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    Special meeting on the results of the cold tests of MBHA-001 - Update 16

    → Europe/Zurich
    Frederic Savary (CERN)
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    Minutes of meeting

    1. Participants:
      D. Baffari, M. Bajko, M. J. Bednarek, B. Bordini, L Bottura, M. Buzio, A. Devred, M. Duda, A. Foussat, R. Keijzer, J. Ludwin, F. J. Mangiarotti, M. Martino, H. Prin, E. Ravaioli, F. Savary, J. Steckert, S. F. Troitino, A. Verweij, G. Willering, S. Yammine
       
    2. Key points or questions raised during the discussion:
       
      • Spikes in magnet models [Michal]
        • Is there any difference in the signals/spikes when ramping up and ramping down. Luca suggests producing plots "signal vs dI/dt";
        • Emmanuele asks how reproducible is the longitudinal position of the spikes (QA signals);
        • If there are flux jumps in the middle of the coil, it means that it is still superconducting;
        • On slide 8, Luca asks whether it is expected to observe top/bottom symmetry of the signals.
      • MBHA-001 quench antenna signal analysis [Franco]
        • QA spikes are correlated with coil spikes (voltage) and the correlation is very consistent between the different tests;
        • Spikes are mostly of the “gradient” type, and not of the “dipole” type.
      • Results of FEM simulations of Sudden Flux Variations [Dario]
        • If the spikes are due to the demagnetization of the conductor, this demagnetization has to occur inside the magnet and has to be symmetric with respect to the two apertures. It needs to be big and global.
      • Intermittent short - measurement results [Mateusz]
        • The switching time of the current in the short depends slightly on the ramp rate, but not on the current direction;
        • The current in the 50-ohm resistor is proportional tot the ramp rate.
      • Impedance measurements [Jaromir]
        • Low spikes activity was observed during 13 kHz  measurements. Before this test, the magnet was cycled many times between 1.5 and 2.5 kA for the intermittent fault tests. It is recalled that in March 2020, a lot of spikes were visible at 6 kHz.
           
    3. Executive summary:
    • There is limited time to carry out additional tests on S2-LMBHA001, likely not more than a week as from 15 June.
    • The following tests are important: lifted voltage, impedance measurements at other frequencies (also at 13 kHz without pre-cycles), artificial intermittent short test in different conditions (ref. to the proposals by Emmanuele, and Luca's comment on the fact that we would like to demonstrate whether or not an intermittent short is consistent with the findings during the various 9 kA discharges, e.g. the amplitude and morphology of the spikes do not depend on the voltage across the coils).
    • The 9 kA discharge carried out after the intermittent short tests, and resulting in no spikes is an interesting case that we should investigate further in order to understand it better.
    • A standard discharge at 9 kA with the magnet "cleaned" beforehand would be useful.
    • The summary table has to be updated, expanded, in light of the what we know today (action Frédéric).
    • We need to draw out conclusions rather quickly. For this, the selection of the tests to be carried out is critical, to be thought carefully, between performance related tests, and those related to spikes.
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