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980. Influence of the pre-evacuation cycle on gas atmosphere in a Penning pump system
Classified
abstracts
972-990
pure metal. In order to avoid this contingent, especially the argon which appears on each sublimation, it is proposed that a tungsten wire coated with titanium by vapour plating (pyrolysis) be employed as the sublimation pump filament. Optimum parameters for the deposition process and analyses of the gases released during sublimation, are presented. These filaments may be used for pumping in the pressure range lo-” to lo-la torr. C Biguenet et al, Le Vi&, 23 (133), Jan-Feb 1968, 15-20 (in French). 21 972. Some properties of the PST-1000 type sublimation pump. (France) Construction and performance of the PST-1000 sublimation pump combined with the PZK-100 sputter-ion pump, both of Polish manufacture, are described. The results of measurements of pumping speed for air and nitrogen are presented. Using a plane cathode ion pump considerable argon instability was observed for the pumping of air. Subsequent investigations suggest that argon stability may be achieved using slotted cathodes in the ion pump and ensuring a constant sublimation rate in the titanium pump. 21 R Cyranski, Le Vide, 23 (133), Jan-Feb 1968 21-24 (in French). 973. Sputter-ion pump with high speed for argon. (Germany) Diode sputter ion pumps with argon pumping speeds in excess of 30 per cent of the nitrogen speed are described. The high argon pumping speed and argon stability arise from the use of pill-shaped elements on the cathode arranged so that each anode cell has one pill-shaped element on either side. This arrangement is combined with relatively low magnetic field discharging so that the path of electrons in the anode cell is along the cell axis. Cathode elements are of a composite material based on titanium. The geometry of the cathode-anode arrangement takes into account the cathodic areas, relative to the anode, where noble gas deposition occurs and the sputtering coefficients of the materials employed ensure suppression of these gases once deposited. The improved lifetime of these pumps is attributed to a surface treatment for the backing material to the pill-elements. This treatment produces a uniformly cavitated surface which secures the evaporated deposit in such a way as to prevent subsequent peeling after long term operation. W Blclder, Vukuum-Technik, 17 (3), March 1968, 59-62 (in German). 21 974. Comparative study of diffusion pumps and molecular pumps. (Germany) The principles of operation and performance features of diffusion pumps and molecular pumps are compared and common characteristics are pointed out. It is found possible to regard a diffusion pump as a molecular pump with a gaseous momentum transfer device while the molecular pump could be considered as a diffusion pump in which the working fluid was replaced by a solid. It is concluded that comparison of the pumps alone favours the diffusion pump because of its small size and economy but if operational pumpsets are considered these advantages are offset by the large number of accessories required with diffusion pumps as compared to turbomolecular pumps. W Becker, Vakuum-Technik, 17 (3), March 1968, 62-67 (in German). 21 :16 975. The evolution of methane from barium films. (Italy)” The results of a detailed consideration of the factors contributing to methane formation in vacuum devices containing barium films, indicate that, even with low outgassing rates and small amounts of residual gases prior to getter evaporation, relatively large quantities of methane may be generated. Gases liberated from the stainless steel getter ring react with the barium film to form methane. It is also believed that carbon monoxide, from the getter evaporation reacts to form an agent which may be hydrolysed and/or hydrogenated to form methane. The method of getter evaporation and the nature and quantity of residual and adsorbed gases in the system are also contributing factors to methane formation. In colour television tubes, poorly baked graphite may be a significant source and large quantities of methane may be adsorbed on the system walls. The latter may be desorbed at (USA) room temperature by bombardment by argon atoms. J J Moscony, Nuovo Cimento Suppl, 5 (l), 1967, 7-17. 21 : 16 976. A large-surface non-evaporating getter. (Italy)* Consideration of the performance of the St101 alloy getter when employed in ring shaped containers or deep-drawn discs indicated that substantial parts of the getter were not exploited during operation. This led to the development of the “coated getter”, which consists of a thin metal support to which the getter is strongly bonded in a layer
50 microns thick. A patented fabrication technique allows the strong bonding to be obtained without resort to any chemical binding media. The coated getters are inexpensive and their high efficiency is confirmed by experimental results of operation in a variety of tubes and lamps. B Rind1and E Rabusbt, Nuovo Cimento Suppl, 5 (l), 1967,36-50. 21 : 31 977. Pumping of low-noise travelllng wave tubes with a titanium getter pump. (Italy)* The conditions of cathode operation in travelling-wave tubes demand complete freedom from contamination. Using comparison of noise factors as the criterion, several pumping and activation processes were evaluated. Best results were obtained when a titanium getter pump and Bayard-Alpert gauge, both contained in a separate bulb attached to the tube, were incorporated into the pumping system. The bulb and tube were sealed off at 5 x lo-* torr obtained by a combination of zeolite and mercury diffusion pumps. The titanium was evaporated, the cathode activated and finally pumped by the BayardAlpert gauge. The travelling wave tube was then sealed off at a pressure of about lo-lo torr. In this way, tubes were produced having the lowest noise factors which can be reached and since the cathode temperature could be reduced, a lifetime greater than 10,008 hours could be obtained. (France) C Biguenet, Nuovo Cimento SuppI* 5 (l), 1967, 5&55. 21 978. A non-evaporable getter cartridge for use in UHV systems and in appendage pumps. (Italy)* The results of performance tests on non-evaporable getter cartridges, in which a thin layer of St101 (zirconium-aluminium) alloy is bonded to a thin metallic substrate, are presented. Tests were carried out in an all-metal UHV system pumped by a VacIon pump and a zeolite cryotrap. Gas spectra during the pumping cycle and the baking operation were obtained. Sorption tests for carbon monoxide, nitrogen and hydrogen are also reported. The cartridge getters are recommended for application as appendage pumps in special tubes and the larger cartridge-size may find use in laboratory vacuum systems, particle accelerators and pumping stations for electron tubes. C Pisani and P Della Porta, Nuovo Cimento Suppl, 5 (l), 1967, 261273. 21 : 16 979. Mean adsorption time of oil molecules used in vacuum techniques. (Italy)* The adsorption times and activation energies of desorption were determined for several pump oils, including DC-703 and DC-704, by observing the non-stationary flow of these molecules through a highly evacuated borosilicate tube. The experimental system employed a Hickmann pump and liquid nitrogen traps to obtain a pressure, after outgassing, of 3-5x lO-s torr (nitrogen equivalent). The results permit calculation of the time required for diffusion of oil through the vacuum piping of a system. When considering a clean surface it is assumed that oil molecules impinging on the surface cannot be released. Once an adsorbed laver is formed. adsorption time is given by the Frenkel equation with desorption energy almost equal to the latent heat of vaporization. For oil molecules it was found that adsorption times were much less than lo-‘* sec. (Japan) G Tomlnaga, Nuovo Cimento Suppl, 5 (1). 1967, 274-283. 21 980. Influence of the pre-evacuation cycle on gas atmosphere in a Penning pump system. (Italy)+ It has been shown that the use of a suitably trapped rotary pump for the pre-exhaustion of a Penning pump system leads to easier start-up and a lower partial pressure of neon than if liquid-nitrogen cooled zeolite pumps are used. A zeolite (13X) and two sizes of activated alumina were evaluated as trapping materials for use at ambient temperatures. The activated-alumina showed superior trapping properties and remained effective after considerable use. For both alumina and zeolite it was shown that trapped contaminents are easily driven off by heating and may contaminate the system if activated by heating in situ. L Holland et al, NUOYO Cimento Suppl, 5 (l), 1967, 292-300. 22. GAUGES
22 : 47 Residual gas analysis in ultrahigh vacuum by means of the omegatron. See abstract number 1033. 429
abstracts
972-990
pure metal. In order to avoid this contingent, especially the argon which appears on each sublimation, it is proposed that a tungsten wire coated with titanium by vapour plating (pyrolysis) be employed as the sublimation pump filament. Optimum parameters for the deposition process and analyses of the gases released during sublimation, are presented. These filaments may be used for pumping in the pressure range lo-” to lo-la torr. C Biguenet et al, Le Vi&, 23 (133), Jan-Feb 1968, 15-20 (in French). 21 972. Some properties of the PST-1000 type sublimation pump. (France) Construction and performance of the PST-1000 sublimation pump combined with the PZK-100 sputter-ion pump, both of Polish manufacture, are described. The results of measurements of pumping speed for air and nitrogen are presented. Using a plane cathode ion pump considerable argon instability was observed for the pumping of air. Subsequent investigations suggest that argon stability may be achieved using slotted cathodes in the ion pump and ensuring a constant sublimation rate in the titanium pump. 21 R Cyranski, Le Vide, 23 (133), Jan-Feb 1968 21-24 (in French). 973. Sputter-ion pump with high speed for argon. (Germany) Diode sputter ion pumps with argon pumping speeds in excess of 30 per cent of the nitrogen speed are described. The high argon pumping speed and argon stability arise from the use of pill-shaped elements on the cathode arranged so that each anode cell has one pill-shaped element on either side. This arrangement is combined with relatively low magnetic field discharging so that the path of electrons in the anode cell is along the cell axis. Cathode elements are of a composite material based on titanium. The geometry of the cathode-anode arrangement takes into account the cathodic areas, relative to the anode, where noble gas deposition occurs and the sputtering coefficients of the materials employed ensure suppression of these gases once deposited. The improved lifetime of these pumps is attributed to a surface treatment for the backing material to the pill-elements. This treatment produces a uniformly cavitated surface which secures the evaporated deposit in such a way as to prevent subsequent peeling after long term operation. W Blclder, Vukuum-Technik, 17 (3), March 1968, 59-62 (in German). 21 974. Comparative study of diffusion pumps and molecular pumps. (Germany) The principles of operation and performance features of diffusion pumps and molecular pumps are compared and common characteristics are pointed out. It is found possible to regard a diffusion pump as a molecular pump with a gaseous momentum transfer device while the molecular pump could be considered as a diffusion pump in which the working fluid was replaced by a solid. It is concluded that comparison of the pumps alone favours the diffusion pump because of its small size and economy but if operational pumpsets are considered these advantages are offset by the large number of accessories required with diffusion pumps as compared to turbomolecular pumps. W Becker, Vakuum-Technik, 17 (3), March 1968, 62-67 (in German). 21 :16 975. The evolution of methane from barium films. (Italy)” The results of a detailed consideration of the factors contributing to methane formation in vacuum devices containing barium films, indicate that, even with low outgassing rates and small amounts of residual gases prior to getter evaporation, relatively large quantities of methane may be generated. Gases liberated from the stainless steel getter ring react with the barium film to form methane. It is also believed that carbon monoxide, from the getter evaporation reacts to form an agent which may be hydrolysed and/or hydrogenated to form methane. The method of getter evaporation and the nature and quantity of residual and adsorbed gases in the system are also contributing factors to methane formation. In colour television tubes, poorly baked graphite may be a significant source and large quantities of methane may be adsorbed on the system walls. The latter may be desorbed at (USA) room temperature by bombardment by argon atoms. J J Moscony, Nuovo Cimento Suppl, 5 (l), 1967, 7-17. 21 : 16 976. A large-surface non-evaporating getter. (Italy)* Consideration of the performance of the St101 alloy getter when employed in ring shaped containers or deep-drawn discs indicated that substantial parts of the getter were not exploited during operation. This led to the development of the “coated getter”, which consists of a thin metal support to which the getter is strongly bonded in a layer
50 microns thick. A patented fabrication technique allows the strong bonding to be obtained without resort to any chemical binding media. The coated getters are inexpensive and their high efficiency is confirmed by experimental results of operation in a variety of tubes and lamps. B Rind1and E Rabusbt, Nuovo Cimento Suppl, 5 (l), 1967,36-50. 21 : 31 977. Pumping of low-noise travelllng wave tubes with a titanium getter pump. (Italy)* The conditions of cathode operation in travelling-wave tubes demand complete freedom from contamination. Using comparison of noise factors as the criterion, several pumping and activation processes were evaluated. Best results were obtained when a titanium getter pump and Bayard-Alpert gauge, both contained in a separate bulb attached to the tube, were incorporated into the pumping system. The bulb and tube were sealed off at 5 x lo-* torr obtained by a combination of zeolite and mercury diffusion pumps. The titanium was evaporated, the cathode activated and finally pumped by the BayardAlpert gauge. The travelling wave tube was then sealed off at a pressure of about lo-lo torr. In this way, tubes were produced having the lowest noise factors which can be reached and since the cathode temperature could be reduced, a lifetime greater than 10,008 hours could be obtained. (France) C Biguenet, Nuovo Cimento SuppI* 5 (l), 1967, 5&55. 21 978. A non-evaporable getter cartridge for use in UHV systems and in appendage pumps. (Italy)* The results of performance tests on non-evaporable getter cartridges, in which a thin layer of St101 (zirconium-aluminium) alloy is bonded to a thin metallic substrate, are presented. Tests were carried out in an all-metal UHV system pumped by a VacIon pump and a zeolite cryotrap. Gas spectra during the pumping cycle and the baking operation were obtained. Sorption tests for carbon monoxide, nitrogen and hydrogen are also reported. The cartridge getters are recommended for application as appendage pumps in special tubes and the larger cartridge-size may find use in laboratory vacuum systems, particle accelerators and pumping stations for electron tubes. C Pisani and P Della Porta, Nuovo Cimento Suppl, 5 (l), 1967, 261273. 21 : 16 979. Mean adsorption time of oil molecules used in vacuum techniques. (Italy)* The adsorption times and activation energies of desorption were determined for several pump oils, including DC-703 and DC-704, by observing the non-stationary flow of these molecules through a highly evacuated borosilicate tube. The experimental system employed a Hickmann pump and liquid nitrogen traps to obtain a pressure, after outgassing, of 3-5x lO-s torr (nitrogen equivalent). The results permit calculation of the time required for diffusion of oil through the vacuum piping of a system. When considering a clean surface it is assumed that oil molecules impinging on the surface cannot be released. Once an adsorbed laver is formed. adsorption time is given by the Frenkel equation with desorption energy almost equal to the latent heat of vaporization. For oil molecules it was found that adsorption times were much less than lo-‘* sec. (Japan) G Tomlnaga, Nuovo Cimento Suppl, 5 (1). 1967, 274-283. 21 980. Influence of the pre-evacuation cycle on gas atmosphere in a Penning pump system. (Italy)+ It has been shown that the use of a suitably trapped rotary pump for the pre-exhaustion of a Penning pump system leads to easier start-up and a lower partial pressure of neon than if liquid-nitrogen cooled zeolite pumps are used. A zeolite (13X) and two sizes of activated alumina were evaluated as trapping materials for use at ambient temperatures. The activated-alumina showed superior trapping properties and remained effective after considerable use. For both alumina and zeolite it was shown that trapped contaminents are easily driven off by heating and may contaminate the system if activated by heating in situ. L Holland et al, NUOYO Cimento Suppl, 5 (l), 1967, 292-300. 22. GAUGES
22 : 47 Residual gas analysis in ultrahigh vacuum by means of the omegatron. See abstract number 1033. 429