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Diffusion pump Diffstak 100

Exhibit no. 179

It is important that the ions have a free run through the mass spectrometer without hitting air molecules. To achieve this, a vacuum must be generated in the instruments.

The vacuum systems of many mass spectrometers consist of a differentially pumped system with a foreline pump establishing a rough vacuum and a high vacuum pump. The high vacuum can be created and maintained by diffusion pumps. Diffusion pumps operate by boiling fluid and forcing the dense vapor stream through central jets angled downward to give a conical curtain of vapor. Gas molecules that randomly enter the pump inlet are pushed toward the boiler and the pump walls by momentum transfer from the more massive fluid molecules. At the air- or water-cooled pump walls, the working fluid condenses and returns under gravity flow downward into the boiler.

The exhibit is Diffstak 100, a compact high-performance water-cooled diffusion pump with 100 mm diameter inlet-flange manufactured by Edwards. The interior jet system consists of a first, second and third-stage jet assembly with fractionating tubes. Above the jet system, there is a detachable first-stage jet-cap. The jet system is clamped together by a central tie-rod. Depending on the working fluid, the pump provides ultimate pressure in 10-8 mbar range. This unit comes from a sector mass spectrometer ZAB-EQ manufactured by VG Analytical LTD. in 1986. The vacuum system of ZAB-EQ encompassed four Diffstak 100 pumps in the analyzer and detector parts, and two Diffstak 160 mm pumps located in the source and focus regions.

Wikipedia: Diffusion pump

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