Stainless Steel Vacuum Chamber Research Articles

The operation of the ISR facility in relation to the UHV environment

At CERN Geneva, two kilometers of UHV at 10−10 torr is in daily use at the Intersecting Storage Ring (ISR) facility. An appreciable fraction of the stainless steel vacuum chamber, some 200 m in fact, is continuously at 10−11 torr. Nature, we have been told, abhors a vacuum. Nature, in the guise of 28 GeV protons, persists in her abhorrence even when confronted with the brazen face of modern technology. Beams of many amperes of 28 GeV protons circulate for many hours inside the ISR vacuum chambers. A vacuum of 10−10 torr is essential if the protons are to remain unperturbated by collisions with the residual gas molecules. However, when the beam current is allowed to exceed about 5 A, certain regions of the vacuum chamber surface appear to desorb gas molecules and the pressure rises to values in excess of 10−7 torr. Mechaanisms which might give rise to such pressure increases are discussed along with general problems related to the production and maintenance of large scale UHV systems.

A vacuum chamber to study the luminescence emission from liquids and low temperature glasses following electron irradiation

A stainless steel vacuum chamber has been designed for the observation of luminescence emission from liquid or solid samples in the temperature range 80-380K following irradiation by pulses of high energy electrons. The samples may be irradiated in the presence of any gas at pressures between 1 mu Torr and 760 Torr. At low pressures and temperatures radiative heating of the sample becomes important and leads to thermal gradient in the sample. This effect has been investigated and reduced by the use of a cooled 'heat shield'.

Hydrogen and Nitrogen Desorption Phenomena Associated with a Stainless Steel 304 Low Energy Electron Diffraction (LEED) and Molecular Beam Assembly

The rates of hydrogen desorption from the walls of a standard LEED stainless steel vacuum chamber isolated from the ion pump have been measured using an oxygen-free copper orifice of known conductance, which acts as the final focussing slit in a molecular beam assembly, and found unacceptably high for the maintenance of a clean metal single crystal surface. The causes are discussed and the rates of desorption are presented after the stainless steel apparatus had been subjected to vacuum degassing at 850–950 °C in a vacuum furnace at pressures ≤10−5 Torr. Desorption rates are decreased ∼130 times. Rates of desorption of nitrogen from Varian post-acceleration type two and three grid LEED optics screens (P-4 CR 422 phosphor) have been measured. Possible displacement reactions with residual hydrogen, small quantities of which are adsorbed during nitrogen desorption, are discussed. It is concluded that the two processes are independent of each other. Contamination of the single crystal samples with the nitrogen desorbed for the LEED screen is also discussed. Brief reference is made to the adsorption properties of stainless steel 304 with special reference to hydrogen and nitrogen.

Apparatus to Measure Mid-Infrared Spectral Emittance of Cold Powers in a Vacuum

A compact apparatus enclosed in a stainless steel vacuum chamber was used to measure the 8–13 μ emittance of silicate powders under simulated lunar conditions for purposes of compositional analysis. Samples with surface temperatures as low as 180°K could be measured. The sample was contained in the removable lid of a constant temperature bath and its upper surface allowed to radiate into a cavity maintained at liquid nitrogen temperature (77°K). The spectral emittance was computed by matching the observed spectrum with a Planck function at high emittance wavelength intervals. System response was determined with an internal calibrating blackbody maintained at 273°K.

A large dielectric vacuum facility.

I the experimental study and developmental testing of plasma propulsion devices of various types, interference of the vacuum chamber walls with the exhaust plume has proved to be a major limitation on simulation of space operation. This interference may take the form of an artificial constriction of the exhaust plume dimensions, of a recirculation of a portion of the ambient gas in the chamber through the plume, of a participation of the walls in the arc current conduction pattern, or of remote electromagnetic interactions between currents in the plume and induced currents in the walls. The first difficulty clearly relates to chamber size; the second relates to chamber size and to the ambient pressure that can be sustained during thruster operation. The remaining interactions are fostered by the electrical conductivity of the metallic walls of the conventional stainless steel or aluminum vacuum chambers. The desirable facility would thus seem to be a large, dielectric-walled vacuum vessel, capable of low ultimate pressure. Glass or quartz has the most desirable vacuum properties but is essentially unmanageable in the desired sizes. Plastic materials are structurally more convenient, but considerable uncertainty has surrounded their vacuum behavior for the large surface exposures involved in this application. In connection with a program of pulsed plasma acceleration studies described in detail elsewhere, design, construction, and testing of a 50-ft plastic vacuum tank was undertaken, as much to determine its actual vacuum capabilities as to provide a more satisfactory environment for experiments on the ejected plasma. Specifically, this is a vessel of l-in.-thick Plexiglas G~l in the form of a cylinder 3 ft in diameter, 6 ft long, with a hemispherical fixed end and a dish-shaped removable end. Ports are provided for the plasma accelerator at the removable end and for exhaust sampling diagnostics at the fixed end. Each side of the tank also has four large access ports for pumping equipment, gages, diagnostic probes, and photographic flats. Figure 1 shows a sketch of this vessel. The tank was fabricated at a nearby industrial shop§ in the following way. The main body of the vessel was formed by heating a l-in.-thick plane sheet of Plexiglas to about 350°F and bending it over a half-cylinder mandrel, whereon it was

Eddy-Current Phenomena in the Cosmotron

In the Cosmotron magnet, eddy currents in the half-inch laminations cause no serious effects except for a small increase in n value at injection time. This increase needs no correction since it is compensated by the reversed slope of the remanent field. Analyses of eddy-current effects in other metallic components of the Cosmotron are included, for example, in the pole-face windings and in the stainless steel vacuum chamber. Serious shifts in the magnetic median surface result from eddy currents that arise when either inner or outer vertical wall of the vacuum chamber is misaligned.