Cryogenic pumping

Two vacuum systems are used to provide both the high vacuum needed for the mass spectrometer and the differential pumping required for the interface region. Rotary pumps are used for the interface region. The high vacuum is obtained using diffusion pumps, cryogenic pumps, or turbo pumps. 

Open the thermal switch by pumping away the helium gas from the IVC and start the DR unit. Sometimes one goes on pumping the IVC while temperature decreases. In this case, since also the cold surfaces of DR act as cryogenic pumps, a flux meter (usually present in a leak detector) tells when pumping must be interrupted (at about 1 K). Otherwise, it is safe to close pumping at 4K. 

Figure 11 Inductively coupled plasma mass spectra of (a) thorium demonstrates the propensity for metal oxide formation in the quadrupole ion trap. Cryogenic pumping (b) reduces the residual gases, resulting in dramatically reduced oxide formation. (From Ref. 50.)...

Different vaeuum systems have been applied in combination with API sonrces An one-stage pumping system with a high-efficiency (cryogenic) pump was used in the original Sciex TAGA and API-111 systems. 

Hastie [131] coupled for the first time a quadrupole mass spectrometer with a Knudsen cell. One of the quadrupole mass spectrometer - Knudsen cell systems used at our laboratory is shown in Fig. 4. The system has been developed to study small alkali metal clusters under equilibrium conditions (see Sect. 3.2). Broad-band photoionization by a 1 kW Hg/Xe lamp is used for the first time in Knudsen effusion mass spectrometry to reduce fragmentation. Other quadrupole mass spectrometer - Knudsen cell systems have for example been developed by Hilpert [132, 133], Fraser and Rammensee [134], Plante [135], Ono et al. [136], Kematick et al. [137], and Edwards et al. [138]. Cryogenic pumping is used in the device by Hilpert to reduce mercury background ion intensities for the study of amalgams [132], The instruments described in Refs. 134,135 use a chopper to modulate the molecular beam from the Knudsen cell. Interfering background ion intensities can, thereby, be subtracted. The apparatus developed by the authors of Refs. 137, 138 renders possible the simultaneous application of Knudsen effusion mass spectrometry and the mass-... 

Six different types of pump are used to evacuate a vacuum system. The first and most common is the mechanical displacement pump [226,227]. The second is the vapour stream pump [228]. The third is the modem turbomolecular pump [229]. The fourth type is the chemical getter pump. The fifth is the ion pump and the sixth is the cryogenic pump [230]. In technical coating systems, the first three types of pump are preferred. The development of these pumps is narrowly associated with the names W. Gaede, I. Langmuir, C. Burch, K. Hickman and W. Becker [221,225]. Cryogenic pumps have also been used to evacuate technical coating plants. 

THE APPLICATION OF CRYOGENIC PUMPING IN A HIGH-MASS-FLOW SYSTEM... 

The Application of Cryogenic Pumping in a High-Mass-Flow System... 

This paper deals with a new cooling method using a cryogenic pump. This type of spot-cooling employs the least amount of coolant and provides a means of obtaining close temperature control. 

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