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Observations regarding chromaticity correction during May 2011

This report presents an analysis of chromaticity correction during May 2011 at CERN. We examined the time spent in preparation and flattop during 68 ramp cases, with a focus on the effects of using actual pre-cycles. Findings indicate that 75% of ramps had preparation times of 15-30 minutes, with significant implications for chromaticity correction efficacy, especially for ramps with long flattops. We highlight the correlation between preparation duration and drift, emphasizing the need for optimized correction methods to enhance stability and performance in particle acceleration systems.

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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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