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A simple high-sensitivity mass spectrometer
Classified
abstracts
318-327
pressure in the diode pump and (3) pumping speed vs pressure in the triode pump. It was found that the discharge intensity is proportional to pumping speed for pressures below lo* torr for short pumping times. Saturation occurred after pumping times of the order of a day at pressures above lo-’ torr. No significant difference in pumping speed or saturation time was noticed between diode and triode. D Aluert. k?en NASA-CR-75681: R-286: AD-632596. April 1966 (Ill&is &iv *Urbana, Coordinated Scienc; Lab). . _ 21 318. Considerations in the measurement of cryopumping capture coefficients. (USA) A survey is presented of the more important practical and theoretical relations involved in the study of cryopumping. Starting with a rigorous definition of the capture coefficient, the effects of temperature on the measured values are derived. Several practical points in the design of a chamber for cryopumping measurements are given, including cryosurface and gauge placement, calibration effects of outgassing and-impurities, and temperature measurements. J D Haygood and J P Dawson, NASA Accession No N 65-21885, AD 461132,1965,31 pages. _. ‘I 319. Backstreaming from oil diffusion pumps. (USA) The oil diffusion pumps were arranged in five test stations: fractionating and non-fractionating pumps were employed with various types of baffles, and oils. Under optimum conditions an oil deposit equivalent to a monolayer was formed. The amount of this deposit was invariant with long or short runs. The low backstreaming value was obtained only with right angle elbow and chevron baffles. W M Langdon, Rep NASA-CR-74155; ZITRI-C6030-9, 1966 (IIT Research Inst Chicago Illinois). 22. Gauges
22 320. Sensitivity of the Bayard-Alpert ionization gauge and its electrode dimensions. (Poland) After a short discussion of the problem of very low pressures measurements the results are given of systematic investigations of the effect of electrode dimensions on the Bayard-Alpert gauge sensitivity. Measurements were performed continuously using the same type of demountable gauge. The following measurements were made (the relative sensitivities are given in parentheses): the influence of the collector diameter (for 0.008 mm, K=O.l and for 2 mm, K= 1.2); collector length (for L=5 mm, K=0.52, for L=50 mm, K=l); the position of the collector in the grid-shaped anode (with the collector shorter than the anode the sensitivity may vary from 0.3 to 1 according to the collector position); the length of the cathode (varying this length in the ratio 1: 3 the sensitivity changes are not larger than f5 per cent) and the anode-to-cathode distance (practically no influence). The helical and parallel wire electrodes were similarly examined. The influence of the anode end-coverings (which can double the sensitivity) and their potentials (with anode and cathode voltages 220 V and 70 V, respectively, the maximum was at the end-covering voltage 200 V). The gain due to the oscillations of electrons in the anode volume was measured (at lo* torr, a=O.78 to 0.83 due to the dimensions, so G=2.6 to 3.1). J Groszkowski, Archiwum Elektrotech, 15 (2), 1966,459476(in Polish). 22 321. X-ray effect vs ionization gauge geometry. (Poland) After solving the general equations of the collector current due to x-rays emitted by the anode the calculated values are given for this couector electron current (I& as a function of the co&&or dimensions and positions in the system consisting of the grid-shaped cylinder anode with or without end-coverings and the linear collector placed in the anode axis. Conventional Bayard-Alpert gauge with anode current I, has IEC= 1.l x 1O-2 ci,, Bayard-Alpert gauge with end-coverings has IEC= 1.2 x lo-* cJ,, where c is a constant. This x-ray effect can be reduced to 2x 1O-5 cl, in the system consisting of the collector in the anode axis, but out of the anode cylinder, and with theproximal end-coveringmade in the form ofa full plate with an orifice. J Groskowski, Bull Acad PoIon Sci S&rSci Tech, 14 (6)) 1966,551-561 (in English). 22 322. The gain in limit pressure reduction of the Bayard-Alpert gauge due to modulation. (Poland) The lowest pressure that can be measured by a conventional and a modulated Bayard-Alpert gauges was calculated using the same
parameters. In this way the gain in the limit pressure due to the ion current modulation (about 16 for conventional construction) was obtained. The effect of the photo-emission from the collector, the inconstancy of the x-ray effect in MBAG and the modulator rod degassing effect are not taken into account. J Groszkowski, Bull Acad Polon Sci St+ Sci Tech, 14 (6), 1966,563569 (in English). 22 323. Mod&x&ion of the Bayard-Alpert gauge by the addition of a second collector. (USA) A modified inverted ionization gauge is described in which the effective X-ray limit has been substantially reduced. The modification involves the addition of a second collector to the gauge which is biased at a potential below that of the first collector. With the second, the gauge may be operated in the Redhead mode, ie the second collector may be used to modulate ion current using an ac voitage. The modified gauge has an effective x-ray limit at least one and positively two orders of magnitude below that of a standard inverted ionization gauge. Since the gauge is a simple modification of the original Bayard-Alpert design, it can operate with standard power supplies. This gauge is an attractive solution to the problem of reading pressures into the lo-l2 torr range. D Alpert, Rep NASA-CR-75681; R-286; AD-632596, April 1966 (Illinois Univ Urbana, Coordinated Science Lab). 22 324. The suppressor (Schuemann) gauge. (USA) A relatively simple ionization gauge called the photocurrent suppressor gauge for measuring down to lo-l3 torr was developed. The gauge is capable of effectively suppressing the photoelectric current (x-ray current) from the ion collector, thereby considerably extending the range of ionization-type gauges. Its cost in quantity would be little more than a standard inverted gauge while it can measure pressures hundreds of times lower. Because of the compatibility of existing ion gauge supplies, electrometers and measurement techniques the suppressor gauge is believed to offer the most promise for vacuum researchers to develop the know-how to reliably obtain pressures in the 10-l* and 10-l’ torr region. Results indicate that the ion source used in the suppressor gauge could be applied to other instruments, such as mass spectrometers. D Alwrt. Reo NASA-CR-75681: R-286: AD632596. Aoril 1966 Illinois &iv. ‘Urbana, Coordinated Science ‘Lub) . . _ 22 : 30 325. An evaluation of thin film electron sources for use in ionization gauges. (USA) Thin film tri-layer devices were fabricated and evaluated as possible electron sources for mass spectrometers and ionization gauges. The devices consisted of an evaporated metal base, a thin insulating film, and a thin covering metal film. The sandwich materials were usually aluminium-aluminium oxide- gold, although tin oxide was also used. Electron emission currents up to several microamperes were observed, but gave a fractional-hour life. The electron current was noisy. D Apert, Rep NASA-CR-75681; R-286: ADd32596, April 1966 (Illinois Univ Urbana. Coordinated Science Lab). 22 326. A simple high-sensitivity mass spectrometer. (USA) An easily operated high sensitivity mass spectrometer which can be placed on any vacuum station and which uses a magnetic field was investigated theoretically and a model briefly tested. In a mass spectrometer using a magnetic field where a high sensitivity is desired without using an electron multiplier, it is necessary to eliminate fine slits and small cylindrical electron beams. The mass spectrometer described is a partial solution to these problems in that a sheet beam of electrons is used and only one slit for ions is needed. Two forms of the instrument are possible. The more complicated one gives higher resolution while the less complicated one simplifies the electron space charge neutralization problem. A complicated version was built and operated in a magnetic field supplied by a permanent magnet. It had a sensitivity of lo-* amp/torr and a resolution of about IO. The expected sensitivity was 30. Its low sensitivity was attributed to the slit passing only a fraction of the ions through the collector due to poor ion focusing. D Alp&t, Rep NASA-CR-75681: R-286: AD-632596, April 1966 (Illinois Univ Urbana. Coordinated Science Lab). 22 327. Effects of electron-surface interaction in ionization gauges. (US.4 113
abstracts
318-327
pressure in the diode pump and (3) pumping speed vs pressure in the triode pump. It was found that the discharge intensity is proportional to pumping speed for pressures below lo* torr for short pumping times. Saturation occurred after pumping times of the order of a day at pressures above lo-’ torr. No significant difference in pumping speed or saturation time was noticed between diode and triode. D Aluert. k?en NASA-CR-75681: R-286: AD-632596. April 1966 (Ill&is &iv *Urbana, Coordinated Scienc; Lab). . _ 21 318. Considerations in the measurement of cryopumping capture coefficients. (USA) A survey is presented of the more important practical and theoretical relations involved in the study of cryopumping. Starting with a rigorous definition of the capture coefficient, the effects of temperature on the measured values are derived. Several practical points in the design of a chamber for cryopumping measurements are given, including cryosurface and gauge placement, calibration effects of outgassing and-impurities, and temperature measurements. J D Haygood and J P Dawson, NASA Accession No N 65-21885, AD 461132,1965,31 pages. _. ‘I 319. Backstreaming from oil diffusion pumps. (USA) The oil diffusion pumps were arranged in five test stations: fractionating and non-fractionating pumps were employed with various types of baffles, and oils. Under optimum conditions an oil deposit equivalent to a monolayer was formed. The amount of this deposit was invariant with long or short runs. The low backstreaming value was obtained only with right angle elbow and chevron baffles. W M Langdon, Rep NASA-CR-74155; ZITRI-C6030-9, 1966 (IIT Research Inst Chicago Illinois). 22. Gauges
22 320. Sensitivity of the Bayard-Alpert ionization gauge and its electrode dimensions. (Poland) After a short discussion of the problem of very low pressures measurements the results are given of systematic investigations of the effect of electrode dimensions on the Bayard-Alpert gauge sensitivity. Measurements were performed continuously using the same type of demountable gauge. The following measurements were made (the relative sensitivities are given in parentheses): the influence of the collector diameter (for 0.008 mm, K=O.l and for 2 mm, K= 1.2); collector length (for L=5 mm, K=0.52, for L=50 mm, K=l); the position of the collector in the grid-shaped anode (with the collector shorter than the anode the sensitivity may vary from 0.3 to 1 according to the collector position); the length of the cathode (varying this length in the ratio 1: 3 the sensitivity changes are not larger than f5 per cent) and the anode-to-cathode distance (practically no influence). The helical and parallel wire electrodes were similarly examined. The influence of the anode end-coverings (which can double the sensitivity) and their potentials (with anode and cathode voltages 220 V and 70 V, respectively, the maximum was at the end-covering voltage 200 V). The gain due to the oscillations of electrons in the anode volume was measured (at lo* torr, a=O.78 to 0.83 due to the dimensions, so G=2.6 to 3.1). J Groszkowski, Archiwum Elektrotech, 15 (2), 1966,459476(in Polish). 22 321. X-ray effect vs ionization gauge geometry. (Poland) After solving the general equations of the collector current due to x-rays emitted by the anode the calculated values are given for this couector electron current (I& as a function of the co&&or dimensions and positions in the system consisting of the grid-shaped cylinder anode with or without end-coverings and the linear collector placed in the anode axis. Conventional Bayard-Alpert gauge with anode current I, has IEC= 1.l x 1O-2 ci,, Bayard-Alpert gauge with end-coverings has IEC= 1.2 x lo-* cJ,, where c is a constant. This x-ray effect can be reduced to 2x 1O-5 cl, in the system consisting of the collector in the anode axis, but out of the anode cylinder, and with theproximal end-coveringmade in the form ofa full plate with an orifice. J Groskowski, Bull Acad PoIon Sci S&rSci Tech, 14 (6)) 1966,551-561 (in English). 22 322. The gain in limit pressure reduction of the Bayard-Alpert gauge due to modulation. (Poland) The lowest pressure that can be measured by a conventional and a modulated Bayard-Alpert gauges was calculated using the same
parameters. In this way the gain in the limit pressure due to the ion current modulation (about 16 for conventional construction) was obtained. The effect of the photo-emission from the collector, the inconstancy of the x-ray effect in MBAG and the modulator rod degassing effect are not taken into account. J Groszkowski, Bull Acad Polon Sci St+ Sci Tech, 14 (6), 1966,563569 (in English). 22 323. Mod&x&ion of the Bayard-Alpert gauge by the addition of a second collector. (USA) A modified inverted ionization gauge is described in which the effective X-ray limit has been substantially reduced. The modification involves the addition of a second collector to the gauge which is biased at a potential below that of the first collector. With the second, the gauge may be operated in the Redhead mode, ie the second collector may be used to modulate ion current using an ac voitage. The modified gauge has an effective x-ray limit at least one and positively two orders of magnitude below that of a standard inverted ionization gauge. Since the gauge is a simple modification of the original Bayard-Alpert design, it can operate with standard power supplies. This gauge is an attractive solution to the problem of reading pressures into the lo-l2 torr range. D Alpert, Rep NASA-CR-75681; R-286; AD-632596, April 1966 (Illinois Univ Urbana, Coordinated Science Lab). 22 324. The suppressor (Schuemann) gauge. (USA) A relatively simple ionization gauge called the photocurrent suppressor gauge for measuring down to lo-l3 torr was developed. The gauge is capable of effectively suppressing the photoelectric current (x-ray current) from the ion collector, thereby considerably extending the range of ionization-type gauges. Its cost in quantity would be little more than a standard inverted gauge while it can measure pressures hundreds of times lower. Because of the compatibility of existing ion gauge supplies, electrometers and measurement techniques the suppressor gauge is believed to offer the most promise for vacuum researchers to develop the know-how to reliably obtain pressures in the 10-l* and 10-l’ torr region. Results indicate that the ion source used in the suppressor gauge could be applied to other instruments, such as mass spectrometers. D Alwrt. Reo NASA-CR-75681: R-286: AD632596. Aoril 1966 Illinois &iv. ‘Urbana, Coordinated Science ‘Lub) . . _ 22 : 30 325. An evaluation of thin film electron sources for use in ionization gauges. (USA) Thin film tri-layer devices were fabricated and evaluated as possible electron sources for mass spectrometers and ionization gauges. The devices consisted of an evaporated metal base, a thin insulating film, and a thin covering metal film. The sandwich materials were usually aluminium-aluminium oxide- gold, although tin oxide was also used. Electron emission currents up to several microamperes were observed, but gave a fractional-hour life. The electron current was noisy. D Apert, Rep NASA-CR-75681; R-286: ADd32596, April 1966 (Illinois Univ Urbana. Coordinated Science Lab). 22 326. A simple high-sensitivity mass spectrometer. (USA) An easily operated high sensitivity mass spectrometer which can be placed on any vacuum station and which uses a magnetic field was investigated theoretically and a model briefly tested. In a mass spectrometer using a magnetic field where a high sensitivity is desired without using an electron multiplier, it is necessary to eliminate fine slits and small cylindrical electron beams. The mass spectrometer described is a partial solution to these problems in that a sheet beam of electrons is used and only one slit for ions is needed. Two forms of the instrument are possible. The more complicated one gives higher resolution while the less complicated one simplifies the electron space charge neutralization problem. A complicated version was built and operated in a magnetic field supplied by a permanent magnet. It had a sensitivity of lo-* amp/torr and a resolution of about IO. The expected sensitivity was 30. Its low sensitivity was attributed to the slit passing only a fraction of the ions through the collector due to poor ion focusing. D Alp&t, Rep NASA-CR-75681: R-286: AD-632596, April 1966 (Illinois Univ Urbana. Coordinated Science Lab). 22 327. Effects of electron-surface interaction in ionization gauges. (US.4 113