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The bursting of tubes containing gas discharges
108
Classified Abstracts
18.
Gaseous Electronics
18 256. Current-decay of millisecond duration in thermic valves (the grid-film effect). Great Britain. Pulsed measurements show that the effect consists of a long-time decay nearly completed in 5 msec, and a short-time decay requiring from 10 to 1OOpsec for completion. It is shown to be due to a parallel resistance-capacitance R-C combination in series with the control grid, and values of R from 0 to 800052 and of C from 0.08 to 70pF have been measured. The value of the resistance is inversely proportional both to the temperature of the grid and to the current flowing through it, and it is unaffected by electron bombardment at energies of 400 eV or less. The resistance reduces the initial electronvelocity current and can cause cut-off of the anode current in circuits where the grid potential becomes positive with respect to the cathode. Operation of the valve under normal conditions for 1000 h results in a slight fall in resistance, but under zero current conditions it falls to zero within 48 h. Examination of the grid side rods by electron diffraction indicates the presence of barium and strontium oxides. These are evaporated from the cathode during valve processing, and are deposited as crystallites about 30 8, in size. A strong indication is obtained that the crystallites are oriented mainly at random in a lowresistance film and mainly in preferred orientations in a highresistance film. This is confirmed in patterns obtained from the area of the film causing the current decay in valves with the grid The electrical and physical obserreplaced by a solid collector. vations are shown to be consistent and are compared with the (Author) available information on the oxide-coated cathode. J. Seymour, &it. J. Appl. Phys., 13 (l), Jan. 1962,9-16. 18 257. Estimation of the total emission of a diode. C. S. Bull and R. K. Fitch, Brit. J. AppC. Phys., 13 (4), April 1962, 182-184. 18 258. Low pressure intermittent gas discharges. Australia. The behaviour of a low pressure intermittent gas discharge in air is studied at various values of pressure and as a It is shown function of the parameters of the external circuit. that the ” self-capacity ” of the discharge does not represent a true capacitive effect due to charged particles in the interelectrode gap, but can be explained in terms of the finite width of the discharge pulse. Empirical relations connecting the critical potentials, the pulse width and the circuit capacity are (Author) presented. E. H. Hirsch, hit.
J. Appl. Phys., 13 (6), June 1962, 266-271.
18 259. Skin effect as a factor in the movement of cold-cathode arcs. Great Britain. An arc established between parallel metal electrodes is found to move under the influence of the transverse The magnetic field set up by the arc current in the electrodes. velocity of movement varies with cathode material and characteristic velocity-current curves may be separated into two groups. one comprising the magnetic and the other the non-magnetic metals. It is suggested that the higher velocity of the former group is due to a form of skin effect phenomenon which both radially and circumferentially compresses the current close to the cathode spot and thus gives an enhanced magnetic driving force in the critical region just outside the cathode surface. Experimental results are given to support the proposed mechan(Authors) ism. P. E. Seeker, et al., Brit. J. Appl. Phys., 13 (6), June 1962,282-287. 18 260. Effect of temperature changes on the maintaining voltage of a normal glow discharge. Great Britain. Previously published methods of estimating the
256-264
change in maintaining voltage V, of a normal glow discharge (in which an anode fall is not present) caused by a change in the As cylindrical tube envelope temperature T,n are discussed. geometry was used in each case, exact solutions were not obtained. This paper considers a spherical cathode centrally situated in a spherical envelope for which arrangement an exact solution is possible. Predicted results agree with experimental measurements. Using a simplified model of a glow discharge tube the theory is extended to include the case in which an anode fall is present. Qualitative results show that dV,/dT,, the temperature coefficient, can change from negative to positive under certain conditions due to commencement of formation of an anode fall. This conclusion is confirmed by measurement of the coefficient for an adjustable-gap tube operated in the normal (Author) glow discharge region. J. Smith, Brit. J. Appl. Phys., 13 (B), Aug. 1962, 399-405. 18 261. The bursting of tubes containing gas discharges. Great Britain. During a study of thermal shock effect produced on brittle materials by an intense gas discharge of 20psec duration, breakage of specimens and bursting of tubes sometimes occurred. Observations have been made of the conditions under which these effects occur. Changes in strength and erosion of These observations materials by the discharge were also studied. suggest that breakage is not primarily a thermal shock effect but arises from an impulse generated within the tube. Further experiments on the effect of tube material on specimen breakage and measurements of the impulse produced in a silica tube, as against an aluminia tube, suggest that, for glasses at least, the impulse is caused by a transient high pressure due to evaporation. A semi-quantitative discussion supports this conclusion. (Author) R. A. Dugdale, 508-513.
et al., &it. J. Appl. Phys., 13 (lo), Oct. 1962,
18 : 31 262. The theory and design of an analyser for investigating the electron emission characteristics of surfaces in gases. Great Britain. Ordinary un-outgassed metal surfaces exhibit substantial electron emission (-lo5 electrons per set) under the The influence of electric fields of the order of 103-lo5 V cm-‘. electron emission from a workshop-turned nickel surface under a field of 5 x lo4 V cm-l is about 2 x lo4 e/set in air. Such emission rates can be of considerable importance in the operation switches, contacts, high pressure gas insulation or the initiation of discharges in gases or in vacua. This paper gives an account of the theory and design of an apparatus for measuring the rate of electron emission from given metal surfaces under given (Authors) values of applied electric intensities. F. Llewellyn Jones and D. J. Nicholas, 13 (lo), Oct. 1962, 514-520.
Brit. J. Appl. Phys.,
18 263. Comparison of directional and total intensities of resonance radiation from mercury rare-gas discharge. T. B. Read, &it. J. Appl. Phys., 13 (1 l), Nov. 1962,570. 18 264. Photoelectric emission from cathodes coated with strontium oxide. Great Britain. Observations are reported of the photo-electric emission from strontium oxide cathode coatings which were prepared by the pyrolysis of a strontium carbonate suspension sprayed onto tubular O-nickel cathodes. Each cathode was provided with an insulated tungsten heater and together with an O-nickel anode mounted into experimental tubes having a plane quartz window for illumination of the cathode. The tubes were evacuated and processed in normal manner and the cathode activated by the emission current at about 1150°K. The effective work function (Hensley 1961) was measured at lOOO”K,
Classified Abstracts
18.
Gaseous Electronics
18 256. Current-decay of millisecond duration in thermic valves (the grid-film effect). Great Britain. Pulsed measurements show that the effect consists of a long-time decay nearly completed in 5 msec, and a short-time decay requiring from 10 to 1OOpsec for completion. It is shown to be due to a parallel resistance-capacitance R-C combination in series with the control grid, and values of R from 0 to 800052 and of C from 0.08 to 70pF have been measured. The value of the resistance is inversely proportional both to the temperature of the grid and to the current flowing through it, and it is unaffected by electron bombardment at energies of 400 eV or less. The resistance reduces the initial electronvelocity current and can cause cut-off of the anode current in circuits where the grid potential becomes positive with respect to the cathode. Operation of the valve under normal conditions for 1000 h results in a slight fall in resistance, but under zero current conditions it falls to zero within 48 h. Examination of the grid side rods by electron diffraction indicates the presence of barium and strontium oxides. These are evaporated from the cathode during valve processing, and are deposited as crystallites about 30 8, in size. A strong indication is obtained that the crystallites are oriented mainly at random in a lowresistance film and mainly in preferred orientations in a highresistance film. This is confirmed in patterns obtained from the area of the film causing the current decay in valves with the grid The electrical and physical obserreplaced by a solid collector. vations are shown to be consistent and are compared with the (Author) available information on the oxide-coated cathode. J. Seymour, &it. J. Appl. Phys., 13 (l), Jan. 1962,9-16. 18 257. Estimation of the total emission of a diode. C. S. Bull and R. K. Fitch, Brit. J. AppC. Phys., 13 (4), April 1962, 182-184. 18 258. Low pressure intermittent gas discharges. Australia. The behaviour of a low pressure intermittent gas discharge in air is studied at various values of pressure and as a It is shown function of the parameters of the external circuit. that the ” self-capacity ” of the discharge does not represent a true capacitive effect due to charged particles in the interelectrode gap, but can be explained in terms of the finite width of the discharge pulse. Empirical relations connecting the critical potentials, the pulse width and the circuit capacity are (Author) presented. E. H. Hirsch, hit.
J. Appl. Phys., 13 (6), June 1962, 266-271.
18 259. Skin effect as a factor in the movement of cold-cathode arcs. Great Britain. An arc established between parallel metal electrodes is found to move under the influence of the transverse The magnetic field set up by the arc current in the electrodes. velocity of movement varies with cathode material and characteristic velocity-current curves may be separated into two groups. one comprising the magnetic and the other the non-magnetic metals. It is suggested that the higher velocity of the former group is due to a form of skin effect phenomenon which both radially and circumferentially compresses the current close to the cathode spot and thus gives an enhanced magnetic driving force in the critical region just outside the cathode surface. Experimental results are given to support the proposed mechan(Authors) ism. P. E. Seeker, et al., Brit. J. Appl. Phys., 13 (6), June 1962,282-287. 18 260. Effect of temperature changes on the maintaining voltage of a normal glow discharge. Great Britain. Previously published methods of estimating the
256-264
change in maintaining voltage V, of a normal glow discharge (in which an anode fall is not present) caused by a change in the As cylindrical tube envelope temperature T,n are discussed. geometry was used in each case, exact solutions were not obtained. This paper considers a spherical cathode centrally situated in a spherical envelope for which arrangement an exact solution is possible. Predicted results agree with experimental measurements. Using a simplified model of a glow discharge tube the theory is extended to include the case in which an anode fall is present. Qualitative results show that dV,/dT,, the temperature coefficient, can change from negative to positive under certain conditions due to commencement of formation of an anode fall. This conclusion is confirmed by measurement of the coefficient for an adjustable-gap tube operated in the normal (Author) glow discharge region. J. Smith, Brit. J. Appl. Phys., 13 (B), Aug. 1962, 399-405. 18 261. The bursting of tubes containing gas discharges. Great Britain. During a study of thermal shock effect produced on brittle materials by an intense gas discharge of 20psec duration, breakage of specimens and bursting of tubes sometimes occurred. Observations have been made of the conditions under which these effects occur. Changes in strength and erosion of These observations materials by the discharge were also studied. suggest that breakage is not primarily a thermal shock effect but arises from an impulse generated within the tube. Further experiments on the effect of tube material on specimen breakage and measurements of the impulse produced in a silica tube, as against an aluminia tube, suggest that, for glasses at least, the impulse is caused by a transient high pressure due to evaporation. A semi-quantitative discussion supports this conclusion. (Author) R. A. Dugdale, 508-513.
et al., &it. J. Appl. Phys., 13 (lo), Oct. 1962,
18 : 31 262. The theory and design of an analyser for investigating the electron emission characteristics of surfaces in gases. Great Britain. Ordinary un-outgassed metal surfaces exhibit substantial electron emission (-lo5 electrons per set) under the The influence of electric fields of the order of 103-lo5 V cm-‘. electron emission from a workshop-turned nickel surface under a field of 5 x lo4 V cm-l is about 2 x lo4 e/set in air. Such emission rates can be of considerable importance in the operation switches, contacts, high pressure gas insulation or the initiation of discharges in gases or in vacua. This paper gives an account of the theory and design of an apparatus for measuring the rate of electron emission from given metal surfaces under given (Authors) values of applied electric intensities. F. Llewellyn Jones and D. J. Nicholas, 13 (lo), Oct. 1962, 514-520.
Brit. J. Appl. Phys.,
18 263. Comparison of directional and total intensities of resonance radiation from mercury rare-gas discharge. T. B. Read, &it. J. Appl. Phys., 13 (1 l), Nov. 1962,570. 18 264. Photoelectric emission from cathodes coated with strontium oxide. Great Britain. Observations are reported of the photo-electric emission from strontium oxide cathode coatings which were prepared by the pyrolysis of a strontium carbonate suspension sprayed onto tubular O-nickel cathodes. Each cathode was provided with an insulated tungsten heater and together with an O-nickel anode mounted into experimental tubes having a plane quartz window for illumination of the cathode. The tubes were evacuated and processed in normal manner and the cathode activated by the emission current at about 1150°K. The effective work function (Hensley 1961) was measured at lOOO”K,