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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 2065

15 March 2004, Manufacturer 2. Warm magnetic measurements of collared coil 2065 (see file) show a problem in measurement position 16 of aperture 1. The observed pattern is confirmed by a short mole measurement with a coil of a pick-up length of 12.5 cm. From the standard measurement, we see on the normal multipoles: b8 of 5.8 sigma, b12 of 5.7 sigma, b13 of 5.5 sigma, b14 of 4.7 sigma and on the skew multipoles: a6 of 6.7 sigma, a7 of 4 sigma, a8 of 4.9 sigma, a9 of 4.5 sigma, a12 of 6.7 sigma, a14 of 6 sigma.

First analysis shows that the defect is not following any symmetry, i.e. it is likely to be in one quadrant only. The analysis of the inverse problem applied to the worst position of the short mole measurement makes us expect to see an inward radial movement of block 6 of about 0.8 mm (see Figure below). Indeed, this movement does not justify the observed anomaly in b14 and leaves some small anomalies in a2, a6 a2 of 4 to 5.5 sigma. Therefore, additional small coil displacements could be expected in the defect area.

                       Fig.: Expected defect in CC 2065 is a conductor movement of block no. 6.

29 April 04, Firm 2: The collared coil 2065 undergoes the procedure of disassembling in presence of  F. Savary and C. Vollinger from CERN. The removal of the rods was unproblematic at about 550 bar. It has been decided to directly separate the poles and not to open the collared coil from the top, since the defect is very localized and is expected to cover a length of about 15 to 30 cm, only.

After separation of the poles, a radial movement of block no. 6 of about 0.5 mm inwards could be seen at the indicated spot. It is remarkable that block no. 6 was well glued to the copper wedge and fixed in this displaced position. Also, the glue between the two conductors of block no. 6 was fully intact.