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    7th Run II FiDeL meeting

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    Minutes of the 7th FiDeL RunII meeting

     

     

    Date: 2016-02-11

    Place: 30-7-10

     

    Presents:

      Ezio Todesco, Matteo Solfaroli Camillocci, Rogelio Tomas Garcia, Per Hagen, Michaela Schaumann, Ewen Maclean, Luca Bottura, Lucio Fiscarelli, Vittorio Remondino

     

    Precycle strategy for 2016 [M. Solfaroli Camillocci]

     

    Matteo makes a review of the precycle strategy used in Run II. With respect to the original document issued in 2010, the following modifications have been added

    • To avoid being dominated by the quadrupoles, both cell and insertion region, the ramp down is done with a faster exponential decay thanks to special steering of the power converters (see slide 5). This gives a faster ramp down with respect to the Run I. Therefore from Run I to Run II we can expect differences in the decay and snapback due not only to the increased energy but also to the faster ramp down.
    • Matteo reminds that with respect to the usual plot, taken from the PRSTAB papers of L. Bottura and N. Sammut, the preinjection porch at 350 A is eliminated: after the reset current at 100 A (where one can stay long to give access) one goes straight to injection energy.
    • Last element (trivial for those ones operating the LHC everyday but important to say) is that the precycle is used only in case of faults –otherwise previous physics cycle is used.

     

    In 2015 we did 230 precycles – among them we had 71 coming from cryogenics faults and 57 from QPS faults. Even though we can expect a reduction of the QPS faults, we still have a ~150 precycles expected in case of a smooth year of operation. With 2015 settings, one precycle lasts 60 minutes.

     

    The proposal is to have a precycle at 3.5 TeV, with a gain of about 25 minutes, so going from 60 to 35 minutes. With an expected number of 150 precycles, this would allow saving about 60 hours of operational time in 2016. The 3.5 TeV precycle ensures the same static model, the only difference being a different dynamic component in decay and snapback. The software part to enable to apply special setting in case of a precycle is being prepared and presents on special challenges. A special measurement of chromaticity and tune should be carried out to fix the decay and snapback correction for a precycle case.

     

    The only drawback of the 3.5 TeV precycle could be not to erase completely the previous powering history, so the reproducibility could become worse. Special measurements will be also carried out on a dipole. The strategy will be presented in LBOC and stamped in LMC before end of March.

     

    Nonlinear puzzles in the LHC [E. Maclean]

     

    Ewen gives an outlook on the nonlinear measurements and modeling in the 2015 run.

    • Second order chromaticity is well understood (at injection), when the MCO hysteresis and the second order effect of MCD on Q’’ is taken into account.
    • Third order chromaticity correction requires a reduction of the MCD powering of 40% (at injection) - this is not understood, since the local b5 correction implemented in the MCD settings should also correct Q’’’.

    In both cases it would be interesting to have a measurement also at top energy.

    For the triplet errors, measured at 6.5 TeV after squeeze at 40 cm:

    • The systematic component of b4 in the triplet (MQXA) gives a systematic amplitude dependent detuning: we measure only half of what expected. The squeeze of individual IP will clarify the uncertainties of the model.
    • Feed down effect of a3 and b3 are smaller than in the model.

    For dynamic aperture,we have simulation vs measurement in case of variable MCO (octupole spool piece), with visible degradation of dynamic aperture when going away from the nominal setting of -20 A. Agreement is good on the positive part of the current, and less good on the negative part.

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