Acta Technica 68. (1970)

1-2. szám - Bitó, J. F.: On the Time Dependence of the Parameters on the Cathode Side

Acta Technica Academiae Scientiarum Hungaricae, Tomus 68 (1—2), pp. 195—197 (1970) ON THE TIME DEPENDENCE OF THE PARAMETERS ON THE CATHODE SIDE J. F. BITÓ CAND. OF TECHN. SC. RESEARCH INSTITUTE FOR ELECTRONICS, BUDAPEST [Manuscript received July 17, 1969] The time dependence of the cathode fall, anode fall and plasma potential of the a.c. oxide cathode discharge was experimentally determined by the author with the aid of an adequate diagnostic system. With the analysis of the time dependence of the cathode spaces he refers to an interesting and characteristic contraction of column in the vicinity of the plasma. I. Experimental conditions, methods Our measurements were carried out with glass discharge tubes of 1200 mm length and 38 mm diameter. Electrodes, made of tungsten triplespiral and having an emission coating, carried on it, were built into these tubes. The examinations were carried out at 430 mA discharge current, by 6 • 10~3 mm Hg mercury vapour pressure — that is to say at 25 + 1°C ambient tempera­ture — with the application of argon ground gas, bringing about an a.c. current discharge of 50 cps frequency. External cathode heating, auxiliary electrodes and external magnetic field were not used. Our experimental methods were the following [1]: probe measurement, pyrométrie and electronic temper­ature measurement, emission measurement, stroboscopic determination of the cathode space-lengths and cathode spot examination by cathetometer. II. Results The probe measurements were carried out at each 10° phase angle in the half period, corresponding to the 180° phase angle, and the cathode fall was determined by extrapolation on the basis of the measured plasma poten­tials. The starting point for the measurement was the moment, when it was characteristic for the peak value of the tube voltage. The half period in our case begins at about 0.55 msec before the closing of the half period. The time dependence curve of the cathode fall follows the formation the tube in time of voltage. In order to manage the time dependence more easily, it is advisable in general to give the average values of the cathode fall, calculat­ed from the momentary values and integrated for the half period. From the plasma potential measurements, carried out at different mo­ments on the probes, protruding into the different points of the positive column aware of the distance between the probes, the time dependence of the potential gradient of the positive column was determined within Acta Technica Academiae Scientiarum IFungarieae 68, 1970

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