INFLUENCE OF VACUUM ARC PLASMA EVAPORATOR CATHODE GEOMETRY OF ON VALUE OF ADMISSIBLE ARC DISCHARGE CURRENT

An analysis of main design parameters that determine a level of droplet formation intensity at the generating stage of plasma flow has been given in the paper. The paper considers the most widely used designs of water cooled consumable cathodes. Ti or Ti-Si and Fe-Cr alloys have been taken as a material for cathodes. The following calculated data: average ionic charge Zi for titanium plasma + 1.6; for "titanium-silicon plasma" + 1.2, an electronic discharge 1.6022 . 10(-19) C, an ion velocity v(i) = 2 . 10(4) m/s, an effective volt energy equivalent of heat flow diverted in the cathode U-kappa = 12 V, temperature of erosion cathode surface T-Pi = 550 ; temperature of the cooled cathode surface T-o = 350. have been accepted in order to determine dependence of a maximum admissible arc discharge current on cathode height. The calculations have been carried out for various values of the cathode heights h(kappa) (from 0.02 to 0.05 m). Diameter of a target cathode is equal to 0.08 m for a majority of technological plasma devices, therefore, the area of the erosion surface is S = 0.005 m(2). A thickness selection for a consumable target cathode part in the vacuum arc plasma source has been justified in the paper. The thickness ensures formation of minimum drop phase in the plasma flow during arc cathode material evaporation. It has been shown that a maximum admissible current of an arc discharge is practically equal to the minimum current of stable arcing when thickness of the consumable cathode part is equal to 0.05 m. The admissible discharge current can be rather significant and ensure high productivity during coating process with formation of relatively low amount of droplet phase in the coating at small values of h(kappa).