Investigation of low-temperature plasma generator with divergent channel of the output electrode and some applications of this generator

A review is made of experimental and theoretical investigations of processes occurring in low-temperature plasma generators (LTPG) with divergent channel of the output electrode, and the possibilities of utilizing these generators in new plasma technologies are analyzed. Comparison is made of the characteristics of discharge (including the current-voltage characteristic) in a divergent channel and in a cylindrical channel of uniform cross section. The effect of divergent channel of the output electrode and of its expansion ratio on the pattern of physical processes in LTPGs of different designs is studied. Investigations are performed of the distribution of electric current and heat flux density along a channel with a segmented output electrode. The voltaic equivalents of heat fluxes to cathode and anode are determined. The process of “shunting” of discharge is investigated, which causes fluctuations of electric arc-burning voltage. The investigations involving an LTPG with divergent channel reveal that the voltage amplitude in the case of shunting decreases with increasing current strength and, at high currents of argon arc, does not exceed $1$–$2$ V. Results are given of spectral and visual investigations of LTPG. It is demonstrated that, in an LTPG with divergent channel, the plasma temperature in the region of energy input at currents of $300$ A and higher exceeds $30\,000$ K. The significant part is found which is played by vacuum ultraviolet radiation in the process of closing the arc to anode. The mechanisms of erosion of the tungsten cathode tip are investigated, which play an important part in increasing the cathode service life by way of recirculation of tungsten atoms because of their ionization in the discharge gap. Results are given of using an LTPG with divergent channel of the output electrode in plasma technologies of surface hardening, cutting, and hard-facing of metals. The technology of plasma hardening of wheel pairs, adopted by the RZhD (Russian Railroads) Joint-Stock Company, provides for increasing the service life of railroad wheels by a factor of 1.5–2.