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Nicholas J. Sammut

Decay Prediction and Minimisation During LHC Operation. Nicholas J. Sammut. Field Quality Working Group. with several contributions from L. Bottura, S. Sanfilippo, W. Venturini, R. Wolf, M. Di Castro. University of Malta. Outline. Standard LHC Cycle Decay Powering History

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Nicholas J. Sammut

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  1. Decay Prediction and Minimisation During LHC Operation Nicholas J. Sammut Field Quality Working Group with several contributions from L. Bottura, S. Sanfilippo, W. Venturini, R. Wolf,M. Di Castro University of Malta

  2. Outline • Standard LHC Cycle Decay • Powering History • Other Considerations • From Prediction to Optimisation 1/30

  3. 11850 A 11850 A 50A/s 760 A 350 A 10A/s to injection MB Decay 406 apertures for MB in Fidel repository (16%) pre-cycle of 50A/s MB 2/30

  4. MB Decay 3/30

  5. MQ Decay 24 apertures for MQ (3%)  =216s 11850 A 11850 A 50A/s 760 A 350 A 10A/s to injection 4/30

  6. MQM Decay 6 apertures for MQM (8%)  =435s T = 1.9K 5390 A 5390 A 20A/s 265 A 50 A 10A/s to injection Block 4 Courtesy W. Venturini 5/30

  7. MQY Decay 16 apertures for MQY (33%)  =184s 3610 A 3610 A 20A/s 176 A 50 A 10A/s to injection Courtesy S. Sanfilippo, M. Di Castro 6/30

  8. Quadrupoles Decay after 10000s injection Preliminary data: only 1 measurement MQ MQM  =1270s  =1391s MQY  =138s Courtesy S. Sanfilippo, M. Di Castro 7/30

  9. Decay Scaling Law • Used in case the model needs to be tweaked • Used to allow a single reference dipole to be representative of the whole magnet population 8/30

  10. Decay Scaling Law Error Maximum error follows a lognormal distribution MBs Median error - b1 0.5 units - b3 0.06 units - b5 0.02 units 9/30

  11. Outline • Standard LHC Cycle Decay • Powering History • Other Considerations • From Prediction to Optimisation 10/30

  12. Powering History 11/30

  13. MB Flat Top Current Dependence effects modelled magnitude of effects 12/30

  14. MB Flat-Top Time and Pre-inj Time Dependence 13/30

  15. MB Surface Fit for b3 Median Error 14/30

  16. Quadrupole Flat-Top Current Dependence Preliminary data: only 1 measurement (2 ap) MQ MQM MQY Courtesy S. Sanfilippo, M. Di Castro 15/30

  17. MQ Flat-Top Time Dependence Preliminary data: only 1 measurement (2 ap) MQ Courtesy S. Sanfilippo, M. Di Castro 16/30

  18. Pre-cycle Ramp Rate Dependence Preliminary data: 4 apertures Measurements to be done on MB,MQ, MQY, MQM (Given low priority) 17/30

  19. Outline • Standard LHC Cycle Decay • Powering History • Other Considerations • From Prediction to Optimisation 18/30

  20. Ap 1 Ap 2 Decay Vs Injection Currents (MQY) • The higher the injection , the lower the decay • Working at 144 A leads to an increase • of the b2 decay amplitude by 14 %. Courtesy S. Sanfilippo, M. Di Castro 19/30

  21. Decay Vs Injection Currents (MQY) In this current range the variation of the decay amplitude is almost linear. Courtesy S. Sanfilippo, M. Di Castro 20/30

  22. Multiple LHC Cycle Effects Performed on 2 aps B1 difference is less than measurement repeatability Maximum difference between two consecutive cycles is 0.05 units for b3 Decay time constants show that any history more than 2000s has a negligible effect on decay 21/30

  23. Magnet Aging Performed on 2 aps • MB1017 - magnetic measurement in April 2003 • - magnetic measurement in September 2005 28 months 0.07 0.01 0.02 Effect is small within measurement uncertainty but still larger than measurement repeatability 22/30

  24. Outline • Standard LHC Cycle Decay • Powering History • Other Considerations • From Prediction to Optimisation 23/30

  25. From Prediction to Optimisation - FIDEL is designed to forecast the harmonics during the LHC cycle within constrained powering scenarios - FIDEL measurements were not designed to optimise the cycles to reduce the dynamic effects (decay). - However a measurement campaign substantiated by simulations (CUDI – See A. Verweij talk) will indicate how decay could be minimized. - Measurements so far indicate that pre-cycle with short flat-top time, low top current and long pre-injection time reduce the decay provided there is nothing else in a window of 2000s 24/30

  26. Study of Optimisation Cycles I (A) I (A) t (s) t (s) I (A) I (A) t (s) t (s) I (A) t (s) 25/30

  27. Study of Optimisation Cycles Optimisation study will tackle the following questions: How do we minimize the decay? How do we power other magnet families whilst we wait for the preparation of the slowest ramping magnets? How do we guarantee reproducibility? What is the priority of these measurements?? Still work to do on MQ, MQM, MQY, correctors 26/30

  28. Degaussing Cycles b3-b5 Hall probe Courtesy W. Venturini Multipoles tend to the geometric value after degaussing Allowed multipoles are largely affected by the degaussing Allowed multipoles have negligible decay after degaussing (0.05 units) Does not require pre-cycling Degaussing is associated with a large variation of the allowed multipoles at the beginning of the energy ramp, equal to the persistent current magnetisation (7 units of b3) 27/30

  29. Degaussing Cycles vs Standard LHC Cycle 28/30

  30. Degaussing Correlation with Geometric Allowed multipoles are close to the geometric values Shift of 0.76 units for b3 perhaps due to residual magnetisation 29/30

  31. Discussion 30/30

  32. Addendum: Rotating Coils Dipole Rotating Coils Quadrupole Rotating Coils Ceramic sector of 15m long shaft Dipole 3 coils for absolute and compensated measurement Quadrupole 5 coils for absolute and compensated measurement Precise & integrated over magnet length, but not fast enough for snapback… 31/30

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