A missing shim in magnet 1005 ?

29 october 2002, Manufacturer 1. Warm magnetic measurements of collared coil 1027 (see file) show a spike in b2 (red alarm, i.e. more than 8 sigma) and a yellow alarm in b3, a2 (yellow alarm, i.e. between 4 and 8 sigma) in position 8. Position 7 is in between - this seems to indicate that the problem is not related to the measure, but that something wrong is in the magnet. The error is in all multipoles, i.e. no symmetry is followed: this means that it should be in one quadrant only. Moreover, only the low order multipoles are affected: this means that the source of error should be far from the aperture (i.e. outer layer). Simulations by E. Todesco on november 1 show that a missing shim of 0.8 mm fits well the numerical data. A. Devred confirms these results using a different code.

6 november 2002, Manufacturer 1. The measurement is repeated, giving similar results.

7 november 2002, CERN. Meeting of the crisis unit: J. Vlogaert, W. Scandale, M. Cornelis, J. Rinn, C. Voellinger, E. Todesco, P. Fessia, J. Miles, A. Devred. The case is illustrated by E. Todesco and A. Devred. Even though the effect is much weaker than for 1002, the numerical evidence of a missing shim is strong. Foreseen location of the missing shim: aperture 1, right side, lower pole, outer layer. The decision of decollaring the magnet is taken. Wide discussions about the necessity of replacing the mass insulation and quench heaters, as indicated in the specification. WS asks for a double measure of field quality is the cold bore will have to be re-worked due to deformations.

(... to be continued ...)