Session 3: Procedures to Follow-up Production and Checkpoints

Session Chair: Louis Walckiers, Scientific Secretary: Christine Vollinger

Luc Oberli: Follow-up and Checkpoints of Cable Properties

Luc Oberli gave a presentation on the relevant cable properties with respect to field quality issues namely the cable dimensions, the cable magnetization and the inter-strand cross-contact resistance. Further, he showed and explained the existing four holding points, which are set during the follow-up of the cable production. From the measurements taken at CERN in the framework of the cable follow-up, the main parameters of the cable dimensions, the magnetization values and the inter-strand cross-section resistance are all within tolerances and the control of these values is well covered by means of the existing holding points.

Elena Wildner: Follow-up and Checkpoints of Harmonics in the Collared Coils and Cold Masses

Elena Wildner presented the holding points for the control of the field quality for the LHC main dipoles during production. These are warm magnetic field measurements carried out at the three manufacturers that are analysed at CERN to steer the field quality towards the beam dynamics limit at an early stage of production. Two holding points exist, the first one for the collared coil assembly and the second one for the cold mass assembly. The analysed results are stored in an ORACLE database and the original Excel file is kept in a repository to be accessed on the web. The resulting multipole curves are collected in a bimonthly report. All data goes into MTF when the magnet arrives at CERN.

So far, 100 % of the collared coils and 98 % of the cold masses have been measured. The performed analysis allowed the detection of both measurement and assembly problems and seems to be a suitable tool for the control and the steering of the field quality of the dipole production.

Laurent Deniau: Follow-up and Checkpointsfor LHC Cryomagnets

Laurent Deniau showed the follow-up and checkpoints, which are carried out on the LHC cryomagnets in order to control their field quality. The talk started by a reminder of the standard magnetic measurement test program performed by the MTM group which is composed of the current cycles so called “full loadline”, “ramp” and “machine cycle”. The analysis of the 15000 measurements that are performed during these cycles provides a good knowledge of the field quality under different conditions, including the machine operation. Among others, the processed data deliver the local and integral field harmonics, the field angle, and the transfer function, as well as the static field errors induced by geometric contribution, persistent currents, and iron saturation augmented by the dynamic field errors which result from the cable coupling currents during the ramping of the current. From these parameters, different data representation and plots may be built to summarize the field quality of both a single magnet or a sequence of magnets. This includes warm-cold correlation for quality control cross check. A synthesis of these views is put into the cryomagnet Id Card used by the Magnet Evaluation Board for magnet acceptance.

As a conclusion, it was underlined that neither conformity nor non-conformity can be triggered from magnet field quality measured in cold conditions. Moreover, at present the expected delay between warm and cold testing is of the order of few months. Therefore, the feedback for the production cannot come directly from cold measurements. Cold measurements are hence mainly aimed at quantifying and identifying drifts in error sources that cannot be monitored in warm conditions (like persistent currents, iron saturation, cable eddy currents, decay and snap-back and changes of the geometry under Lorentz forces) and provide the basis for extrapolation as well as quality control through warm/cold correlation.

Minutes by Christine Vollinger