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    5th Run II FiDeL meeting

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    Minutes of the 5th FiDeL RunII meeting

     

     

    Date: 2015-07-29

    Place: 927

     

    Presents:

      Per Hagen, Ezio Todesco, Rogelio Tomas Garcia, Ewen Maclean, Benoit Salvant

     

    Compensation of sextupole components without 78 sector [P. Hagen]

     

    Due to the recent problems with beam 2 sextupole spool pieces circuit in 78, it is being considered to condemn the circuit and compensate with the other ones. One possibility is to use the other spool pieces circuits. Per shows that the 78 has the feature of having 2 units larger b3 component at 6.5 TeV (4.5 instead of 2.5 units) since it contains the beginning of the production, done with the first and second cross-section types. The global compensation can be done through increasing the current of the other spool pieces circuits (30 A more at 6.5 TeV). Rogelio points out that for the beam dynamics, the correction is more critical at injection. A proposal will be done at LMC of the same day (July 29th) by M. Giovannozzi.

     

     

    Nonlinear chromaticity – episode II [E. Maclean]

     

    This is a follow up of the previous talk given on July 14th. In that meeting, it was shown that the beam based correction to minimize Q’’’ is giving a MCD setting with about half of the current needed to have the local compensation of b5 errors in the dipole (our baseline in LS1). Now Ewen is investigating this issue. Using the MAD code with a correction of the average b5, he founds that Q’’’ is not perfectly corrected, but a 10% residual is left. On the other hand, using the Q’’’ correction found with the beam measurements, the Q’’’ estimated in MAD is close to zero. Summarizing (slides 4), using the complete MAD model with the maximum of information on magnetic errors and alignement, the Q’’ term agrees within 30%, but the Q’’’ term is off by a factor 3 in H and a factor 10 in V. So the main source of this high order term is still not understood. To be continued …

     

    MSC studies [B. Salvant]

     

    In April 2015 a special measurement has been done during commissioning. In sector 12 a orbit bump has been created to check the efficiency of the correction of b3 errors with spool pieces. In case of bad correction, a residual b3 would be left and the bump would generate tune adding coherently. The main result is that the correction is optimal with a maximum 10% error. A similar measurement for the other sectors is planned.

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