restriction means defining the cross sectional size of a portion of said passage through said anode structure between said cathode and said anode electrode, said restriction means having an upstream section adjacent to said cathode tip, a downstream section remote from said cathode tip and a throat section therebetween, said throat section defining a section of said passage having a minimum cross sectional area, said upstream section being spaced downstream in the direction of gas flow from said cathode by a distance to form a first portion of said passage between said cathode and said restriction means, said first portion of said passage having a first cross sectional area, the ratio of said first cross sectional area to said minimum cross sectional area being at least 2 to 1, said downstream section of said restriction means terminating at said anode electrode, said upstream section of said restriction means having a shape that gradually and smoothing constricts the cross sectional area of said passage from said first cross sectional area to said minimum in said throat section and is shaped to accelerate the velocity of gas flowing through said passage which flow is also accelerated by heating and expansion in said passage so that the gas flow velocity through said restriction means is sufficient to carry an arc between said cathode tip through said restriction means and to confine said arc for passage through said throat section, said downstream section being shaped to gradually expand the cross sectional area of said passage from a downstream end of said throat to said anode electrode so that said arc may discharge to said anode electrode whereby said arc may extend between said cathode and said anode cathode and pass through said restriction means while being constrained and spaced from walls of said passage by said gas flow and said ampere to volts ratio is reduced relative to a similar electrode structure without restriction means.