摘要:

The theory and design of a nonmagnetic, multicelled, triode, getter-ion pump capable of attaining pressures of less than3 × 10−11Torr and a pumping speed for air of 1700 liter/sec using a 6-in.-diam orifice is described. A quantitative theory is presented for maximizing the ionizing efficiency of electrons trapped in the electrostatic potential of a cylindrical diode. The experimentally verified theory predicts that for optimum results, electrons must be injected in a well-defined range of angular momenta from an injector whose potential is nearly that of the outer cylindrical electrode. The theory also predicts the optimum axial and radial position for injection. In the new pump, each cell consists of an open cylindrical grid within which is a central anode and two electron injectors. All cells are surrounded by a common cathode which also serves as the pump housing. A new-design, large-area, resistance-heated sublimator with pressure-controlled sublimation rate is located on the axis of the cylindrical cathode. Because the ionizing and gettering functions have been effectively separated it has been possible to optimize each function separately.

ISSN:0022-5355    

DOI:10.1116/1.1492539

出版商:American Vacuum Society    

年代:1967

数据来源: AIP

摘要:

Performance characteristics of a multicelled, electrostatic, triode, getter-ion pump are described, with data on pumping speeds vs pressure for Ar,N2,O2, andH2, starting characteristics, pressure measurement, ultimate pressure, residual gas composition, and operating life. A 6-in.-diam orifice pump has a baffledN2pumping speed of over 1700 liter/sec below5 × 10−7Torr and pumps argon at 25 liter/sec. Pumping speeds higher than those predicted by the titanium sublimation rate are observed forN2,O2, andH2at pressures above10−6Torr. At10−3Torr, theN2speed is higher by a factor of 38. ForN2andO2, the higher than expected pumping speed is attributed to direct interaction of the gas with the sublimator, which operates at a temperature at which the interaction rate is maximal.

ISSN:0022-5355    

DOI:10.1116/1.1492540

出版商:American Vacuum Society    

年代:1967

数据来源: AIP

摘要:

The structure, resistivity, and temperature coefficient of resistance (TCR) of Cr-SiO films with controlled compositions from 0 to 50 at. % SiO have been investigated. Randomly disordered films condense at −196 °C. Higher temperatures introduce varying degrees of order accompanied by disproportionation of SiO and reaction with Cr. This leads to nonhomogeneous structures consisting of amorphousSiO2and Cr–Si phases according to the binary diagram. Metallic particles of α-Cr andCr3Si, with either little or no long-range order or at the most partially crystalline, provide conductivity which decreases with increasingSiO2concentration. The resistance decreases during annealing are proportional to theCr3Siconcentration over a wide composition range. The TCR's of highly disordered films are negative and shift toward positive values upon annealing. Their interpretation requires metallic and thermally activated conduction mechanisms in parallel. The resistivity and TCR changes during annealing are attributed to recrystallization and bridging between islands.

ISSN:0022-5355    

DOI:10.1116/1.1492541

出版商:American Vacuum Society    

年代:1967

数据来源: AIP

摘要:

A process is described for the vacuum deposition of thin films of superconductive niobium for use as electrical ground planes in cryoelectric circuitry. High-purity niobium films are deposited onto glass and aluminum substrates by evaporation from a focused electron-beam-heated source.The deposition process is described in detail, and the influence of substrate temperature on film purities is discussed. A pinhole-free insulation between 1000–3000 Å is formed on the niobium films by anodization, and the surface roughness of the niobium is examined with an electron microscope as a function of oxide thickness. The superconducting properties of the niobium films are described in terms of their critical temperature, lattice parameter, resistance ratio, critical currents of shielded Sn films, and their ability to resist flux trapping.

ISSN:0022-5355    

DOI:10.1116/1.1492542

出版商:American Vacuum Society    

年代:1967

数据来源: AIP

摘要:

A simple approximation is developed for the molecular flow of gas through a cylindrical tube. The pressure distribution along the wall of the tube is derived and is shown to be a good approximation to the short-tube formula of Clausing. Using these results, the problem of measuring the speed of a pump at the end of a tube is examined. If the pressure gauge is located a distance of one tube radius from the pump, then the intrinsic speed is directly measured in the plane of the gauge.To determine the capture coefficient of an open-ended tube whose inner surface has a uniform sticking coefficient, we employ a differential equation which reproduces the Monte Carlo results of Smith and Lewin with an error of less than 5%. For tubes of infinite length the capture coefficient is given byk = 2(σ1/2)/(1 + σ1/2), where σ is the sticking coefficient of the inner-tube surface. We repeat the calculation for tubes which have the exit end closed by a surface of the same sticking factor.

ISSN:0022-5355    

DOI:10.1116/1.1492543

出版商:American Vacuum Society    

年代:1967

数据来源: AIP

摘要:

The kinetics of nitrogen desorption from iron surfaces was studied between 400 ° and 550 °C. The nitrogen desorbed isothermally into the gas phase was made available to the surface by diffusion from within the iron at the desorption temperature. The method of rate measurement involved the collection and volumetric measurement of gas samples at low pressures from specimens only a few square centimeters in area. Specimens were prepared by nitrogenizing zone-refined iron withNH3–H2mixtures having a range ofN2fugacity between 10 and 3000 atm. The surfaces were then cleaned by ion bombardment in a bakeable high-vacuum system.The kinetics of nitrogen desorption from iron was observed to be a surface-controlled process, which showed first-order dependence upon the nitrogen concentration in the iron when conventional ion-bombardment cleaning procedures were employed. However, it was discovered that carbon monoxide is generated in glass systems during ion bombardment and can contaminate the iron surface. When this contamination was reduced, the nitrogen-desorption process was observed to be diffusion controlled at temperatures as low as 400 °C.

ISSN:0022-5355    

DOI:10.1116/1.1492544

出版商:American Vacuum Society    

年代:1967

数据来源: AIP

摘要:

Observations with an electron microscope and with a modified field-emission microscope verify the formation of submicroscopic, whiskerlike projections on the cathode surface, thus lending additional supporting evidence for the association of electrical breakdown with field emission from such sites. Several mechanisms for the formation of whiskers are identified. The predischarge current, with which the initiation of breakdown is associated, is observed to exhibit large fluctuations in the presence of contamination on either or both electrodes, and a tentative explanation is set forth in terms of a special proliferation of small protuberances.

ISSN:0022-5355    

DOI:10.1116/1.1492545

出版商:American Vacuum Society    

年代:1967

数据来源: AIP

摘要:

Mirror reflectances of close to 100% are needed for numerous applications in gas lasers. Since the transmittance of multilayer dielectric films can be reduced to almost zero by increasing the number of layers, the limiting factor is loss introduced by scattering centers. The causes for the formation of the latter are found to be excessive surface roughness or improper cleaning of the substrate in the residual-gas atmosprere of the bell jar and “spitting” of the evaporation source. Techniques for minimizing these effects are described. Mirrors of 6 in. diameter with a reflectance of 99.89% and scattering losses of 0.09% were fabricated forZnS/ThOF2. The reflectance was found to vary with the number of layers displaying a maximum atN = 21.

ISSN:0022-5355    

DOI:10.1116/1.1492546

出版商:American Vacuum Society    

年代:1967

数据来源: AIP

ISSN:0022-5355    

DOI:10.1116/1.1492547

出版商:American Vacuum Society    

年代:1967

数据来源: AIP