Tilt of the field angle in some cold masses from Firm 1

30 October 2002, CERN. The magnetic field analysis of the cold mass shows a variation of the field direction along the longitudinal axis with respect to average of up to 6 mrad, that is out of tolerance (3 mrad), and out of statistics of 6 sigma, (see xls-file). The geometric measurements are also out of bounds (see xls-file). Cold mass 1021 is therefore held.

early November 2002: Meeting of the crisis unit: F. Savary, W. Scandale, E. Wildner, G. Gubello, M. Bajko, R. Chamizo, M. Cornelis. A study (G.Gubello, doc-file)) is presented showing a very strong correlation between the magnetic field angle and the geometric twist for large twist angles. The tolerance for the geometric twist is 3 mrad locally (4 is accepted) and magnet 1021 had 8 mrad of geometric twist. Such a large twist implies difficulties to keep the center of the beam tube whithin the 1 mm toroid. It is decided to cut the shell and reassemble the cold mass.

28th February 2003, Firm1. The cold mass is reassembled and welded; measurements (See xls-file) show a large improvement of the cold mass twist.

28th February 2003, Firm1. The cold mass is reassembled and welded; measurements (see xls-file) show a large improvement of the cold mass twist.

23th May 2003, CERN. Magnetic measurements of cold mass 1037 show another case of bad main field direction (see xls-file). Variations along the axis are up to 10 mrad. The project engineer ask for unwelding of the cold mass. A meeting is called (presents: Gijs De Rijk, Elena Wildner, Michele Modena, Christine Vollinger, Walter Scandale, Iouri Vanenkov, Marc Cornelis, Ezio Todesco) to inform and discuss the situation. Elena Wildner recalls that the main field angle indicator defined by Stephane Fartoukh gives 0.28 for this magnet, i.e. well above the 0.18 warning limit (six magnets with more than the 0.18 limit cannot be installed in the same cell). Michele Modena recalls that the tolerance in the specification on the main field direction variations along the axis was 3 mrad, and then it has been widened to 6 mrad.

(... we hope not, but perhaps it has to be continued ...)