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The Field Quality Crisis Unit of the LHC main dipoles production

Inner radial movement of a conductor block in collared coil 2089

18th May 2004, Manufacturer 2. Warm magnetic measurements of collared coil 2089 (see file) show a problem in measurement position 3 of aperture 1 and trigger yellow alarms on b8 and b 12 (4.4 and 4.6 sigma). The analysis of the inverse problem shows that this field anomaly is compatible for all multipoles with an inward radial movement of 0.3 mm (best fit) of block 6 in quadrant 2 (see Figure below). The calculated frame for the movement is 0.1 to 0.4 mm.

         Fig.: Expected defect in CC 2089 is a conductor movement of block no. 6.

1st June 04, Firm 2: The collared coil 2089 undergoes the procedure of disassembling in presence of  M. Bajko, F. Savary and C. Vollinger from CERN. The removal of the rods has already taken place the day before and has been reported as unproblematic. We observed that there was no gap between the inner layer and the cold bore tube in the predicted defect zone (we could not pass in there a sheet of paper whereas the gap was clearly visible in the neighbouring zones).

 It has been decided to directly separate the poles of aperture 1 and not to open the collared coil from the top, since the defect is very localized. In the position of the expected defect, a conductor movement of the order of 0.1 mm on a total length of about 1 m was measured instead of the best fit value of 0.3 mm with a layer of polyimide of 100 μm and a lamination of the winding mandrel.

It could be verified that the adhesion of the polyimide was very good on the entire length of the affected coil between the first 2 turns and between the second turn and the copper wedge. Also the straightness of the inner layer has been checked with a ruler in the suspected area and no deformation could be seen.