Pumping system for the ICARUS 600 ton detector

After having analyzed advantages and disadvantages of the possible solutions for the vacuum system for the T600 we estimate in some details the performance a given commercial solution. Pump down times and final vacuum are computed either analytically and with dedicated simulation software. We also estimated the concentration of impurities left in the volume after the cool down and defined some procedures in order to minimize the final contamination of the LAr. Preliminary considerations The design of the pumping system for the T600 has to be based on the following basic considerations. a) The T600 is actually split in two independent volumes of ≈ 300 m each; the two volumes can be evacuated separately in subsequent times using a single pumping system. b) The shape of the basic volume is rather long and narrow and it will contain the readout chambers, which means complicated and long paths for molecules to reach the exit point to the pump; this suggests the use of several pumping points (at least two, if possible 3 or 4) distributed along the structure in order to attain a good and uniform vacuum degree in a reasonable amount of time. c) In order to evacuate and degas the interstices that will be present in the internal detector, molecular regime has to be reached in all parts of the volume; to ensure a vacuum of the order of 10 10 mbar in the small holes and in between the faced flat surfaces (cables, mechanical components of the chambers) a pressure of less than 10 10 mbar has to be set in the gross volume. d) The evacuation time is not, in our case, a critical parameter; we can easily afford one or two weeks of pumping or whatever reasonable amount of time will be required to attain a good outgassing of the internal surfaces. Therefore the pumping speed is not crucial and the evacuation time will be ultimately limited by the time required to degas the surfaces of the internal detector components. Some heating, obtained for example by injecting hot nitrogen in the cooling serpentines or by injecting hot pure Argon in the internal volume, will help to speedup the procedure much more than using faster pumps. e) Due to the large volume to evacuate, the pumping system will have to work for several hours at large pressure; this has to be taken into account when choosing the backing pumps and designing the system layout.