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The LMJ vacuum vessel is a 10 meter-diameter sphere with almost 200 ports, which gives a volume of 600 m3 , 700 m2 of aluminium and 500 meters of viton gaskets.
To ensure vacuum performances allowing a fast recovery of the nominal pressure (10-06 mbar) during operation, the outgassing rate specification was set to a challenging value (10-06 Pa.m/s at 4 hours) for an industrial vacuum vessel of that size.
Early in the manufacturing process, it was decided to carry out an RnD program to qualify the materials used in terms of outgassing properties, to optimize the cleaning procedure, and to simulate the vacuum behaviour of the vessel with a model.
The paper will summarize the results from the first outgassing measurements to the pumpdown curve.
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