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Energy characteristics of ions transmitted by a quadrupole mass filter
Classified abstracts 1301--1309 pulsed voltage smaller and the ion losses due to the angular spread are equal. To generate a longitudinal electric field in the time-offlight tube of the mass spectrometer, it is proposed to make the tube of material with distributed active resistance (surface or volume), for example, the lead-silicate glass used for generation of the longitudinal field in channel electron multipliers. A M Bronshteyn and A E Rafalson, Zh Eksper Teor Fiz, 41 (4), April 1971, 797-799 (in Russ'Jan). 22 1301. Mechanism of operation of ionization gauge head with magnetic field. (Poland) The ionization gauge head with a magnetic field, used for measurement of very low pressures, exhibits high sensitivity. Phenomena taking place in interelectrode space of the head are described. Electrodes of the head form a magnetron system, in which the inner electrode serves as ion collector and the cathode is placed on the end of the cylindrical accelerating electrode, from which ionizing electrons are injected into the system. The tepelling electrode, serving as an electron collector, is placed on the other end of the accelerating electrode. The boundaries of the impact ionization region are determined for super-critical magnetic induction and equations and diagram of the radial distribution of the probability of ionization in the cylindrical system are presented. A logarithmic potential distribution provides the ionizing electrons with sufficient energy for ionization near the inner electrode. The possibility of sensitivity enhancement by utilization of inner reflections is shown. Optimum working conditions are found on experimental heads. Calibration with the aid of a Bayard-Alpert gauge showed a broad range of linearity. With an emission current of 10 8 A, an accelerating electrode voltage of 300 V, and a repelling electrode voltage of 50 V, a sensitivity of 9 × 104 torr ~ was attained with a magnetic field induction of 600 gauss. M Moraw, Pr Nauk lnst Technol Elektron PlYr Ser Stud Mater, No 1, 1970, 5-19 (h~ Polish). 22 : 33 1302. Use of fringing fields in the monopole. (USA) Previous computations of ion trajectories in the monopole mass spectrometer, for ion injection parallel to the instrument axis, have predicted asymmetric peaks with a tail on the low mass side and only 40 per cent ion transmission. This is because an off-axis object cannot be completely focused at the exit from the analyzer. It is shown here that superior focusing at the analyzer exit, leading to symmetrical peaks, 100 per cent ion transmission and, in some conditions, a reduction in the necessary rod-Vee Block spacing, and therefore in rf power, can be obtained by proper use of a fringing field at the monopole entrance. A simple linear entrance ramp, where ion trajectories are mathematically unstable, and which is apparently harmful to the quadrupole mass filter, can be beneficial in the monopole. Examples of computed ion trajectories and peak shapes are given and various entrance ramps are compared. The chance use of an entrance ramp probably explains some of the high performance monopoles that have been constructed. P H Dawson, J Vac Sci Technol, 8 (1), Jan/Feb 1971,263 265. 22 : 33 1303. Operating parameters of a quadrapole in a grounded cylindrical housing. (USA) Quadrupole theory and design are based on the solution of Mathieu's equations, which assume that zero potential, except for the symmetry axes between the electrodes, is infinitely far away. In practice, the quadrupole rods are mounted within a grounded housing not much larger than the electrode structure itself. This study determines the operating parameters and optimum electrode size for a quadrupole with electrodes of circular cross section located within a zeropotential cylindrical surface. It is found that the rod size is only weakly dependent on the location of the external, zero-potential surface and the optimum rod size is r = 1.1468ro for a cylindrical radius of 3.54ro. Although the optimum rod size is only 1.15 per cent smaller than the commonly used value of r=l.16r0, it is found that 43 per cent higher sensitivity at a resolution of 400 (AM measured at halfheight) results from using the optimum radius electrodes. D R Denison, J Vac Sei Technol, 8 (1), Jan~Feb 1971, 266-269. 22 : 33 1304. Energy characteristics of ions transmitted by a quadrupole mass filter. (USA) An idealized model of the quadrupole electric field predicts that ions leaving the exit aperture of a mass filter can have transverse energy as high as 0.7 ~ , and axial energy equal to that of the incoming ions.
A retarding field measurement using a cylindrically symmetric collector has shown that the total energy of transmitted ions is much lower than expected, and has a narrow distribution around the incident ion energy. The energy distribution has been determined for several ions to mass 264 and is found to be mass-dependent. The low energy of emergence and narrow energy distribution indicate possible utility in vacuum applications where a mass-resolved and directed ion beam is required. Improved ion optical design data are available for applications requiring the use of a mass-resolved beam, for instance in detector remote from filter. B E Evans and R W Supple, J Vae Sei Technol, 8 (1), Jan~Feb 1971, 270-272. 22 1305. High-vacuum calibration of a cryogenic quartz crystal--an atmospheric density gauge. (USA) Details of a vacuum calibration of a cryogenically cooled, quartz crystal density gauge are related and the results presented. The gauge (or cryogenic densitometer) design is based on a liquid-helium-cooled quartz water (AT cut 39 ° 45 rain) resonating in its thickness shear mode. Holding the temperature of the quartz crystal below about 15°K permits "cryopumping" of the condensable gases arriving at its surface. Since the frequency of such a crystal shifts monotonically with changes in its mass, the change in frequency can be related directly to the mass density of molecules condensing on the crystal's surface. This mass density may be further related to ambient pressure outside of the gauge by a priori knowledge of the gauge geometry, sensitivity, and other parameters. The sensitivity of the gauge in its present geometry was found to be approximately 1.703 × 10 s Hz/g for molecular nitrogen. The gauge is being prepared for use as a unique atmospheric density probe in the approximate altitude range of 140-180 km. W W Youngblood, J Vac Sci Technol, 8 (1), Jan~Feb 1971,294-298. 22 1306. Development of a miniature quadrupole mass spectrometer. (Germany) The considerations underlying the development of a small, quadrupole residual gas analyzer are discussed, Constructional details of the device and some typical spectra obtained with the gauge are presented. G Rettinghaus and W K Huber, Vakuum-Technik, 20 (3), April 1971, 65-71 (in German).
22 1307. Combined ~- and electron-beam ion source and its cathode properties in the presence of oxygen. (Germany) A device is described in which a polonium-210 source provides approximately 200 millicuries of a-radiation which impinging on a nickel foil gives a beam of secondary electrons suitable as a source of ionization. The sensitivity of the prototype is low, about 10 ~ A/torr but with more efficient ion extraction should afford a sensitivity of the order of 10-6 A/torr. Slight modifications to the circuit arrangement of the ion source will allow application in pressure measurement over a wide range of pressures. F D~iublin, Vakuum-Technik, 20 (3), April 1971, 72-78 (in German). 22 1308. Total pressure measurement of gas-vapour mixtures with a compression gauge. (Germany) The McLeod gauge is normally used for pressure measurements in gas mixtures containing only non-condensable gases. For mixtures with condensable components there does not appear to be any method suitable for routine practical measurements. It is shown that, knowing the composition of the gas mixture and the room temperature vapour pressures of the condensable components, expressions may be derived which permit determination of the pressure using only single reading on a compression gauge. W Weydanz, Vakuum-Technik, 20 (4), May 197 I, 104-110 (in German). 22 1309. Transistorized ionization vacuum gauge circuit. (Japan) A new type of ionization gauge circuit using semiconductor elements is described, which is lighter and smaller than conventional types. Pressure is indicated digitally by an indicating tube driven by an automatic range selector. A series regulating transistor operated by the feedback controlling pulse is used to keep the emission current in the gauge tube constant, and so a low power regulating transistor may be used because of the pulsed filament current. MOS-FET's allow a sensitivity of ion current detection of a few nanoamps which provides for a wide range of pressure indication. T Hayashi et al, J Vac Soc Japan, 14 ( 1), 1971, 18-23 (in Japanese).
563
A retarding field measurement using a cylindrically symmetric collector has shown that the total energy of transmitted ions is much lower than expected, and has a narrow distribution around the incident ion energy. The energy distribution has been determined for several ions to mass 264 and is found to be mass-dependent. The low energy of emergence and narrow energy distribution indicate possible utility in vacuum applications where a mass-resolved and directed ion beam is required. Improved ion optical design data are available for applications requiring the use of a mass-resolved beam, for instance in detector remote from filter. B E Evans and R W Supple, J Vae Sei Technol, 8 (1), Jan~Feb 1971, 270-272. 22 1305. High-vacuum calibration of a cryogenic quartz crystal--an atmospheric density gauge. (USA) Details of a vacuum calibration of a cryogenically cooled, quartz crystal density gauge are related and the results presented. The gauge (or cryogenic densitometer) design is based on a liquid-helium-cooled quartz water (AT cut 39 ° 45 rain) resonating in its thickness shear mode. Holding the temperature of the quartz crystal below about 15°K permits "cryopumping" of the condensable gases arriving at its surface. Since the frequency of such a crystal shifts monotonically with changes in its mass, the change in frequency can be related directly to the mass density of molecules condensing on the crystal's surface. This mass density may be further related to ambient pressure outside of the gauge by a priori knowledge of the gauge geometry, sensitivity, and other parameters. The sensitivity of the gauge in its present geometry was found to be approximately 1.703 × 10 s Hz/g for molecular nitrogen. The gauge is being prepared for use as a unique atmospheric density probe in the approximate altitude range of 140-180 km. W W Youngblood, J Vac Sci Technol, 8 (1), Jan~Feb 1971,294-298. 22 1306. Development of a miniature quadrupole mass spectrometer. (Germany) The considerations underlying the development of a small, quadrupole residual gas analyzer are discussed, Constructional details of the device and some typical spectra obtained with the gauge are presented. G Rettinghaus and W K Huber, Vakuum-Technik, 20 (3), April 1971, 65-71 (in German).
22 1307. Combined ~- and electron-beam ion source and its cathode properties in the presence of oxygen. (Germany) A device is described in which a polonium-210 source provides approximately 200 millicuries of a-radiation which impinging on a nickel foil gives a beam of secondary electrons suitable as a source of ionization. The sensitivity of the prototype is low, about 10 ~ A/torr but with more efficient ion extraction should afford a sensitivity of the order of 10-6 A/torr. Slight modifications to the circuit arrangement of the ion source will allow application in pressure measurement over a wide range of pressures. F D~iublin, Vakuum-Technik, 20 (3), April 1971, 72-78 (in German). 22 1308. Total pressure measurement of gas-vapour mixtures with a compression gauge. (Germany) The McLeod gauge is normally used for pressure measurements in gas mixtures containing only non-condensable gases. For mixtures with condensable components there does not appear to be any method suitable for routine practical measurements. It is shown that, knowing the composition of the gas mixture and the room temperature vapour pressures of the condensable components, expressions may be derived which permit determination of the pressure using only single reading on a compression gauge. W Weydanz, Vakuum-Technik, 20 (4), May 197 I, 104-110 (in German). 22 1309. Transistorized ionization vacuum gauge circuit. (Japan) A new type of ionization gauge circuit using semiconductor elements is described, which is lighter and smaller than conventional types. Pressure is indicated digitally by an indicating tube driven by an automatic range selector. A series regulating transistor operated by the feedback controlling pulse is used to keep the emission current in the gauge tube constant, and so a low power regulating transistor may be used because of the pulsed filament current. MOS-FET's allow a sensitivity of ion current detection of a few nanoamps which provides for a wide range of pressure indication. T Hayashi et al, J Vac Soc Japan, 14 ( 1), 1971, 18-23 (in Japanese).
563