High Vacuum Requirements Research Articles

Overview of the current status of solid-gas interface science

The principal methods for establishing the chemical composition, long-range structure, short-range structure and nature of chemical bonding at the S-G interface are reviewed. Electron and ion spectroscopies largely developed over the past two decades have vastly improved our ability to establish the interface chemical composition, and developments over the past 5 years have done much to put the determination of long-range and short-range structures on firm ground. The high vacuum requirements of these techniques limit their applications to interfaces whose stability under evacuation can be reasonably presumed. This is a serious limitation for many solar applications, and new methods of characterization not subject to it are urgently needed. Some possibilities are indicated.

Metallurgical applications of scanning transmission electron microscopy

It is shown that scanning transmission electron microscopy (STEM) has followed two main lines of development, the pure STEM based upon a field emission electron source in which the emphasis is given to high resolution, and a combined system in which STEM is an attachment to a conventional transmission microscope (TEM + STEM). When used in combination with an energy dispersive X-ray spectrometer, the combined TEM + STEM system is shown to be extremely versatile and possibly the more useful for the applied metallurgist. The high vacuum requirements of pure STEM, however, make this system suitable to be used in conjunction with an Auger spectrometer. Examples of the various microanalysis facilities of STEM are given in the article, including micro-diffraction, rocking-beam channelling patterns, qualitative and quantitative X-ray spectroscopy analysis, particle analysis and in situ experimentation. The controversial subject of whether thicker specimens can be studied in STEM compared with conventional TEM is also discussed.

Mirror Mount for Long Wavelength Lasers

A mirror mount is described which features independent rotational and translational motion and satisfies high vacuum requirements.

Microwave and Fast-Acting Valves and Vacuum Couplings for Accelerators

The high vacuum requirements of the Stanford Two-Mile Linear Electron Accelerator plus the radiation produced by electron acceleration have made it necessary to design special vacuum and isolation components. Two of these are special purpose valves capable of operating in a vacuum system at 10-8 torr, and the third is a group of quick-disconnect couplings used for component installation in the beam switchyard area of the accelerator. One valve is an all-metal, 50-megawatt, S-band microwave valve used to isolate an evacuated rectangular waveguide feed system from exposure to air during the replacement of a klystron drive tube for the accelerator. The valve is built with a remeltable indium seal which provides for leak rates on closure below 24 × 10-8 std. cc He/sec. The second valve is a fast-acting unit that was designed for beam axis application within the disk-loaded waveguide accelerator structure. This valve also has an indium seal that is remotely remeltable and has a measured closing time of nine milliseconds. The group of quick-disconnect couplings, which are 6, 10 and 12-inch pipe sizes, are remotely operable, non-elastomer couplings used in the vacuum chamber system of the beam switchyard. The radiation intensity in this area is sufficient to make elastomer seals impractical and to require that replacement of switchyard components be done quickly and remotely. Indium is also used as a reusable seal for these couplings and can be re-formed mechanically to extend seal life.