Conformal plasma cathode for surface hardening of steels

Summary form only given. More than 97% of a bipolar plasma sheath current (and 97% of the power) is carried by the electron component. When an anode workpiece is surrounded by a plasma cathode, the entire anode surface can be illuminated with an electron beam having high current density and high energy. This is particularly useful for heat treatment of steels. Since the plasma cathode can conform to the anode shape, electrons emitted from the plasma cathode can be accelerated across the anode sheath and into the anodic workpiece at normal incidence. If all radii of curvature of the workpiece are larger than the sheath thickness (a few mm), the workpiece surface can be almost uniformly and instantaneously heated. Thermal analysis shows that a single, pulsed, electron beam of energy 10/sup 5/-10/sup 6/ eV and current density 100-1000 A/cm/sup 2/ will heat treat carbon steel surface to a depth of /spl sim/1 mm to achieve high hardness. Several conditions must be achieved to form the desired conformal plasma cathode and to accelerate the desired electron beam. One requirement is that the voltage across the anode sheath must be the major component of the total diode voltage. This can be realized in a fully ionized plasma if the ratio of anode sheath to cathode sheath perveance exceeds 30, and the ratio of plasma containment vessel surface area to workpiece surface area exceeds 10. The diode must operate in a dynamic mode so that the anode sheath grows faster than the cathode sheath. A fully ionized plasma is required.