CERN, FiDeL meeting, 30th August 2011 Change of the powering history from chromaticity decay: Update on beam measurements Nicholas Aquilina TE-MSC-MDA Acknowledgements: E. Todesco, M. Strzelczyk
Powering history scaling law • Free parameters: T0, T1, τT, P0, P1, τP • T0 and T1 and similarly P0 and P1 are in reality one parameter, therefore a total of 4 free parameters • These parameters were obtained from beam-based measurements done during May and June 2011.
Scaling law parameters • These are the latest parameters in our database and in LSA • Time constants increased by a factor of 4, therefore the decay amplitude dependence on the powering history is longer than observed in magnetic measurements
Checking with beam measurements • This update was implemented in the machine at the beginning of July (after the technical stop) • Some ramps during July and August were used to check how effective the correction is • Two things were checked: • Scaling factor as applied by the LSA is inline with our model? • The chromaticity decay was: corrected, under-corrected or over-corrected?
Fills analysed N.B. in most of the cases the data available was of 2000 s
Fills anaylsed Within 1 unit Slightly overcorrected Overcorrected by 11% Overcorrected by 28% Within 1 unit
Fills analysed actual pre-cycle within 1 unit over corrected not enough data
Comparison between expected and actual behaviour of the scaling factor • Observe how the scaling factor as applied through LSA is always about 95% of that calculated with our model * Taking decay at ∞ at standard condition = 15.75 units of chromaticity
Conclusions • Pre-cycled cases with actual pre-cycle are being well corrected • Long fills; more cases need to be analysed, more chromaticity measurements are required • To understand why the scaling factor as applied by LSA is 95% of that obtained through our model