Pumps turbomolecular

Modem UHV chambers are constmcted from stainless steel. The principal seals are metal-on-metal, thus the use of greases is avoided. A combination of pumps is nomially used, including ion pumps, turbomolecular pumps, cryopumps and mechanical (roughing) pumps. The entire system is generally heatable to 500 K. This bakeout for a period of... 

For IBSCA analysis, standard HV or, better, UHV-equipment with turbomolecular pump and a residual gas pressure of less than 10 Pa is necessary. As is apparent from Fig. 4.46, the optical detection system, which consists of transfer optics, a spectrometer, and a lateral-sensitive detector, is often combined with a quadrupole mass spectrometer for analysis of secondary sputtered particles (ions or post-ionized neutrals). 

Such vessels can also be baked at a temperature of several hundred degrees, to drive off any gas adsorbed on metal surfaces. The pumping function of an ion gauge was developed into efficient ionic pumps and turbomolecular pumps , supplemented by low-temperature traps and cryopumps. Finally, sputter-ion pumps, which rely on sorption processes initiated by ionised gas, were introduced. A vacuum of 10 "-10 Torr, true UHV, became routinely accessible in the late 1950s, and surface science could be launched. 

Experiments were carried out in a pulse reactor system based on the TAP-2 reactor described by Cleaves et al. [3]. This consists of a small tubular reactor and a detector housed in a vacujun system pumped by a 1,500 Is" turbomolecular pump to a base pressure of... 

The central transport chamber is an 80-cm-diameter stainless steel vessel, and is pumped by a 1000-1/s turbomolecular pump, which is backed by a small (501/s) turbomolecular pump to increase the compression ratio for hydrogen, and by a 16-m /h rotating-vane pump. UHV is obtained after a bake-out at temperatures above 100°C (measured with thermocouples at the outside surface) of the whole system for about a week. A pressure in the low 10 " -mbar range is then obtained. With a residual gas analyzer (quadrupole mass spectrometer, QMS) the partial pressures of various gases can be measured. During use of the system, the pressure in the central chamber is in the low 10 -mbar range due to loading of samples. Water vapor then is the most abundant species in the chamber. 

FIG. 35. Vertical cross section of the reaction chamber equipped with the mass spectrometer system. Indicated are QMF. the quadmpole mass filter ESA. the electrostatic analyzer CD, the channeltron detector DE, the detector electronics DT, the drift tube lO, the ion optics TMP, the turbomolecular pump PR, the plasma reactor and MN. the matching network. 

Schematic representation of the experimental setup is shown in Fig 1.1. The electrochemical system is coupled on-line to a Quadrupole Mass Spectrometer (Balzers QMS 311 or QMG 112). Volatile substances diffusing through the PTFE membrane enter into a first chamber where a pressure between 10 1 and 10 2 mbar is maintained by means of a turbomolecular pump. In this chamber most of the gases entering in the MS (mainly solvent molecules) are eliminated, a minor part enters in a second chamber where the analyzer is placed. A second turbo molecular pump evacuates this chamber promptly and the pressure can be controlled by changing the aperture between both chambers. Depending on the type of detector used (see below) pressures in the range 10 4-10 5 mbar, (for Faraday Collector, FC), or 10 7-10 9 mbar (for Secondary Electrton Multiplier, SEM) may be established.

Resistance to physical shocks and vibration required careful attention to selection of rugged components and to securing electrical and vacuum systems, wiring, connectors, components, and boards. Chemical ionization (Cl) was used for the first time in a fieldable military detector because of the advent of rugged turbomolecular pumps capable of handling the gas load from the Cl reagent. 

Early in the program, critical components (e.g.,the turbomolecular pump) and circuit boards were tested for their ability to survive neutron and gamma irradiation rates and doses similar to those that would be received from exposure to the detonation of a tactical nuclear device. All components were powered up at the start of the gamma irradiation tests but not during the neutron irradiation tests. Circuit boards were protected by circumvention circuits that powered down critical circuits in 10 to lOOps upon detecting radiation. All components survived the nuclear radiation tests. This unusual performance was noted with positive commendations by the staff at the White Sands Missile Range, where the tests were performed. Tests of the fully integrated CBMS II system, installed in a reconnaissance vehicle, will be conducted in the future. 

The drawback of GALDI is the possible contamination of the ion source with graphite powder that can cause short circuits. The authors have found that the application of thin graphite films and low laser powers minimise the amount of sputtering in the ion source. However, modern commercial spectrometers have compact ion sources that can be easily contaminated, and care should be taken in the use of this methodology. The same is true for turbomolecular pumps if they are located directly below the ion source. 

Fig. 1.17. Internal view of a turbomolecular pump (courtesy of Alcatel).

Resistance bridges sometimes contain a multiplexer to carry out measurement of several thermometers with the same bridge. However, the multiplexing procedure presents several drawbacks (e.g., the temperature readings are not taken at the same time). It is safe, when possible, to use one bridge for each thermometer. The reference frequencies of the bridges must differ for at least a few hertz and of course must not be at the frequency of the power line or motors of the turbomolecular pumps. 

Pumps which transport quantities of gas from the low pressure side to the high pressure side vi/ithout changing the volume of the pumping chamber (Roots pumps, turbomolecular pumps)... 

At the end of the Fifties, it became possible - through a turbine-like design and by modification of the ideas of Gaede - to produce a technically viable pump the socalled Turbomolecular pump . The spaces between the stator and the rotor disks were made in the order of millimeters, so that essentially larger tolerances could be obtained. Thereby, greater security in operation vras achieved. However, a pumping effect of any significance is only attained when the circumferential velocity (at the outside rim) of the... 

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