Plasma gun with adjustable cathode

A plasma generating system characterized by precision controlling of plasma conditions, comprising:

• a plasma gun including:
• a hollow cylindrical anode member;
• a hollow cylindrical intermediate member electrically isolated from and juxtaposed coaxially with the anode member to form a plasma-forming gas passage through the intermediate member and the anode member, the intermediate member comprising a plurality of electrically conductive segments including a forward segment adjacent the anode member, and further comprising insulating means for spacing the segments, the segments being juxtaposed coaxially and held electrically isolated from each other and the anode member by the insulating means, an annular slot being formed between the adjacent segments and between the forward egment and the anode member, the slot being bounded outwardly by the insulating means, and each slot having a radial meander therein such that arc radiation is inhibited form impinging on the insulating means;
• an axially movable rod-shaped cathode member with an anterior cathode tip, the cathode member being located generally in the plasma-forming gas passage coaxially in spaced relationship with the anode nozzle operable to maintain a plasma generating arc between the cathode tip and the anode member;
• a cylindrical rear body member positioned rearwardly adjacent the intermediate member and having a cylindrical cavity therein forming an annular manifold axiallay adjacent the posterior end of the continuous gas passage, the rear body member including a primary gas inlet for introducing plasma-forming gas into the annular manifold;
• a secondary gas means for introducing plasma-folding gas into the plasma-forming gas passage at a location between the primary gas inlet and the anode member, including a forward annular chamber in the intermediate member of substantially larger diameter than that of the continuous passage and a plurality of tangential orifices in the intermediate member for introducing plasma-forming gas with a vortical flow at the circumference of the forward annular region;
• a tubular support member mounted rearwardly adjacent the rear body member;
• and
• a support rod slidably mounted in the tubular support member and having an anterior end with the cathode member attached coaxially thereto, with a drive means coupled to actuate the support rod in axial movement;
• the plasma generating system further comprising;
• primary gas means including a primary gas inlet for introducing plasma-forming gas into the plasma-forming gas passage rearwardly of the cathode tip;
• a source of arc power connected between the anode member and the cathode member;
• and
• voltage determining means for measuring the arc voltage between the cathode member and the anode member, the drive means being electrically connected to the voltage determining means and responsive thereto such that a change in the arc voltage is detected by the voltage determining means and the axial position of the cathode tip is correspondingly adjusted to maintain the predetermined arc voltage;
• wherein the intermediate member is formed substantially with an absence of additional gas introduction into the plasma-forming gas passage.

A method for generating a precision controlled plasma in a plasma gun having a hollow cylindrical anode member, a hollow cylindrical intermediate member formed of electrically conducting material electrically isolated from and juxtaposed coaxially with the anode member to form a plasma-forming gas passage through the intermediate member and the anode member, an axially movable rod-shaed cathode member having an anterior cathode tip and being located generally in the plasma-forming gas passage coaxially in spaced relationship with the anode member operable to maintain a plasma generating arc between the cathode tip and the anode member, priamry gas means including a primary gas inlet for introducing plasma-forming gas into the plasma-forming gas passage rearwardly of the cathode tip, and secondary gas means for introducing plasma-forming gas into the plasma-forming gas passage at a location proximate the anode member, the intermediate member being formed of a plurality of electrically conductive tubular segments and insulating means or spacing the segments, the segments being juxtaposed coaxially and held electrically isolated form each other by the insulating means, and the intermediate member being formed substantially with an absence of additional gas introduction into the plasma-forming gas passage, the method comprising:

• introducing primary plasma-forming gas into the plasma-forming gas passage rearwardly of the cathode tip, introducing secondary plasma-forming gas into the plasma-forming gas passage at a location proximate the anode member, applying an arc voltage between the anode member and the cathode member to generate an arc therebetween, measuring the actual arc voltage and comparing the same with a predetermined arc voltage, and contnually adjusting the axial position of the cathode tip relative to the anode member so as to maintain the actual arc voltage substantially equal to the predetermined arc voltage.