摘要:

When we evacuate a vacuum system with a usual cryopump, temperature of vacuum baking is limited to the value lower than that efficient to reduce the ultimate pressure sufficiently. Especially, a cryopump which can be baked at high temperature (∼200 °C) during regeneration has a potential for the production of extreme high vacuum. We have developed a new type of cryopump with Gifford–McMahon refrigerators which can be baked at such high temperature during regeneration. In order to keep the temperature of refrigerator heads below the maximum sustainable temperature 70 °C, the cryopanels are separated from refrigerators and are cooled with helium gas circulating from refrigerators. Using the new cryopump, an aluminum alloy test dome coated with TiN was pumped down to the pressure less than 1×10−10Pa in a few days after 150 °C vacuum bakeout. The low pressure of extreme high vacuum could be kept at least for 25 d. Major constituents of the final residual gas werem/e=2 (H2) andm/e=28 (N2and CO).

ISSN:0734-2101    

DOI:10.1116/1.577445

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

Photon stimulated desorption of neutral species (PSD) is the major dynamic gas load in electron synchrotron light source. In the National Synchrotron Light Source, (NSLS) PSD presented initial machine commissioning difficulty. Sensitivity to surface contamination on PSD has been experienced during an incident of Fomblin Oil contamination.1U10B‐photon stimulated desorption experimental station is constructed to investigate: 1—the degree of the contribution to the photon stimulated desorption (PSD) from primary photon flux and scattered secondary photon flux, 2—the underlying mechanism for photon stimulated desorption, 3—criteria to chose the proper beam tube material for future accelerators such as SXLS, FEL, superconducting super collider (SSC), ALS... . In this report, only photon stimulated desorption of neutral species (PSD) from stainless steel and aluminum is reported.

ISSN:0734-2101    

DOI:10.1116/1.577446

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

Gases that were desorbed from ball bearings were measured in ultrahigh vacuum of about 1×10−10Torr. Test bearings have the following characteristics: (1) No plated parts, (2) Ag or Pb ion plated balls, (3) MoS2sputtered balls, (4) TiN (plasma chemical vapor deposition)+Ag (ion plating) dual‐coated inner and outer rings, and Ag ion plated balls. Two test bearings supported a stainless‐steel rotor in ultrahigh vacuum, and were loaded axially at 98 N. They were driven by magnetic coupling at 140 rpm. Variations in the pressure and the partial pressure of each gas were caused by desorption from the bearings only. From test results, it was found that Ag or Pb ion plated bearings could be used in ultrahigh vacuum. These bearings settled down to a nondesorbing state in a short rotation time. The rotation time was about 11 h for Ag ion plated bearings, and about 17 h for Pb ion plated bearings. H2, CH4, H2O, CO, N2, CO2, and Ar were the main components of the desorbed gases during rotation.

ISSN:0734-2101    

DOI:10.1116/1.577447

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

The equipment was built to measure outgassing during mechanical motion of internal components in ultrahigh vacuum (UHV). Mechanical motion is separated into three fundamental modes, namely tension and compression, impact, and sliding. Gases released during the motion in UHV are monitored by a total‐ and a partial‐pressure gauge. Hydrogen is the major component of outgassing from stainless steel and outgassing increases when strain, displacement, and sliding speed increase. Repeated motion produces the surface of a lower outgassing condition, similar to the repeated baking and air exposure. The outgassing is considered as a result of thermal effect.

ISSN:0734-2101    

DOI:10.1116/1.577448

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

A subcommittee of the American Vacuum Society (AVS) Recommended Practices Committee has conducted a survey of the cleaning procedures practiced by the ultrahigh vacuum industry and government laboratories. Although no two organizations practiced identical procedure, there was sufficient commonality among those canvassed to suggest that there is a sound basic procedure around which many variations have evolved. In the case of chemical cleaning of stainless steel, it is vapor degreasing, alkaline detergent washing and/or acid cleaning, water rinsing, and then heat drying. Various methods of mechanical, chemical, and thermal cleaning of metals and nonmetals practiced by sample organizations are presented with commentary. The Subcommittee recognizes that different situations call for different cleaning procedures. For this reason it aims to disseminate information so that one may formulate his own procedure best suited to his situation, rather than to recommend a single procedure as the best universally.

ISSN:0734-2101    

DOI:10.1116/1.577449

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

The first atomic bomb used uranium isotope 235, which occurs in nature together with uranium‐238, from which it has to be separated. The separation was accomplished in 1944–1945 in a huge ‘‘diffusion’’ plant using microporous tubing as the diffusion medium. The process was such that moist ambient air could not be tolerated in the process chambers. Accordingly, all the equipment had to be ‘‘free’’ of leaks. Equipment of the size used in the diffusion plant had never been tested to such an extreme specification. A number of leak detection devices were tried and proved inadequate. Ultimately, a simplified mass spectrometer based on the Nier 60 in. spectrometer tube was chosen for leak detection. It could easily be set to detect helium which was the choice for ‘‘probe’’ gas. From an original sensitivity such that a flow of 10−6std cm3of helium could be detected, the current unit has been improved so as to detect a flow of 10−10–10−11std cm3. Size of the detector has been reduced by almost an order of magnitude and operation is highly automated.

ISSN:0734-2101    

DOI:10.1116/1.577450

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

With the growing demand for contamination‐free leak detectors, the replacement of the oil‐sealed mechanical pumps has become an important issue. Despite their higher total ultimate pressure (0.010 Torr), the oil‐free pumps retain the pumping speed for helium at pressures less than 1×10−7Torr. This is sufficient in most applications using a turbomolecular pump as the high vacuum pump. Experimental results obtained with a Contra‐Flow leak detector with both mechanical pumps replaced by oil‐free pumps are presented. System stability and helium background levels permit leak rate measurements near 2×10−10atm cc/s.

ISSN:0734-2101    

DOI:10.1116/1.577451

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

The thermal mass flow controller (MFC) is the upstream gas metering device chosen for a majority of vacuum processes. The purpose of this paper is to identify the important physical phenomena and key parameters which govern the performance of MFCs, but which have been previously unmentioned in the literature. Detailed analytical, simulation, and experimental results define the roles of the various heat transfer mechanisms which characterize the behavior of an MFC. The effect of the gas species is of particular, practical concern in view of the wide variety of gases used in processes and the need for higher levels of measurement reliability. The research shows that for some gases the present use of a gas correction factor should be replaced by a gas correction function.

ISSN:0734-2101    

DOI:10.1116/1.577452

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

The first ‘‘dry pumps’’ based on the Roots/claw principle were launched in 1984 and have made a strong contribution to a revolution in two areas of positive‐displacement pumping in the semiconductor industry. These are (a) the clean pumping of systems and load locks and (b) the continuous pumping of processes which generate copious quantities of particulate, condensate or corrosive material as reaction by‐products. These pumps are now moving into their third generation. In this paper, the current state‐of‐the‐art is reviewed, with particular reference to methods of achieving ultraclean pumping and to solutions to applications where ∼100 g/day of particulate (such as aluminium chloride or silica) must be transmitted through the pump with very high reliability. Issues arising from exhaust management of large arrays of pumps, such as those encountered in modern semiconductor fabrication facilities, are also discussed.

ISSN:0734-2101    

DOI:10.1116/1.577453

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

In order to establish a dynamic pumping system for fusion reactors and other advanced vacuum devices, a new type of roughing pump named turbo‐viscous pump has been developed. The construction of the pump features a multistage ceramic (silicon nitride) rotor assembly and an oil‐free driving unit. The rotor assembly has parallel rotor disks, between which project stator disks from the outer casing with rotor‐stator clearances<100 μm, and a shaft with gas turbine blades. Spiral grooves are cut on either side of the rotor or stator disk of each stage, each of them starting near the center (or at the periphery) and ending at the periphery (or near the center). The pump shaft is supported by gas bearings and is driven by gas impulse turbines at ∼25 000 rpm. No lubricating or cooling oil is used. The turbo‐viscous pump works in a wide pressure range from atmospheric pressure to 10−3Pa. The pumping speed and ultimate pressure attained so far are 0.28 m3/min (at inlet pressures between 10−1and 102Pa) and 1×10−3Pa, respectively.

ISSN:0734-2101    

DOI:10.1116/1.577454

出版商:American Vacuum Society    

年代:1991

数据来源: AIP