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5.5.3 Ultra High Vacuum

Pressures below 10 $^{\textrm{-8}}$ torr are termed ultra high vacuum. To achieve pressures this low, cyropumps or ion pumps in series with mechanical pumps are used. However, the system must be pumped to low high vacuum pressure before these pumps can be operated, and their pumping speed is comparatively low. Ultra high vacuum also requires other specialized techniques, such as metal-metal connections and high temperature baking of system components to eliminate adsorbed residual gas.

John S. Riley, DSB Scientific Consulting