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The Field Quality Crisis Unit of the LHC main dipoles production

Inner radial shift of conductor block in collared coil 3175

22nd April 2004, Manufacturer 3. Warm magnetic measurements of collared coil 3175 (see file) shows yellow alarms in measurement position 14  in 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 in position 14 on the normal multipoles: b8 of 6.1 sigma, b12 of 5.9 sigma, b13 of 5.3 sigma, b14 of 7.4 sigma, and on the skew multipoles: a6 of 5.8 sigma, a12 of 5.3 sigma, and a14 of 5.6 sigma.

The analysis of the inverse problem shows that the field anomaly of aperture 1, pos. 14 is compatible for all multipoles (except b14) with an inward radial movement of block no. 6 of at least 0.4 mm (best fit; see Figure below) in the 3rd quadrant. In addition, the short mole measurement picked up another spot in the same aperture which could be calculated back to an expected movement of block no. 6 of about 0.2 to 0.25 mm in the 4th quadrant.

     Fig.: Expected defect in CC 3175, ap. 1, position 14 is a conductor movement of block no. 6.

11th May 04, Firm 3:  The collared coil 3175 undergoes the procedure of disassembling in presence of P. Fessia and C. Vollinger from CERN. The coil protection sheets are removed and the poles of aperture 1 are separated. After separation of the poles, a defect in the region of measurement position 14 in the 3rd quadrant can be observed. Block no. 6 is loose on a length of about 0.7 m (not glued to the adjacent copper wedge). The glue between the two conductors of block no. 6 is fully intact. A small movement of the block of about 0.2 mm is still visible.

Then, the second spot is inspected and also in this position loose conductors of block no. 6 on a length of about 20 cm could be seen during visual inspection and a repair of this second spot will be carried out as well.