DC plasma arc generator with erosion control and method of operation

A method of operating a DC plasma arc generator, said generator having a cathode, a generally cylindrical anode divided into two portions, a constricting portion and an exit portion, said constricting portion and said exit portion each having distal and proximal ends, said cathode being disposed adjacent said proximal end of said constricting portion, said distal end of said constricting portion being spaced from said proximal end of said exit portion by 0.03 to 0.15 times the length of said exit portion, the length of said constricting portion being 3 to 10 times greater than its inner diameter, the inner diameter of said exit portion being 1.1 to 1.5 times greater then the inner diameter of said constricting portion, said exit portion having a length that is 0.5 to 4 times its diameter, said cathode, said constricting portion and said exit portion being electrically insulated from each other, prior to arc ignition, a refractory metal liner doped with emissive material being disposed within at least said distal end of said constricting portion and said proximal end of said exit portion, and a refractory metal liner disposed within at least said proximal end of said exit portion, said method comprising:

• introducing tangentially a first stream of a vortex-generating gas adjacent said proximal end of said constricting portion to establish a vortical flow of said gas;
• introducing tangentially a second stream of a vortex-generating gas into the space between said distal end of said constricting portion and said proximal end of said exit portion, said second stream intersecting said first stream;
• imposing a potential between said cathode and said exit portion and forming a first arc between said cathode and said distal end of the refractory metal liner in said constricting portion and forming a second arc across the space between said distal end of said refractory metal liner in said constricting portion and said refractory metal liner in said proximal end of said exit portion, said first stream of gas forcing said first arc to revolve about the axis of the constricting portion, said first arc forming a finger which revolves about said distal end of said refractory metal liner in said constricting portion, said second arc forming between said liners at said distal and said proximal ends, respectively, of said constricting portion and said exit portion, said second arc ionizing the gas of the second stream and forcing said finger of said first arc to remain attached to said distal end of said constricting portion.

A method of operating a DC plasma arc generator, said generator having a cathode doped with an emissive material, and a generally cylindrical anode divided into two portions, a constricting portion and an exit portion, said constricting portion and said exit portion each having distal and proximal ends, said cathode being disposed adjacent said proximal end of said constricting portion, said distal end of said constricting portion being spaced a predetermined distance from said proximal end of said exit portion, the inner diameter of said exit portion being greater than the inner diameter of said constricting portion, said cathode, said constricting portion and said exit portion being electrically insulated from each other, prior to arc ignition, a refractory metal liner doped with emissive material being disposed within at least said distal end of said constricting portion and said proximal end of said exit portion, said method comprising:

• introducing tangentially a first stream of a vortex-generating gas adjacent said proximal end of said constricting portion to establish a vortical flow of said gas;
• introducing tangentially a second stream of a vortex-generating gas into the space between said distal end of said constricting portion and said proximal end of said exit portion, said second stream intersecting said first stream;
• imposing a potential between said cathode and said exit portion and forming a first arc between said cathode and said distal end of said refractory metal liner in said constricting portion and forming a second arc in the space between said distal end of said refractory metal liner in said constricting portion and said refractory metal liner in said proximal portion of said exit portion, said first stream of gas forcing said first arc to revolve about the axis of said constricting portion, said first arc forming a finger which revolves about said distal end of said refractory metal liner in said constricting portion, said second arc forming between said liners at said distal and said proximal ends, respectively, of said constricting portion an said exit portion, said second arc ionizing the gas of said second stream and forcing said finger of said first arc to remain attached to said distal end of said constricting portion.