The vacuum system for the AEI 10m Prototype consists of three tanks with a diameter of 3m and a height of 3.4m, which are connected by 1.5m diameter beam tubes. The tubes are segmented for ease of installation. Overall, the vacuum system encloses about 100m3. It is made of about 22t of stainless steel. It is designed such that it just fits into the existing lab facilities.
There are no gate valves to shut off certain sections of the vacuum system. So whenever the system is vented, the whole system needs to be vented. Attached to the west tube you find a beefy roughing pump. It is a screw pump which pumps 170l/s, starting from atmospheric pressure. Once a pressure of less than a millibar is reached two magnetically levitated turbo-molecular pumps kick into gear. Each of them pumps 2000l/s. The two turbo pumps are backed by a single Scroll pump. With this pump power the system can be pumped to 10-6mbar within 12 hours. After about one week of pumping a pressure of about 10-7mbar can be reached. This will always be dominated by water vapor as the system will not be baked. However, longer pumping will further reduce the residual pressure.
All flanges up to 600mm diameter are sealed with copper gaskets. Flanges bigger than that, i.e. 1000mm at the doors of the tanks, 1500mm at the tube sections, and 3000mm at the lids of the tanks, are sealed with two Viton O-rings each. The gap in between these o-rings is pumped by another Scroll pump. This scheme of differential pumping allows to reach very low residual gas pressure while keeping the cost for the vacuum system at a tolerable level.
The two Scroll pumps, for backing and differential pumping of the big flanges, are located in a pump room separated from the lab. They are set up on a double stack vibration isolator made of two granite plates (ca. 200kg each) and two layers of Sorbothane hemispheres. The pumps themselves also stand on Sorbothane dampers.
The vacuum system is fully installed since Feb. 2009. The remaining leaks at the interconnections of the tube segments were sealed off in May by the insertion of slightly thicker O-rings.