For arcs with zirconium cathodes in nitrogen, experimental results are presented about changes of material and structure of the cathode, temperature fields, current densities, heat flows, electron work function and erosion rate. The cathode heat regime is described theoretically. I n the experiments, the arc current was 50-200 A.
SummaryThe paper presents results of electrode-surface temperature measurements in the arc-discharge attachment zone. The investigations were carried out on tungsten electrodes in helium atmosphere and on zirconium electrodes in nitrogen atmosphere for currents within the range of 100.. . 200 A.The contribution of plasma radiation to pyrometer readings has been determined. The real temperature of the tungsten electrode surface was measured using the polarised radiation a t the wavelength 1 = 0.65 pm.The energy distribution of arc-spot radiation has been obtained for the spectral range of 0.4. ..1.2 pm. The character of the arc-spot radiation spectrum has been analysed.To estimate the energy balance in an electric-arc chamber, to determine the amount of erosion of the electrodes etc., one should know the electrode-surface temperature (Tb,) in the arc attachment zone. It is one of the arc-discharge determining parameters.The high requirements to the accuracy of electrode temperature measurements are due to the fact that it is related exponentially to the characteristics of such processes as thermoelectron emission, evaporation etc. The value Tbr can vary within a wide range and in the limit achieves the boiling point of the electrode material (for tungsten Thil -N 5900 K). In this case very large temperature gradients may occur either along the attachment surface, or inside the electrode, and the attachment itself may be unstable.The measurements of the electrode-surface temperature can be characterised by the presence of an emitting plasma bulk which screens the surface under study, and by the lack of reliable data on the surface emissive power.In the course of an experiment the state of the surface may change due to evaporation, melting, chemical and recristallisation proceases etc. Besides, vast energy flows supplied from plasma to the electrode surface may affect its emission spectra. The schematic diagram of the electrode surface temperature measurement in the arc attachment zone is given in Fig. 1. The electrode material was tungsten or zirconium. A gas (helium or nitrogen) was supplied from the side of the electrode under study and freely outflowed to the atmosphere throungh the ring electrode. The discharge current in the range of 100.. 300 A.To follow the spectral distribution of the emission energy, we used an IKS-31 monochromator with a diffraction grid and a photoelectric system. I n using the 600 line/mm grid, the linear dispersion amounted to -10 &mm, taking into account the apparatus function. The monochromator was calibrated by using a standard SI-10-300 tungsten lamp. Pyronietric control was performed with the help of a fast photoelectric pyrometer PFM-315 [l]. The scanner diameter on the electrode was -lo-* m, the time resolution The relative contribution of plasma radiation to the readings of the pyrometer was determined, in a stationary mode, from the expression where Eei+pi is the "electrode + plasma" radiation measured along the electrode axis;Epl is the plasma radiation measured a t a dista...
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