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The Field Quality Crisis Unit of the LHC main dipoles production

Peak of 10 units of multipole a2 in collared coil 1108

22nd April 2004, Manufacturer 1. Warm magnetic measurements of collared coil 1108 (see file) show a problem in measurement position 15 of aperture 1 and trigger yellow alarms on the even multipoles a2 of about 10 units (12 sigma). The observed pattern is confirmed by a short mole measurement with a coil of a pick-up length of 12.5 cm.

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The analysis of the inverse problem of the short mole measurement shows that this field anomaly is compatible for all multipoles with an inward radial movement of 0.45 mm (best fit) of block 6 in quadrant 4 (see Figure below).

17th March 04, Firm 1: The collared coil 1099 undergoes the procedure of disassembling in presence of  M. Cornelis and C. Vollinger from CERN. The removal of the rods has already taken place the day before and has been reported as unproblematic. In the region of the expected defect, a conductor movement of around 0.4 mm of block no. 6 radially inwards on a length of about 10 cm could be observed. Partially, the glue between the two windings and between the block and the adjacent copper wedge was not intact (see picture 1). From the short mole measurement, a second spot has been detected for which the inverse calculation gave no clear solution. The region of the second spot has been inspected visually the next day by Alstom personnel in the presence of M. Cornelis from CERN and it could be seen that the conductors of block no. 6 in the 1^st quadrant were not well glued to the copper wedge (see picture 2). This means, that these defects due to bad gluing are observed on both poles of this aperture.