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A novel type of low pressure indicator
Classified Abstracts 908--915
385
Vacuum Apparatus and Auxiliaries 20.
Pumping Systems
22. 20
908. Modular vacuum units. (Great Britain) Anon., Electronic Engng., 35, May 1963, 334. 20
909. Methods of constructing vacuum technical equipment from constructional units. (Great Britain) The only components which are at present available commercially for use in vacuum physics are intended for the assembly of vacuum pumps and tubes. It has been realised that actual pieces of equipment also lend themselves to assembly from prefabricated parts. The author describes such components for various types of vacuum chambers, including internal fittings and connexions to measuring instruments, the general assembly following that of a " Meccano " set. (Germany) w.J.s. V. Winkler, Vacuum, 13 (7), July 1963, 259-266.
21.
P u m p s and P u m p Fluids 21 : 16
910. Sorption pumping at high and ultra-high vaeuo.
(Great
Britain) It is demonstrated that the operating range of a liquid nitrogenchilled synthetic zeolite sorption pump can be extended into the high and ultra-high vacuum regions, without sacrificing system cleanliness by pre-evacuating the system prior to cooling the zeolite through a sorption pump of new design. Pressures as low as 5 x 10 -zz tort were produced in a small system by sorption pumping with liquid nitrogen-chilled Linde 13X molecular sieve (a synthetic zeolite), after pre-evacuation of the system by a small oil diffusion pump. The design of this new type of sorption pump, its operating characteristics and its application in ion-getter-pumped vacuum systems are briefly discussed. (U.S.A.) (Author) P. L. Read, Vacuum, 13 (7), July 1963, 271-275. 21 : 31
911. Microwave processing, Britain)
using ion-getter
pumps.
(Great
The construction properties and performance data of various ion-getter pumps using titanium electrodes are described, special attention being called to the advantage of their application to the manufacture of microwave tubes. Thus contamination of the tube is avoided since the pump uses no liquids and the tubes with connected pumps form an easily movable system, enabling the use of different processing stations. An installation of this type consisting of 24 stations which pass through a predesigned programme is described, Leaks of a completely sealed system can be formed with the help of a small ion-getter pump even at pressures below 10 -9 torr. Such a leak detector has proved useful especially for the production of large klystrons. (Swit-
zerland)
w. J. s.
W. A. Stolz, Vacuum, 13 (6), June 1963, 223-227. 21
912. Swing loaded compression rings for non-lubricated reciprocaring compressors. (U.S.A.) The rings are formed in four sections which interlock to form a circle. Each section is spring loaded by four expander plungers to press the ring against the wall and support the piston. As the sections wear, they ride out on each other so that no gap develops. (U.S.A.) w. J. s. Anon., Chem. & Engng. News, 41 (28), 15 July 1963, 56-58.
Gauges
22 913. A novel type of low pressure indicator. (Great Britain) The proposed indicator makes use of the fact that the electron emission of a sensitive surface will fluctuate with the impact of individual ions. If both the surface area and the number of impacts are small and the energy of the ions sufficiently high ( ~ 2 kV), the fluctuations can be recorded on an oscillograph, the frequency of the fluctuatio.ns being a measure of the gas pressure. The gauge proposed by the author has the form of a field emission microscope, the emitting surface being a tungsten point of 2000A. radius. At a pressure of 10-6 torr, the rate of ionic impact is of the order of 300/see. (Great Britain) W . J. S.
L. Jacob, Nature, 198 (4882), 25 May 1963, 774-775. 22
914. A simple omegatron (Italy)
with additional trapping voltages.
An increased resolving power of a simple omegatron in result of reduced alternating h.f. voltage diminishes the ionic efficiency and the sensitivity of the instrument several times in the case of gases featuring a mass of M ~ 26 u.m.a, limiting the scope of analysis and rendering quantitative analysis more difficult. The simple omegatron of novel design incorporating two trapping voltages has been a means of overcoming this difficulty. The omegatron is provided with an additional pair of electrodes to which an additional trapping voltage is applied, so that the trapping field is far better shaped within the area subjected to analysis, than it happens with the Alpert omegatron. A far higher ionic efficiency (some 100 per cent higher) is the outcome, parallel with a very high separating efficiency (z~Mco2=l) making the quantitative analysis of gases, such as C2He, C3Hs and even the isotopic analysis of crypton possible. The characteristics of the omegatron, as well as results of analysis performed on mixtures of gases where the isotopic composition is taken into account are proof that the instrument may be used with good results in quantitative analysis of pressures ranging below 10 -5 torr. (Poland) (Author) B. Masica, 2nd Internal. Symp. residual gases in electron tubes, Milan, (March 1963), Nuovo Cimento (in press). 22 : 23
915. The design and evaluation of a precision omegatron system. (Italy) Omegatrons of simple structure tend to give only qualitative indications of partial pressure and battery operation is inconvenient when applied to continuous analysis. This paper describes in some detail a fully comprehensive system, designed around a precision built omegatron of rather complex design, capable of reliable and repeatable quantitative measurements. To overcome the distortion and consequent loss of performance inherent in most omegatrons, especially in multi-electrode types, a stacked plate structure, using ceramic spacers of special design and quality, is used to mount the complete electrode system. This includes four R.F. guard rings and a double anode electron gun with low temperature lanthanum boride c a t h o d e ; w i t h special jigs precise geometrical alignment of the electron beam axis is established and this is maintained after prolonged baking and outgassing of the electrodes by eddy current heating. To ensure reliable results over long periods of operation the omegatron is driven from a mains operated fully stabilized and protected control unit. Special features include transistor feed back circuits to control the electron beam current to within ~: 1 per cent over the range 1-100tzA. and direct current amplifiers to measure and display the currents to the accelerating
385
Vacuum Apparatus and Auxiliaries 20.
Pumping Systems
22. 20
908. Modular vacuum units. (Great Britain) Anon., Electronic Engng., 35, May 1963, 334. 20
909. Methods of constructing vacuum technical equipment from constructional units. (Great Britain) The only components which are at present available commercially for use in vacuum physics are intended for the assembly of vacuum pumps and tubes. It has been realised that actual pieces of equipment also lend themselves to assembly from prefabricated parts. The author describes such components for various types of vacuum chambers, including internal fittings and connexions to measuring instruments, the general assembly following that of a " Meccano " set. (Germany) w.J.s. V. Winkler, Vacuum, 13 (7), July 1963, 259-266.
21.
P u m p s and P u m p Fluids 21 : 16
910. Sorption pumping at high and ultra-high vaeuo.
(Great
Britain) It is demonstrated that the operating range of a liquid nitrogenchilled synthetic zeolite sorption pump can be extended into the high and ultra-high vacuum regions, without sacrificing system cleanliness by pre-evacuating the system prior to cooling the zeolite through a sorption pump of new design. Pressures as low as 5 x 10 -zz tort were produced in a small system by sorption pumping with liquid nitrogen-chilled Linde 13X molecular sieve (a synthetic zeolite), after pre-evacuation of the system by a small oil diffusion pump. The design of this new type of sorption pump, its operating characteristics and its application in ion-getter-pumped vacuum systems are briefly discussed. (U.S.A.) (Author) P. L. Read, Vacuum, 13 (7), July 1963, 271-275. 21 : 31
911. Microwave processing, Britain)
using ion-getter
pumps.
(Great
The construction properties and performance data of various ion-getter pumps using titanium electrodes are described, special attention being called to the advantage of their application to the manufacture of microwave tubes. Thus contamination of the tube is avoided since the pump uses no liquids and the tubes with connected pumps form an easily movable system, enabling the use of different processing stations. An installation of this type consisting of 24 stations which pass through a predesigned programme is described, Leaks of a completely sealed system can be formed with the help of a small ion-getter pump even at pressures below 10 -9 torr. Such a leak detector has proved useful especially for the production of large klystrons. (Swit-
zerland)
w. J. s.
W. A. Stolz, Vacuum, 13 (6), June 1963, 223-227. 21
912. Swing loaded compression rings for non-lubricated reciprocaring compressors. (U.S.A.) The rings are formed in four sections which interlock to form a circle. Each section is spring loaded by four expander plungers to press the ring against the wall and support the piston. As the sections wear, they ride out on each other so that no gap develops. (U.S.A.) w. J. s. Anon., Chem. & Engng. News, 41 (28), 15 July 1963, 56-58.
Gauges
22 913. A novel type of low pressure indicator. (Great Britain) The proposed indicator makes use of the fact that the electron emission of a sensitive surface will fluctuate with the impact of individual ions. If both the surface area and the number of impacts are small and the energy of the ions sufficiently high ( ~ 2 kV), the fluctuations can be recorded on an oscillograph, the frequency of the fluctuatio.ns being a measure of the gas pressure. The gauge proposed by the author has the form of a field emission microscope, the emitting surface being a tungsten point of 2000A. radius. At a pressure of 10-6 torr, the rate of ionic impact is of the order of 300/see. (Great Britain) W . J. S.
L. Jacob, Nature, 198 (4882), 25 May 1963, 774-775. 22
914. A simple omegatron (Italy)
with additional trapping voltages.
An increased resolving power of a simple omegatron in result of reduced alternating h.f. voltage diminishes the ionic efficiency and the sensitivity of the instrument several times in the case of gases featuring a mass of M ~ 26 u.m.a, limiting the scope of analysis and rendering quantitative analysis more difficult. The simple omegatron of novel design incorporating two trapping voltages has been a means of overcoming this difficulty. The omegatron is provided with an additional pair of electrodes to which an additional trapping voltage is applied, so that the trapping field is far better shaped within the area subjected to analysis, than it happens with the Alpert omegatron. A far higher ionic efficiency (some 100 per cent higher) is the outcome, parallel with a very high separating efficiency (z~Mco2=l) making the quantitative analysis of gases, such as C2He, C3Hs and even the isotopic analysis of crypton possible. The characteristics of the omegatron, as well as results of analysis performed on mixtures of gases where the isotopic composition is taken into account are proof that the instrument may be used with good results in quantitative analysis of pressures ranging below 10 -5 torr. (Poland) (Author) B. Masica, 2nd Internal. Symp. residual gases in electron tubes, Milan, (March 1963), Nuovo Cimento (in press). 22 : 23
915. The design and evaluation of a precision omegatron system. (Italy) Omegatrons of simple structure tend to give only qualitative indications of partial pressure and battery operation is inconvenient when applied to continuous analysis. This paper describes in some detail a fully comprehensive system, designed around a precision built omegatron of rather complex design, capable of reliable and repeatable quantitative measurements. To overcome the distortion and consequent loss of performance inherent in most omegatrons, especially in multi-electrode types, a stacked plate structure, using ceramic spacers of special design and quality, is used to mount the complete electrode system. This includes four R.F. guard rings and a double anode electron gun with low temperature lanthanum boride c a t h o d e ; w i t h special jigs precise geometrical alignment of the electron beam axis is established and this is maintained after prolonged baking and outgassing of the electrodes by eddy current heating. To ensure reliable results over long periods of operation the omegatron is driven from a mains operated fully stabilized and protected control unit. Special features include transistor feed back circuits to control the electron beam current to within ~: 1 per cent over the range 1-100tzA. and direct current amplifiers to measure and display the currents to the accelerating