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3 Mechanical Design
3.4 Phototube boxes
The design of the phototube containers is shown in fig. A-3 of Appendix A. They are modified versions of the tested design of the TOF containers. Inside the container the PMT is positioned at 20 mm distance from the end, surrounded by a metallic box in order to be protected from the magnetic field. A reflective surface of truncated pyramidal shape is added in order to increase the light collection efficiency to the PMT. The magnetic shield is made of 0.5 mm thick mu-metal[4] and dimensions 75x30 mm2. The material to be used is the same as used in the AMS-TOF system. Figure 3-1 [3-1] shows the calculated B field at z = 860 mm (AMS Coordinates) which is approximately the location of the PMT's of the upper ATC layer. The three components of the magnetic field are included in Appendix C. The magnetic field is estimated to be always lower than 200 Gauss, therefore the same material used in the TOF system can be used. In case the magnetic field measurements show that the field is higher, additional wrapping with a special mu-metal tape will be used to compensate. We expect that even in this pessimistic scenario only a few PMT's of the upper layer will be wrapped with the mu-metal tape. The magnetic field at the location of the PMT's of the lower layer is shown in fig. 3-2. A measurement of the magnetic field at the locations of the PMT's is under way at ETH-Zurich by the AMS Integration Group[5].
Figure 3-1 Calculated B field at z=860 mm from the start of the AMS Coordinate system.
Figure 3-2 Calculated B field at z=1040 mm from the start of the AMS Coordinate System. The total field is always less than 100 Gauss.
[4] Order to Vacuumschmeltz under way
[5] Contact G.Viertel, ETH-Zurich
Issue: Draft - Revision: 04 - Last Modified: 20 April 1997