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4894. Nitrogen sensitivities of a sample of commercial hot cathode ionization gauge tubes
Classified
abstracts
48884897
21 4888. Cyclic pressure fluctuations above rotary pumps and their effects on pumping speed measurements. (USA) The cyclic pressure fluctuations above a positive-displacement rotary vacuum pump are discussed for the case of constant gas flow into a small test volume attached to the pump. It is shown that the average pressure above the pump rises as the test volume is reduced, leading to a corresponding underestimate of the true pumping speed. The effect was apparently discovered almost thirty years ago, but subsequently misinterpreted as a resonance phenomenon. The apparent reduction of pumping speed can range from a few percent or less for medium-sized pumps up to 20-30x for certain extreme cases encountered with large pumps. B R F Kendall, J Vat Sci Technol, 19 (1). 1981. 109-111. 4.
Ll
4889. Effect of hydrogen glow discharge conditioning on Zr/Al getter pumps. (USA) Zr/Al bulk getter pumps are presently being considered for use in the Tokamak Fusion Test Reactor (TFTR) to reduce impurities and limit the recycling of hydrogenic species. It is necessary that these pumps not be adversely affected by the hydrogen glow discharge cleaning (GDC) which is planned as part of the routine TFTR vessel wall conditioning. The GDC procedure involves the use of a dc glow discharge with a 400 V bias voltage. The total fluence of hydrogenic ions given to the affected surfaces during a typical conditioning period is 10” cm -‘. We have investigated the effects of typical GDC runs on a getter-pump module containing 25 g of Zr/Al mounted in a 100 litre test stand. Pumping speed, capacity, and regeneration characteristics have been studied after various exposures to GDC. H F Dylla et al, .I Vat Sci Technol, 18 (3), 1981. 111 l-l 113. 21 4890. Nonevaporable getter for ion beam fusion. (USA) Eddy current effects limit wall thickness of stainless steel chambers in the bending magnet areas of accelerators. Distributed ion pumps are not applicable because of magnetic cycles of these bending magnets. Differential pumping permits applicable inner chamber design but complicates baking and appendage pump mounting. A nonevaporable getter distributed pumping technique (1) is not affected by the magnetic cycle of bending magnets, (2) will provide a minimum of four times the hydrogen speed of appendage ion pumps. (3) will require no power during pumps after strip is activated, (4) will provide the heat source for bakeout, (5) is easily replaceable, and (6) can be purchased, installed, and operated at a generous economic advantage over a completely ion pumped system. J S Moenich, J Vat Sci Techno/, 18 (3), 1981, 1114-l 116. 21 4891. A nonevaporable low temperature activatable getter material. (USA) Nonevaporable getters have been widely used for many years in sealed vacuum or controlled atmosphere devices. They are also finding applications in other fields, where specific characteristics are required and tailor-made getters are requested. in some cases sacrificing speed in favour of lower activation temperatures, or lower operating temperature, while still maintaining an adequate sorption capacity. With these objectives, a decadelong research project was undertaken which involved investigation of Zr-V-Fe alloys. The physico-chemical properties and the gettering characteristics (speed and capacity) of this family of alloys for some main gases usually present in vacuum devices (H,. Co, N,) have therefore been studied in a rangeofactivation temperatures ofless than about 700°C. The equilibrium pressure of Hz on these materials has also been studied as a function ofconcentration and temperature in a range of pressures less than -- 10 Pa. The results obtained, showing the efficiency of this type ofalloy as a getter in a range of activation temperatures of about SOO’C, are also discussed in comparison with some other well-known getter materials. (Italy) C Boffito et al, J Vat Sci Techol. 18 (3). 1981. 1117 1120.
22. GAUGES
AND MEASUREMENT
OF LOW
PRESSURES
22 4892. A simple graphical method of pressure determination in a McLeod gauge. (GB) This paper describes a simple graphical approach for pressure determination using a conventional McLeod gauge. This method also permits a simultaneous detection of the presence of condensable vapours and gases present in the gauge or the system. The pressures thus determined are 210
compared with those obtained by using the variable technique as applied by Podgursky and Davis. (India) J K N Sharma et al. Vacuum. 31 (4/S). 1981. 195-197.
compression
22 4893. Water vapour pressure gauge. (USA 1 An inexpensIve pressure gauge. able to measure the Nz and H,O components within a vacuum system in the pressure range 1 to 400 p IS described and results of tests of the device are reported. D Edwards Jr and D Gillette, J Vat Sci 7ecltnol. 18 (3). 1981, 1023-1025. 22 4894. Nitrogen sensitivities of a sample of commercial hot cathode ionization gauge tubes. (USA) In order to help assess the magnitude of errors that might arise from the use of uncalibrated ionization gauge tubes and help select the best type of tube when accurate measurements are required we have determined the nitrogen sensitivities from 1O-5 to 10m2 Pa for lots of from two to four each of five different types of commercial hot cathode gauge tubes. Included were conventional triodes and B-A structures of four distinct types. Two types with tungsten filaments-the triodes and tabulated B-A structures-were markedly superior to the others with respect to agreement with manufacturer’s sensitivity, linearity. and uniformity of sensitivity within a type. The least satisfactory results were obtained from the nude B-A structures, which showed significant nonlinearities, sensitivities ranging from 70- 1 lo”,, of the manufacturer’s value, and typical 25”,, differences in sensitivity between the two filaments ofa dual-filament structure. K E McCulloh and C R Tilford, J Vat Sci Technol. 18 (3), 1981.994-996. 22 4895. Application of a simple automatic null method for vapour pressure measurements by the torsion-Knudsen effusion-recoil technique. (USA) A description is given for a null method apparatus for continuous determination of vapour pressure by the “Torsion-Knudsen EffusionRecoil” technique. The compensation system can be operated manually or automatically and is based on an industrial core-magnet moving-coil galvanometer with two windings (10 and 4000 R). The significant advantages of the method are: (a) there is constant sensitivity over the entire pressure range of Knudsen effusion conditions; (b) there is negligible mass load of the torsion element (max. 0.5 g); (c)it is possible to switch the integrated damping on or off at any time desired; (d) system oscillations can be initiated by current pulses; and (e) calibration of the torsion element can be done under high vacuum with improved accuracy. Precision of torsion calibration attained is 0.1 “,,. Resolution is limited by the current measurement and is about 0.6-0.9”,, of the picoammeter range. (Austria) Josef Tomiska. Rer Sci 1~7strut17. 52 (5), 1981. 750 -754. 22 48%. Measurement of neutral gas density with ionization gauges in plasma physics research. (USA) The assessment of neutral gas density in the vicinity of a magnetically confined plasma is necessary for the consideration of atomic processes in fusion research experiments. Ionization gauges can be used provided that steps are taken to restrict the influence of the magnetic field on their sensitivity and to effect the differentiation of the true signal from the plasma produced background. In addition, the gauges must have a rather short time constant and a large signal-to-noise ratio. This paper presents an analysis of the features mentioned, based on a careful review of the literature to date. The results achieved by difierent research workers are discussed within the frame of the foregoing analysis. An attempt to correlate the design criteria underlying the operation of ionization gauges used in plasma is presented. (Israel) A Berman, J Vat Sci Techd. 18 (3). 1981. 1017. 1022. 22 4897. Performance of a simplified directional detector for gas molecules. (USA) A simplified directional detector for gas molecules was developed which does not use the collimator, described in a previous article,’ but has bundled capillaries at the entrance of the detector. The detector’s performance with capillaries is analysed and compared with some experimental results. The directivity depends on the pumping speed of the bell jar, as in the case of the collimator, and on the length-to-diameter ratio of the capillary. The directivity of the detector can be increased - 20 times or more than that of the detector with an orifice of the same diameter. Response time of the detector can be reduced by increasing the number of the capillaries. This detector has been applied to the measurement of the
abstracts
48884897
21 4888. Cyclic pressure fluctuations above rotary pumps and their effects on pumping speed measurements. (USA) The cyclic pressure fluctuations above a positive-displacement rotary vacuum pump are discussed for the case of constant gas flow into a small test volume attached to the pump. It is shown that the average pressure above the pump rises as the test volume is reduced, leading to a corresponding underestimate of the true pumping speed. The effect was apparently discovered almost thirty years ago, but subsequently misinterpreted as a resonance phenomenon. The apparent reduction of pumping speed can range from a few percent or less for medium-sized pumps up to 20-30x for certain extreme cases encountered with large pumps. B R F Kendall, J Vat Sci Technol, 19 (1). 1981. 109-111. 4.
Ll
4889. Effect of hydrogen glow discharge conditioning on Zr/Al getter pumps. (USA) Zr/Al bulk getter pumps are presently being considered for use in the Tokamak Fusion Test Reactor (TFTR) to reduce impurities and limit the recycling of hydrogenic species. It is necessary that these pumps not be adversely affected by the hydrogen glow discharge cleaning (GDC) which is planned as part of the routine TFTR vessel wall conditioning. The GDC procedure involves the use of a dc glow discharge with a 400 V bias voltage. The total fluence of hydrogenic ions given to the affected surfaces during a typical conditioning period is 10” cm -‘. We have investigated the effects of typical GDC runs on a getter-pump module containing 25 g of Zr/Al mounted in a 100 litre test stand. Pumping speed, capacity, and regeneration characteristics have been studied after various exposures to GDC. H F Dylla et al, .I Vat Sci Technol, 18 (3), 1981. 111 l-l 113. 21 4890. Nonevaporable getter for ion beam fusion. (USA) Eddy current effects limit wall thickness of stainless steel chambers in the bending magnet areas of accelerators. Distributed ion pumps are not applicable because of magnetic cycles of these bending magnets. Differential pumping permits applicable inner chamber design but complicates baking and appendage pump mounting. A nonevaporable getter distributed pumping technique (1) is not affected by the magnetic cycle of bending magnets, (2) will provide a minimum of four times the hydrogen speed of appendage ion pumps. (3) will require no power during pumps after strip is activated, (4) will provide the heat source for bakeout, (5) is easily replaceable, and (6) can be purchased, installed, and operated at a generous economic advantage over a completely ion pumped system. J S Moenich, J Vat Sci Techno/, 18 (3), 1981, 1114-l 116. 21 4891. A nonevaporable low temperature activatable getter material. (USA) Nonevaporable getters have been widely used for many years in sealed vacuum or controlled atmosphere devices. They are also finding applications in other fields, where specific characteristics are required and tailor-made getters are requested. in some cases sacrificing speed in favour of lower activation temperatures, or lower operating temperature, while still maintaining an adequate sorption capacity. With these objectives, a decadelong research project was undertaken which involved investigation of Zr-V-Fe alloys. The physico-chemical properties and the gettering characteristics (speed and capacity) of this family of alloys for some main gases usually present in vacuum devices (H,. Co, N,) have therefore been studied in a rangeofactivation temperatures ofless than about 700°C. The equilibrium pressure of Hz on these materials has also been studied as a function ofconcentration and temperature in a range of pressures less than -- 10 Pa. The results obtained, showing the efficiency of this type ofalloy as a getter in a range of activation temperatures of about SOO’C, are also discussed in comparison with some other well-known getter materials. (Italy) C Boffito et al, J Vat Sci Techol. 18 (3). 1981. 1117 1120.
22. GAUGES
AND MEASUREMENT
OF LOW
PRESSURES
22 4892. A simple graphical method of pressure determination in a McLeod gauge. (GB) This paper describes a simple graphical approach for pressure determination using a conventional McLeod gauge. This method also permits a simultaneous detection of the presence of condensable vapours and gases present in the gauge or the system. The pressures thus determined are 210
compared with those obtained by using the variable technique as applied by Podgursky and Davis. (India) J K N Sharma et al. Vacuum. 31 (4/S). 1981. 195-197.
compression
22 4893. Water vapour pressure gauge. (USA 1 An inexpensIve pressure gauge. able to measure the Nz and H,O components within a vacuum system in the pressure range 1 to 400 p IS described and results of tests of the device are reported. D Edwards Jr and D Gillette, J Vat Sci 7ecltnol. 18 (3). 1981, 1023-1025. 22 4894. Nitrogen sensitivities of a sample of commercial hot cathode ionization gauge tubes. (USA) In order to help assess the magnitude of errors that might arise from the use of uncalibrated ionization gauge tubes and help select the best type of tube when accurate measurements are required we have determined the nitrogen sensitivities from 1O-5 to 10m2 Pa for lots of from two to four each of five different types of commercial hot cathode gauge tubes. Included were conventional triodes and B-A structures of four distinct types. Two types with tungsten filaments-the triodes and tabulated B-A structures-were markedly superior to the others with respect to agreement with manufacturer’s sensitivity, linearity. and uniformity of sensitivity within a type. The least satisfactory results were obtained from the nude B-A structures, which showed significant nonlinearities, sensitivities ranging from 70- 1 lo”,, of the manufacturer’s value, and typical 25”,, differences in sensitivity between the two filaments ofa dual-filament structure. K E McCulloh and C R Tilford, J Vat Sci Technol. 18 (3), 1981.994-996. 22 4895. Application of a simple automatic null method for vapour pressure measurements by the torsion-Knudsen effusion-recoil technique. (USA) A description is given for a null method apparatus for continuous determination of vapour pressure by the “Torsion-Knudsen EffusionRecoil” technique. The compensation system can be operated manually or automatically and is based on an industrial core-magnet moving-coil galvanometer with two windings (10 and 4000 R). The significant advantages of the method are: (a) there is constant sensitivity over the entire pressure range of Knudsen effusion conditions; (b) there is negligible mass load of the torsion element (max. 0.5 g); (c)it is possible to switch the integrated damping on or off at any time desired; (d) system oscillations can be initiated by current pulses; and (e) calibration of the torsion element can be done under high vacuum with improved accuracy. Precision of torsion calibration attained is 0.1 “,,. Resolution is limited by the current measurement and is about 0.6-0.9”,, of the picoammeter range. (Austria) Josef Tomiska. Rer Sci 1~7strut17. 52 (5), 1981. 750 -754. 22 48%. Measurement of neutral gas density with ionization gauges in plasma physics research. (USA) The assessment of neutral gas density in the vicinity of a magnetically confined plasma is necessary for the consideration of atomic processes in fusion research experiments. Ionization gauges can be used provided that steps are taken to restrict the influence of the magnetic field on their sensitivity and to effect the differentiation of the true signal from the plasma produced background. In addition, the gauges must have a rather short time constant and a large signal-to-noise ratio. This paper presents an analysis of the features mentioned, based on a careful review of the literature to date. The results achieved by difierent research workers are discussed within the frame of the foregoing analysis. An attempt to correlate the design criteria underlying the operation of ionization gauges used in plasma is presented. (Israel) A Berman, J Vat Sci Techd. 18 (3). 1981. 1017. 1022. 22 4897. Performance of a simplified directional detector for gas molecules. (USA) A simplified directional detector for gas molecules was developed which does not use the collimator, described in a previous article,’ but has bundled capillaries at the entrance of the detector. The detector’s performance with capillaries is analysed and compared with some experimental results. The directivity depends on the pumping speed of the bell jar, as in the case of the collimator, and on the length-to-diameter ratio of the capillary. The directivity of the detector can be increased - 20 times or more than that of the detector with an orifice of the same diameter. Response time of the detector can be reduced by increasing the number of the capillaries. This detector has been applied to the measurement of the