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Observations regarding chromaticity correction during May 2011

CERN, FiDeL meeting, 14 th June 2011. Observations regarding chromaticity correction during May 2011. Nicholas Aquilina TE-MSC-MDA Acknowledgements: M. Strzelczyk, M. Lamont, E. Todesco. Overview. What is the time spent at preparation and flattop?

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Observations regarding chromaticity correction during May 2011

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  1. CERN, FiDeL meeting, 14thJune 2011 Observations regarding chromaticity correction during May 2011 Nicholas Aquilina TE-MSC-MDA Acknowledgements: M. Strzelczyk, M. Lamont, E. Todesco

  2. Overview • What is the time spent at preparation and flattop? • Spool pieces, what correction are we applying? • Behaviours of ramps using an actual pre-cycle • Behaviours of ramps using previous physics run as a pre-cycle (in particular with flattop time > 10 hours)

  3. Preparation and flattop time • 68 ramps analysed, the ramps during May 2011 • 75% of the cases have a preparation time between 15’-30’ • The ramps which are pre-cycled using an actual pre-cycle have a flattop time of 10’,tFT* refers to the flattop time of the physics ramps • SM18 measurements and the proposed MD measurements follow the trend in the machine Preparation and flattop time in May 2011 (pre-cycles excluded) Preparation and flattop time in May 2011 (pre-cycles included) tFT tFT tinj tprep

  4. Correction in the spool pieces • Dynamic correction applied by the spool pieces was found to be the same (within a fraction of ampere – [why ?]) for all cases analysed Averagecurrent in the MCS at injection in May 2011

  5. Cases with actual pre-cycle 1755 1813 1800 • 32% (22 cases) of the 68 ramps were pre-cycled with an actual pre-cycle • In the plot the trims are removed, if the chroma is flat the spool piece correction works well • Worst case (and unique) fill 1800, drift of 5 units 1787 N.B. drift is the amount of decay observed in the given data

  6. Cases with long flattop (>10hours) • 6 cases analysed, all with flattop > 10 hours • The cases with preparation time less than 35 minutes drifted by about 5 units (under corrected) • The case with long preparation time (fill 1805) was more stable (slightly overcorrected)

  7. Cases with long flattop (>10hours) 1784 1789 1804 1805 1839 1784 1789 1804 1805 1839 1784 1789 1804 1805 1839 1784 1789 1804 1805 1839

  8. Where are we?? Slightly overcorrected tFT > 600’ tprep = 239’ c = -2, decrease correction by 10% Undercorrected: drift of 5 units tFT > 600’ tprep 20’ – 35’ c = 9, increase correction by 50% Undercorrected tFT = 10’ tprep = 1’ c = 9, increase correction by 50% OK tFT = 10’ tprep 15’ – 20’ c = 0 – perfect! c is the decay amplitude at t →∞ c as found in previous analysis was 18 units

  9. Where are we?? Numerical data

  10. Conclusions • 75 % of the cases have a preparation time between 15’-30’ • Using an actual pre-cycle before a ramp ensures good correction of the chromaticity (60% of cases where within 1 unit) if the preparation time is longer than 10 minutes • Drift of 5 units was observed in cases with long flattop (> 10 hours) • Having long preparation time reduces decay which can lead to overcorrection

  11. Conclusions • The poweringhistory influence on decayisstrongerthanwhatwe have today in FiDeL • Beammeasurements show consistent results – reproducibilitywithin 1-2 units if poweringhistoryis the same • An update of the coefficients will be given at the end of June

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