14 February 2008VELO NikhefEddy Jans 0 Cooling and warm-up of the VELO under neon atmosphere conditions results (Jan 28  30) implications

14 February 2008VELO NikhefEddy Jans 1 Warm cool tests with the backup cooler to investigate the possibility to operate the VELO and PU-detectors, while LHCb beam pipe and VELO are under a neon atmosphere of ≈860 mbar. How do AP (=p beam ) and DP (=p beam - p det ) behave ??? Recently temperature variations in the pit have generated variations in DP of the order of 3 mbar in 5 hours. Baseline: Vacuum PLC and active neon gas injection system (GIS) guarantee that DP stays within range, i.e. (-5,+2) mbar. However, present GIS is not designed for continuous operation. Data taken on January 30, 2008

14 February 2008VELO NikhefEddy Jans 2 Cooldown to 10 o C DP [mbar] Baseplate heating ON  DP=4 mbar BPH OFF  DP=3 mbar BPH ON T [ o C]

14 February 2008VELO NikhefEddy Jans 3 Warmup from 10 o C T [ o C] DP [mbar]

14 February 2008VELO NikhefEddy Jans 4 Via movement of the detector halves it is possible to manipulate mbar 1 mm/half corresponds to a  DP of 0.6 mbar. However, to do this some hardware interlocks have to be temporarily overruled. Possible procedure: move detectors such that DP=-3 mbar (safety margin of 2 mbar to the lower limit of -5 mbar) cool to 10 o C with baseplate heating ON DP will become ≈0 mbar (safety margin of 2 mbar to the upper limit of +2 mbar) Without an active neon gas injection system cooling of the VELO to 10 o C implies: modify certain hardware interlocks quasi-constant surveillance of DP if needed, bypass some interlocks and adjust detector position to bring DP back in range, i.e. (-5,+2) mbar.