Acta Technica 65. (1969)

1-2. szám - Bitó, J. F.: The Time and Pressure Dependence of Cathode Properties

2 Acta Technica Academiae Scientiarum Hungaricae; Tomus 6s (1—2). pp. 17—42 (1969) THE TIME AND PRESSURE DEPENDENCE OF CATHODE PROPERTIES J. F. BITÓ CAND. OF TECHN. SC. RESEARCH INSTITUTE FOR ELECTRONICS, BUDAPEST [Manuscript received October 25, 1968] The paper will discuss the principal cathodic and cathode side parameters of mercury vapour — argon arc discharges produced by low-pressure oxide-coated cathodes (together with the relationships between these parameters). Relationships will be established between the cathode spot temperature, cathode fall and cathode emission current under the condi­tions of d.c. and a.c. discharges. I. Introduction The purpose of our investigations was the detailed study of the properties of the low-pressure mercury vapour — argon discharges produced by oxide coated cathodes. On account of the importance of a.c. discharges, this work required the time, pressure, current and type-of-gas dependence of those para­meters to be established. In the following a summary will be presented of the results of studies concerning the time and pressure dependence of the principal cathodic and cathode side parameters. II. Conditions and methods of the tests The measurements were carried out by glass discharge tubes, 1200 mm long by 38 mm diameter. Each of these incorporated electrodes of the same construction (composed of triple tungsten filament coils provided with emitter coating). The tests were made at a discharge current of 430 mA, and at a mer­cury-vapour pressure of 6-10-3 torr (i.e. at an ambient temperature of 25 + 1 °C, using argon as ground gas). Both d.c. and a.c. discharges were pro­duced. No external cathode heating, auxiliary electrode or external magnetic fields were applied. The following methods of testing were used: probe measurement, pyro­métrie and electronic temperature measurement, emission measurement, determination of the cathode space by means of a stroboscope, cathode-spot tests by means of a cathetometer. The current of the discharge tube was limited by means of symmetrically arranged ohmic and inductive external resistors used for d.c. and a.c. discharges, respectively. III. Time dependences The time dependence of the cathode fall is shown in Fig. 1. The horizontal axis represents a half-cycle period (10 msec) which was made to be equal to Acta Technica Academiae Scientiarum Hungaricae 65, 1969

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