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    OMC-BI meeting: LHC BPMs

    → Europe/Zurich
    6/2-008 (CERN)

    6/2-008

    CERN

    15
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    People: Manfred, Marek, Ana, Jacqueline, Lukas, Rogelio, Thibaut

    LHC BPMs

     

    Ana, Calibration factor

    Arc calibration factors  are within specs. IR1&5 calibration factor is offset and has outlayers. 

    Provide IR BPMs with largest calibration error and even excel.

    Thibaut mentioned that one possible explanation could be the length of the cables in the IR. Manfred agrees there are cable issues. The use of the right polinomials in FESA should be re-checked in the IR.

    Typical peak-to-peak amplitudes are 2mm in the arc.

     

    Elena, noise and bad BPMs

    Manfred found that 7R1.B1 had a bad connection (cryostat is open now) and we see it as bad too. Good match.

    The BPM electronic status should be logged in Timber and should be used in measurements to avoid using bad BPMs. Thibaut says that there are 2 types of alarms during the electronic calibration (yellow and red). Thibaut et al will check if this is logged. 

    Ageing in the comparator of the BPM is a real problem that manifests mostly in low intensity beams.

    Manfred proposes to compare pilot and nominal signals with same type of excitation. The transistor problem would show up. -> MD in 2021

    The single critical one failing BPM is the Q1 Beam 2 right of 5 vertical (BPMSW.1R5), but DOROS is working.

    One could run a calibration now and try to identify the problem now.

    BI is overloaded, what actions are prioritized:

    -Few highly critical BPMs BPMSW.1R5 (V B2)

    -Exchange of bad BPMs data between electronic calibration and beam based possibly to ellucidate a list of 'very bad bpms' to fix now

     

    Lukas, news on noise

    Pilot: arc BPM noise is 100 um. IR BPMs have 200um noise. It is within specifications.

    The ageing issue above could materialize in the noise level, to be looked at this for the future to monitor ageing.

    Crate-correlated-noise  is not yet observed, further studies will be done.

    Thibaut mentions that BPM H&V offsets were measured wrt to beam chamber, the data is available in MTF.

    Data of the polinomials for the BPM calibration is also available in MTF.

    -> Ask Manuel Berguez has all MTF data (Christian Boccard).

     

    Manfred argues for HL-LHC. The goal would be 10um resolution for HL. The calibration issue in LHC is not yet known and should be first clarified not to have same error in HL. -> FESA class polynomials will be checked. Actually it could be that orbit mode is well corrected but not in turn-by-turn-> Very important to check.

    Thibaut is almost sure that this is not done for TbT for computational reasons. To be further discuss how to fix this.

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

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