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    11T Quench Heaters Trace to Wire Jointing

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    Minutes of Meeting

    Participants:

    A. Devred, S. Izquierdo Bermudez (part time), J. Ludwin (external expert), A. Milanese (part time), R. Principe, F. Savary, D. Tommasini (external expert)

    Excused:

    M. Bednarek (external expert), L. Bottura, L. Grand Clement, F. Rodriguez Mateos (external expert)

    Distribution:

    Participants, excused, A. Foussat, H. Prin, C. Scheuerlein

    Foreword:

    This meeting was called following the NCR described in the EDMS document #2311125. A failure occurred during the reception tests at cold of the magnet S3-LMBHA002 in SM18. More precisely, one of the QH circuits of the coil GE14 (CC06) did not pass the third discharge test. Subsequent tests (time-domain reflectometry) carried out at different stages of the magnet tests and dismounting (on the cryo-magnet when it was on the bench in SM18, on the cold mass assembly, and then on the collared coil assembly) have indicated that the circuit was open close to the trace to wire jointing.

    The goal of the meeting was to review with external experts the 11T trace to wire jointing procedure, the NCR, and the action plan proposed by LMF / WP11 in order to (1) consolidate the current design before any jointing is done on the next coils, which are either in production or to come, and (2) reassure ourselves on the current design that has been used in the magnets S1 (impregnated QHs), S4 (external QHs), and S5 (external QHs). The magnets S4 and S5 are now the ones proposed for installation in the LHC, upon condition of satisfactory results of the performance tests.

    Minutes

    The concept and the procedure followed for the soldering of the pin connector to the trace terminal were described for the 11T dipole prototype, and the series magnets made to date (S1 to S5). 

    The external experts have given the following comments and suggestions.

    1. Given the relatively small area surface of the contact between the pin and the trace terminal (5 mm2), the concept does not feature comfortable margin and is likely sensitive as to possible imperfections affecting the soldered joint, which may arise from poor execution of the work;

    2. The locking of the jointing w.r.t. the saddle should be avoided. In case of relative movement between the jointing and the wiring, or between the jointing and the trace, the soldered joint will be mechanically loaded, and consequently might break. It could possibly be a progressive failure mechanism.

    As to point 1, it was suggested to increase as much as possible the area surface of the contact between the pin and the trace terminal and to increase the volume of solder, for example by soldering the pin parallel to the trace terminal on its entire length. In this respect, the alternative solution based on the utilisation of flat connectors would be better (see slide 20 of the presentation).

    As to point 2, it was suggested to increase the diameter of the hole in the saddle, should the pin connector concept be used again, or simply avoid this lock.

    Although it is clear for the project team that the jointing area is well secured, once embedded in resin, i.e. there should not be local relative movement between the trace and the pin connector (which are soldered together), the external reviewers have expressed concerns because, according to them, micro-movements can be sufficient to provoke damages to the soldered joint. In order to verify the mechanical strength of the assembly, it was suggested to carry out mechanical tests during which (1) one pulls on the wiring sticking out from the saddle, the saddle being fixed, and (2) one pulls on the trace, the saddle being fixed, in order to make sure the jointing area is not affected in none of these cases.

    The project team (LMF / WP11) will develop a solution based on the utilisation of flat connectors.

    The trace to wire jointing cannot be changed in the already finished magnets, S1, S4, and S5. To reassure on these cases, the project team will organise mechanical and electrical tests, including fatigue tests aiming at demonstrating fit-for-purpose, lifetime, and margin of the current concept based on the pin connector.

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