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Current limitation in an argon discharge
Classified abstracts 1462-l 471 12 1462. Measurement of the neutral vapour density decay following the extinction of a high-current vacuum arc between copper electrodes. GE9 The decay of neutral copper vapour density which follows the extinction of a high current (2-11 kA) vacuum arc between copper electrodes has been measured. The results show that during the period l-8 ms from current zero the vapour density decays at least an order of magnitude slower than expected on the assumption that vapour atoms generated by the arc move freely to the electrode and vacuum chamber surfaces where they condense. The results can be explained, however, if it is assumed that the vapour is produced by evaporation from molten droplets which are emitted from the cathode spots. J E Jenkins et al, JP/i~js D: App/Php, 8 (12), 1975, Ll39-Ll43. I2 1463. Current limitation in an argon discharge. (Canada) Upper and lower limits to the current which can be carried by an electrical discharge have been predicted by recent theories and substantiated by experiments employing Hg vapour. Poor agreement appeared to obtain for other gases, raising uncertainties about the validity of the theoretical model. New experiments have been undertaken with argon for which theoretical-experimental discrepancy was greatest and the new results are found to be in agreement with theory. Possible reasons for the earlier disagreement are considered. P C Stangeby and MA Daoud, CanJP/~yq 53 (15), 1975, 1443-1448. 1464. Time-resolved pinhole camera for observation of nanosecond duration X-W plasma emission. (USA) A vacuum diode with a rear-mounted Pilot-B scintillator has been coupled with a conventional evacuated pinhole camera. The cathode of the diode is fabricated from 2-p thick polycarbonate (Kimfol) with a 200-A aluminium layer on the rear surface. Incident photons with energies above the carbon K edge (284 eV) are highly absorbed in the polycarbonate, but photons with energies below the Kedge are absorbed in the aluminium and produce photoelectrons. This yields a photoelectron sensitivity which is peaked at approximately 275 eV. The photoelectrons are accelerated by a lo-kV cathode potential to an aluminium anode coating on the scintillator, and scintillation photons are observed with an image converter camera. Streak photographs of exploded-wire x-uv radiation taken with this system are presented. D J Johnson et al, Reu Sci Zmfrurn, 46 (9), 1975, 1155-I 157.
Il. Vacuum 20. PUMPING
apparatus
and auxiliaries
SYSTEMS
20 1465. High-vacuum Raman cell for the study of finite particle effects. WW A high-vacuum Raman cell using the backscattering geometry for use in studies of microcrystals, surface effects, and physical and chemical adsorption is described. The circuit 2nd description for a temperature controller are also included. H K B6ckelmann et al, Reu Sci Znstrum, 46 (8), 1975, 1008-l 009.
21. PUMPS
AND
PUMP
FLUIDS
1466. Roots pumps for bigh difference pressures with cooling by gas circulation. (Germany) The principles of the gas-cooled Roots pumps are explained. The characteristics of the pumping speed of one and two stage pumps are given. The pumping speed and the possible temperature limits are calculated thus providing the control of safe operating temperatures at any one pressure. Von H Lang, Wcuum-Tee/z, 24 (5), 1975, 129-132 (in Gernm). 21 1467. The solid state diffusion pump. (GB) The concept of a solid state diffusion pump is discussed. In such a device, ionized atoms are injected into a membrane which separates the pumped region and a higher pressure backing region. The injected ions are not stored indefinitely in this membrane as in ion pump 84
geometry however but are transported across the membrane by diflusion. Diffusion across the membrane is enhanced by a thermal gradient or, more practically, by producing a defect gradient in the membrane by simultaneous ion irradiation from the backing region. G Carter et al, I’UCWWI,25 (7), 1975, 3 15-32 I. 1468. Electrically renewable and controllable oxygen getter. (GB) A brief review of the electric properties of stabilized zirconia indicates that it is an interesting candidate as a basic material for a renewable oxygen getter. Experimental results have confirmed this statement. The material can be electrically reduced simply by passing a dc current through it. Black zirconia thus obtained has an affinity for oxygen close to that of titanium and a high oxygen chemical diffusion coefficient. Under moderate current densities the electrical reduction can be performed in a monophasic region. Thus the material simply reoxidizes by dissolving oxygen, no other compound is formed and the process can be cycled without breaking the sample. Such a getter also presents the advantage of having an electric resistance which sharply varies near saturation. This can provide an easy test for controlling the efficiency of the getter. It was also shown that the electrochemical pump and gauge can be coupled in a very convenient gas circuit to test an oxygen getter. (France) J Fouletier and M Kleitz, ~UCUWI, 25 (7), 1975, 307-314. 1469. Pumps in the early ages of high vacuum technology. (Germany) The history of the development of vacuum pumps in the period of l85@-I966 is briefly given. Von M Dunkel, l’u,&~n-~ccI~, 24 (5), 1975, 133-l 35 (in Gernm)
22. GAUGES
AND
MEASUREMENT
OF LOW
PRESSURES
22 1470. New deflected-beam gauge for pressures below lo-” torr. (USA) Design and performance of a new hot-filament ionization gauge, specially developed for total pressure measurements down to IO-l4 torr, are described. The gauge features an electrostatically deflected ion beam which is directed at the funnel cathode of a small channel electron multiplier (CEM). The spurious signal due to electronic desorption of ions from the anode is extremely small, because these ions are typically of higher initial total energy than those from the residual gas, and may, therefore, be evicted from the high-energy side of the ion beam that is energetically dispersed by the deflecting electric field. The X-ray background corresponds to a pressure in the lo-“’ torr range, and since it can be measured just by inverting the deflector potential, it may easily be zeroed out electronically. Almost none of the secondary particles, released by X-rays or ions from the deflecting electrodes, is counted, because the CEM cathode is operated at high negative potential and because most positive secondary ions are collected at the negative deflecting electrode, due to their small kinetic energy. The gauge’s sensitivity for nitrogen is about 10L7 counts/storr-A, corresponding to 10s/torr for a CEM gain of 10’. It is mounted on a I l3.5-mm metal flange with ceramic feedthroughs and may be baked up to about 3OrC. (Switzerland) D Blechschmidt, J Vat Sci Techno/, 12 (5), 1975, 1072-1078. 22 1471. Application of gas chromatography for direct analysis of gas mixtures in tbe 10m4-10 torr range. (USA) A new technique which combines gas chromatography and uhv techniques is described for the direct analysis of the components of gaseous mixtures whose total pressure lies between lOm4 torr and atmospheric. It therefore covers the gap of total pressure in which both mass spectrometry and traditional gas chromatography are not able to work directly and in a satisfactory way. It has been possible to detect partial pressures down to lO-s-lO-6 torr in a gas at a pressure of 1 torr. Concentrations down to l-10 ppm are, therefore, measured. Due to the limited quantity of the gas required for the analysis, this technique is particularly suitable for the quantitative measurement of impurities present in the filling gas of various devices, even during their operation. Results obtained in a practical case using the technique are reported. (Italy) M Borghi and L Rosai, J Vuc Sci Technol, 12 (5), 1975, 1079-1083.
Il. Vacuum 20. PUMPING
apparatus
and auxiliaries
SYSTEMS
20 1465. High-vacuum Raman cell for the study of finite particle effects. WW A high-vacuum Raman cell using the backscattering geometry for use in studies of microcrystals, surface effects, and physical and chemical adsorption is described. The circuit 2nd description for a temperature controller are also included. H K B6ckelmann et al, Reu Sci Znstrum, 46 (8), 1975, 1008-l 009.
21. PUMPS
AND
PUMP
FLUIDS
1466. Roots pumps for bigh difference pressures with cooling by gas circulation. (Germany) The principles of the gas-cooled Roots pumps are explained. The characteristics of the pumping speed of one and two stage pumps are given. The pumping speed and the possible temperature limits are calculated thus providing the control of safe operating temperatures at any one pressure. Von H Lang, Wcuum-Tee/z, 24 (5), 1975, 129-132 (in Gernm). 21 1467. The solid state diffusion pump. (GB) The concept of a solid state diffusion pump is discussed. In such a device, ionized atoms are injected into a membrane which separates the pumped region and a higher pressure backing region. The injected ions are not stored indefinitely in this membrane as in ion pump 84
geometry however but are transported across the membrane by diflusion. Diffusion across the membrane is enhanced by a thermal gradient or, more practically, by producing a defect gradient in the membrane by simultaneous ion irradiation from the backing region. G Carter et al, I’UCWWI,25 (7), 1975, 3 15-32 I. 1468. Electrically renewable and controllable oxygen getter. (GB) A brief review of the electric properties of stabilized zirconia indicates that it is an interesting candidate as a basic material for a renewable oxygen getter. Experimental results have confirmed this statement. The material can be electrically reduced simply by passing a dc current through it. Black zirconia thus obtained has an affinity for oxygen close to that of titanium and a high oxygen chemical diffusion coefficient. Under moderate current densities the electrical reduction can be performed in a monophasic region. Thus the material simply reoxidizes by dissolving oxygen, no other compound is formed and the process can be cycled without breaking the sample. Such a getter also presents the advantage of having an electric resistance which sharply varies near saturation. This can provide an easy test for controlling the efficiency of the getter. It was also shown that the electrochemical pump and gauge can be coupled in a very convenient gas circuit to test an oxygen getter. (France) J Fouletier and M Kleitz, ~UCUWI, 25 (7), 1975, 307-314. 1469. Pumps in the early ages of high vacuum technology. (Germany) The history of the development of vacuum pumps in the period of l85@-I966 is briefly given. Von M Dunkel, l’u,&~n-~ccI~, 24 (5), 1975, 133-l 35 (in Gernm)
22. GAUGES
AND
MEASUREMENT
OF LOW
PRESSURES
22 1470. New deflected-beam gauge for pressures below lo-” torr. (USA) Design and performance of a new hot-filament ionization gauge, specially developed for total pressure measurements down to IO-l4 torr, are described. The gauge features an electrostatically deflected ion beam which is directed at the funnel cathode of a small channel electron multiplier (CEM). The spurious signal due to electronic desorption of ions from the anode is extremely small, because these ions are typically of higher initial total energy than those from the residual gas, and may, therefore, be evicted from the high-energy side of the ion beam that is energetically dispersed by the deflecting electric field. The X-ray background corresponds to a pressure in the lo-“’ torr range, and since it can be measured just by inverting the deflector potential, it may easily be zeroed out electronically. Almost none of the secondary particles, released by X-rays or ions from the deflecting electrodes, is counted, because the CEM cathode is operated at high negative potential and because most positive secondary ions are collected at the negative deflecting electrode, due to their small kinetic energy. The gauge’s sensitivity for nitrogen is about 10L7 counts/storr-A, corresponding to 10s/torr for a CEM gain of 10’. It is mounted on a I l3.5-mm metal flange with ceramic feedthroughs and may be baked up to about 3OrC. (Switzerland) D Blechschmidt, J Vat Sci Techno/, 12 (5), 1975, 1072-1078. 22 1471. Application of gas chromatography for direct analysis of gas mixtures in tbe 10m4-10 torr range. (USA) A new technique which combines gas chromatography and uhv techniques is described for the direct analysis of the components of gaseous mixtures whose total pressure lies between lOm4 torr and atmospheric. It therefore covers the gap of total pressure in which both mass spectrometry and traditional gas chromatography are not able to work directly and in a satisfactory way. It has been possible to detect partial pressures down to lO-s-lO-6 torr in a gas at a pressure of 1 torr. Concentrations down to l-10 ppm are, therefore, measured. Due to the limited quantity of the gas required for the analysis, this technique is particularly suitable for the quantitative measurement of impurities present in the filling gas of various devices, even during their operation. Results obtained in a practical case using the technique are reported. (Italy) M Borghi and L Rosai, J Vuc Sci Technol, 12 (5), 1975, 1079-1083.