4.2.1 Cerenkov Counters (CER)
Each secondary beam is equipped with one or two threshold Cerenkov Counter (CER). Its length and position in the beam is shown on Fig. 1. Its mechanical characteristics are shown on drawing EP 82.550. The upstream and downstream windows are made of Mylar sheets, thickness 0.6 mm each. The CER may be filled with non-flammable gases, e.g., CO2, He, Ar, N2.... to a maximum overpressure of 3.3 bars (0.33 MPa). The gas bottles, if not left over from previous run, must be provided by the beam user ; they can usually be purchased from the CERN gas store. The filling panels and gas bottles are located outside of the test areas, the Gas Distribution Rack (GSD) is located next to the Beam Control Room EBCR.
The synoptic scheme engraved on the front panel of the GSD indicates the order of the operations. The user must proceed according to the rules fixed by the CERN GENERAL SAFETY CODE.
When changing the filling, make sure no overpressure is left, open the leak valve ("FUITE") before switching ON the vacuum pump. Flushing the counter several times after ten minutes pumping is more effective than pumping a long time.
All CER installed in the East Hall have been fitted with UV sensitive PMs model XP2020Q. The HT should never exceed 2 kV, the power supplies are in E BCR. Every user should run his own signal cable to the CER. If both outputs are used, make sure they are properly terminated.