摘要:

The presence of leaks through the stages of a turbomolecular pump affects its actual compression ratio. The measured compression ratios are in many instances much lower than calculated ones if this effect is not considered in the calculation. A theoretical evaluation is done for the effect of the leakage from high pressure stages to the low pressure stages. A simple model is developed to calculate the decrease in the compression ratio caused by leakage. Two cases are studied in detail, referring to a particular design of the pump: (1) the conductance in the region between the envelope of the pump and the spacer rings is much larger than the conductance between two adjacent spacer rings; (2) the conductance between two adjacent spacer rings is much larger than the conductance in the region between the envelope of the pump and the spacer rings. In the latter case, compression ratios might be very close to the maximum (without leakage). Above considerations show a way to improve compression ratios in turbomolecular pumps. Finally an experimental verification has been performed, the calculated configurations have been tested, and the experimental and theoretical results are compared.

ISSN:0734-2101    

DOI:10.1116/1.577412

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

The design of a valve to some degree is dictated by the size of the required connections. But the internal geometry, which establishes the conductance of the valve, should be based on the three‐dimensional examination of overall conductance. Following published Monte Carlo calculations, the internal designs of small right‐angle valves have been optimized by choosing the right combinations of the seat diameter, internal body diameter, and the length of the stroke. Using this approach, in the case of electromechanically operated valves, the expensive bellows (for compensating the force of the sealing spring) can be entirely eliminated. Comparative experimental verification for the optimal design are presented.

ISSN:0734-2101    

DOI:10.1116/1.577413

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

This paper continues the development of the use of personal computers to design vacuum systems by determining the gas flow through the system as a function of the system pressures. Previous papers have presented a compatible set of short‐tube gas‐flow equations for circular tubes for all pressures from atmosphere to high vacuum1and a computer methodology for combining components in a series arrangement to obtained a complete system design.2Some of the problems of parallel pumped systems are discussed in the present paper and a general outline is presented for their computer solution. The additional data on transmission probabilities through short rectangular tubes which was presented at the 1990 National AVS meeting as a part of this paper has been removed and is to be published separately.

ISSN:0734-2101    

DOI:10.1116/1.577414

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

We report H2, CO, and CO2pumping speed measurements on a linear pump using NEG strip St 707 (Saes Getters Inc.) as a function of both adsorbed gases and number of activations. To simulate the conditions of an operating storage ring a gas mixture of 50% H2, 35% CO, and 15% CO2is used in all measurements. Initial measured pumping speeds of>450l m−1 s−1decrease to 200 and 100l m−1 s−1for H2and CO, respectively, after 70 air exposures. A further drop to 50l m−1 s−1for CO occurs at CO loading of 1×10−2Torr l m−1. CO2and CO pumping speeds are about the same. The photon stimulated desorption for both baked and activated strips is an order of magnitude lower than that for stainless steel.

ISSN:0734-2101    

DOI:10.1116/1.577415

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

Taking as the most recent example the vacuum system of the large electron and positron (LEP) storage ring at CERN, general design considerations for accelerator vacuum systems are discussed. The vacuum system for particle accelerators must provide a low residual gas pressure to meet the basic requirement of a long beam lifetime. During operation, the pressure is strongly affected by direct or indirect interactions of the particle beam with the surrounding vacuum envelope and reveals a beam dependent ‘‘dynamic’’ behavior. The various processes of gas desorption call for specific conditioning methods of the vacuum vessel—e.g., conventional baking complemented withinsituconditioning using the beam—for which the provisions must be included during the design and construction phase. The mechanical choices for the vacuum system have to satisfy external constraints and are intimately linked to the major accelerator systems like magnet design and accelerating sections. Modern accelerators have grown to very large linear size, which leads to the practical limitation that their vacuum systems are strongly dominated by the limited conductance of the vacuum duct—a problem that has been overcome by the extensive use of ‘‘distributed’’ or ‘‘linear integrated’’ pumps. Because of the size and the large number of components, low cost per unit length and high reliability are of prime importance.

ISSN:0734-2101    

DOI:10.1116/1.577416

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

Two 52 MHz radio‐frequency (rf) systems, including cavities and control systems, were fabricated and tested at Chalk River Laboratories and subsequently installed in the hadron electron ring accelerator (HERA) proton storage ring at DESY in Hamburg, West Germany. The cavities, with a volume exceeding 1 m3and constructed entirely of aluminum alloy, must achieve the low operating pressures of the HERA proton storage ring and stably provide accelerating voltages from 15 to 150 kV. This paper reviews material choices, fabrication techniques, cleaning, and surface preparation, which have resulted in achievement of these operating goals. Computer simulations identifying potential multipactor areas, suppression of this multipactor, and rf vacuum conditioning processes are discussed.

ISSN:0734-2101    

DOI:10.1116/1.577417

出版商:American Vacuum Society    

年代:1991

数据来源: AIP