摘要:

This paper examines the mechanisms of discovery and invention and the role that a professional society such as the American Vacuum Society can play in promoting scientific and technological advancement. It is argued that discoveries are not, in general, the work of one individual, but that they arise from the combination of many different persons and circumstances, and that the Society can play a vital role in bringing such combinations together.

ISSN:0734-2101    

DOI:10.1116/1.572348

出版商:American Vacuum Society    

年代:1983

数据来源: AIP

摘要:

Six photocathode materials were developed during the period from 1930 to 1963 to provide the spectral response and other characteristics needed for such applications as photometry, television, scintillation counters, and night vision devices. The history and the essential properties of these materials are reviewed and it is shown that all the cathodes resulted from lucky accidents and not from the application of scientific insight. The period of empirical innovation came to an end in the late 1960’s when negative electron affinity (NEA) materials became the first photocathodes that were developed on a strictly scientific basis.

ISSN:0734-2101    

DOI:10.1116/1.571898

出版商:American Vacuum Society    

年代:1983

数据来源: AIP

摘要:

‘‘Canadarm’’ is the remote manipulator system (RMS) given by Canada to NASA for installation on the shuttle orbiter. The RMS is to be used for deployment, retrieval, and handling of payloads up to 65 000 lb mass, 15 ft in diameter and 60 ft in length. Controllability, operating constraints, flight environments, safety, reliability, volume, weight, and power allocations were factors which influenced the design. The system uses brushless dc servomotors to drive the six joints and the end effector of the 50 ft arm in a variety of control modes, which provide both manual and automatic control of arm functions. In describing the system, this paper concentrates on the various mechanical devices which are required to operate in the orbital environment and discusses some of the problems encountered during their development. SPAR Aerospace Ltd., under contract to the National Research Council of Canada, designed, developed, manufactured, tested, and delivered the system, which at the time of this writing has been successfully demonstrated on two flights of the orbiter ‘‘Columbia.’’

ISSN:0734-2101    

DOI:10.1116/1.572085

出版商:American Vacuum Society    

年代:1983

数据来源: AIP

摘要:

An ion pump/gage of the cold cathode magnetron‐type has been operated entirely by solar energy. Experiments were carried out continuously for a period of 18 months, at a latitude of 45°, 27′N. The whole apparatus was placed outside the building on the south side and was exposed to the full annual range of climatic conditions and temperatures. The pump was sealed off in a Pyrex 7740 envelope and was self‐pumping and self‐gaging. Operated only from its solar power source, it maintained the vacuum below 10−5Torr at all times, even after a week without any sunshine. The experiment was carried out to evaluate pumping and gaging requirements in an evacuated solar energy collector.

ISSN:0734-2101    

DOI:10.1116/1.572057

出版商:American Vacuum Society    

年代:1983

数据来源: AIP

摘要:

A new ion‐pump element is described which has high pumping speeds for noble gases, excellent hydrogen pumping, low leakage current, and long life. The long term pumping of argon is very stable with this element. Performance is superior in comparison to diode pumps with differential cathodes and in comparison to conventional triode pumps. The experimental results suggest that the geometrical structure of the cathode enhances the production of high energy neutral atoms, the mechanism by which noble gases are pumped. The low leakage current allows accurate pressure measurement to the 10−8Pa range, which is not possible with conventional triode designs. The geometrical structure of the cathode also ensures uniform erosion. Therefore, cathode life will be longer than that of conventional elements. Resistance to deformation caused by pumping of large quantities of hydrogen is high.

ISSN:0734-2101    

DOI:10.1116/1.572059

出版商:American Vacuum Society    

年代:1983

数据来源: AIP

摘要:

Recent calculations of the conductance of a cylindrical pipe in the molecular flow state are presented. They have been performed using the Monte Carlo method which is recognized nowadays to be based on the most significant physical foundations. Previous results obtained with the help of this method did cover a very limited range of the cylinder length to radius ratios (0≤L/R≤5). Our calculations have permitted us to extend this range to a value 20 times larger (0≤L/R≤100). A striking feature of the results obtained, is a discrepancy between our data and these obtained from Clausing’s analytico‐statistical analysis of this problem. It is increasing as a function ofL/R, the difference reaching asymptotically 50% forL/R→100; Clausing’s results being about two times smaller than ours aroundL/R=100. Moreover, it is found that the previously available data obtained by the Monte Carlo method deviate from ours up to about 25% forL/R=5. We demonstrate that this is a consequence of an incorrect method of determining the angle of the emission cosine law for the particles at the entrance of the duct. Finally, we propose a parametrical relation, obtained by the least squares method, that permit the calculation of the value of the conductance of a cylindrical pipe within the range 0≤L/R≤100 and very likely well above this range.

ISSN:0734-2101    

DOI:10.1116/1.572060

出版商:American Vacuum Society    

年代:1983

数据来源: AIP

摘要:

The standard direct method of driving mechanical boosters has a number of drawbacks, and to overcome these the hydrokinetic drive was developed. Direct and hydrokinetic drives are reviewed and their performances compared. The use of synthetic lubricants in mechanical boosters and their effect on performance is discussed. The main disadvantage when using direct or hydrokinetic drive and pumping corrosive or dangerous gases is the possible leakage of the shaft seal required to seal the input drive shaft of the mechanical booster. To overcome this problem while still retaining the advantages of hydrokinetic drive a magnetic drive system has been developed. A mechanical booster provided with magnetic drive is described and details of its performance given. The performance and limitations of the various drive arrangements are compared.

ISSN:0734-2101    

DOI:10.1116/1.572061

出版商:American Vacuum Society    

年代:1983

数据来源: AIP

ISSN:0734-2101    

DOI:10.1116/1.572062

出版商:American Vacuum Society    

年代:1983

数据来源: AIP

摘要:

In order to allow the users of vacuum measurements to assess the reliability of their measurements, the current state of high‐vacuum standards and gauging is reviewed. The discussion includes several types of high‐vacuum primary standards currently in use, an assessment of probable errors for several types of hot filament ion gauges, user‐controlled factors that may serve to increase the errors, and the information available to date on the performance of a commercially available molecular drag gauge. Examples are given of the introduction of additional errors by the improper application of vacuum gauges.

ISSN:0734-2101    

DOI:10.1116/1.572063

出版商:American Vacuum Society    

年代:1983

数据来源: AIP

摘要:

A knowledge of the distribution function for electrons describing stable and unstable trajectories, respectively, and the evaluation of the stable electrons’ mean lifetime deduced from the properties of the ‘‘electrostatic mirror’’ corresponding to the endplates, allow us to perform a theoretical calculation of ionization efficiency for an orbitron device. The ionization efficiency of the device is calculated for various geometrical and electrical parameters using the preceding theoretical considerations. Comparison between experiments and calculations allow us to validate the theoretical model.

ISSN:0734-2101    

DOI:10.1116/1.572064

出版商:American Vacuum Society    

年代:1983

数据来源: AIP