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    8th Quench Behavior Team meeting

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    Minutes of the 8th meeting of the Quench Behavior Team

    Date: 2016-05-10, 09.00-10.30

    Place: 927

    Presents: P. Hagen, E. Todesco, S. Le Naour, O. Bruning, A. Verweij, R. van Weelderen, J. C. Perez, G. de Rijk

    Possible scenarios for training [E. Todesco, M Pojer]

    Ezio reviews the proposal for pushing the LHC towards 7 TeV by the end of 2015. The extrapolation based on the Gaussian assumption suggest to push towards 7 TeV sector 45, to know better the behavior of the second quench of 3000 series magnets. Pushing for training of a second sector to 7 TeV would allow to also gathering more quench statistics for the 2000 series magnets. Sector 12 has 2/3 of 2000 series magnets and is therefore a very interesting candidate to better see the statistics of 2000 series. Sector 23 could also be a good candidate since the sum of Sector 45 and Sector 23 magnets give an almost equal distribution between 1000, 2000 and 3000 series magnets.

    Paul Collier at the LMC of end of 2015 asked if we can consider warming up and cooling down one sector to have additional information on what happens at each long shut down if the magnets are warmed up. Ezio suggests that some sectors should be avoided, in particular 45 (50 quenches expected, too much risk), 78 (beginning of production, not representative for 3000 series), and 12 (only seven 3000 series magnets) and Sandrine points out the risk associated with quench heater failures that occurred after past thermal cycles and highlights that almost the whole machine will be warmed anyway up during LS2.

    Today we have data om the retraining after a thermal cycle relative to sector 56, pushed to 6.5 TeV in 2008 and 2015, and to sector 34, pushed to 6.0 TeV in 2008 and in 2015. Both sectors are compatible with a hypothesis of constant behavior (i.e., the training to be done after a thermal cycle is always the same) – but the statistics is low, and the error is large. Most of the present (Gerard, Arjan, Gijs, Ezio) consider that warming up and cooling down another sector would not add much information to what we have today, and that it is not worth the risk.  Arjan also points out that this would be a special, fast thermal cycle with no time spent at room temperature, and this could affect the memory check, if relaxation phenomena were relevant. It is therefore not even clear what one could conclude from such an additional data point in the magnet training history. A decision on pursuing a special training warm-up during the EYETS should only be taken if it can offer clear information that can lead to decisions prior to LS2 (where all sectors are warmed up anyway) and if the added information is worth the added risk for failures (e.g. quench heater failures and magnet shorts). The discussion could not identify a clear, strong argument for what additional information could be learned from such a warm-up apart from stating that it would provide additional information. So the general advice is not to ask for a thermal cycle at the end of the year.

    Mirko presented on May 4th a possible strategy to fit the additional training during the 2016-2017 EYETS (End Year Extended Technical Stop). The safer option is to train just before the stop, but only 5 days could be available for one sector. Cryogenic group could explore if one additional sector could be carried out in parallel. This would allow to make the 15-20 quenches, compared to the 20-25 needed for sector 12, or 45, or 23 (with an additional statistical error, and plus the unknown presence of second quenches). On the other hand, after the stop there is a wider possibility of training, but if something goes wrong this has a direct impact on the schedule. The warm up would also have a non-negligible impact on the schedule, with 12 additional weeks.

    Sandrine will present the expected situation for LS2 and a summary of the quench heater failure statistics in detail in one of the next meetings. For the moment it is planned to

    • Replace 15 dipoles for high internal splice resistance (three sectors: S12, S23 and S45)
    • Install the 11 T and the connection cryostat around point 2 and 8 (warm-up of S12, S23, S67 and S78)
    • Replace few LSS with missing correctors
    • Replacement of magnets with quench heater problems and aperture restrictions [ULO] (S23, S45 and S81)

                                                                                                                                      

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