Outgassing measurement of an LHC collimator and estimation for the NEG performances

The outgassing rate of the collimators in the Large Hadron Collider (LHC) at CERN has an important role for the life-time of the Non-Evaporable Getter (NEG), and an accurate analysis allows the definition of future activities, like NEG vacuum activation. For these reasons, both, total outgassing rate and gas composition of a secondary collimator have been measured in the laboratory. The outgassing rate decreases by about two orders of magnitude by after bake-out and moreover, repeated bake-out further reduced the outgassing rate. The gas transmission through the NEG coated beam pipes and the resulting pressure distributions near the collimator were also measured in a dedicated setup. It is found that the main gas component after just 2 m of NEG coated beam pipe is CH4 due to the extreme pumping speed of NEG for the other gases. Large amount of outgassing for H2 and carbon related molecules are released when moving the collimator jaws. It is found that the NEG is very effective even in such case with large gas load.

► Outgassing rate and gas composition of a LHC collimator have been measured. ► The main gas component after 2 m of NEG-coated beam pipe is CH4. ► Large amount of outgassing for H2 and C related molecules are released by the jaws movements. ► Life time of the NEG around a collimator in the current setup is estimated to be about 40 years.