1. 17 th April 2007 Nicholas J. Sammut Decay Prediction and Minimisation During LHC Operation University of Malta Field Quality Working Group with several contributions from L. Bottura, S. Sanfilippo, W. Venturini, R. Wolf, M. Di Castro

2. Nicholas J. SammutFQWG – Decay Prediction and Minimisation During LHC Operation 17 th April 2007 Outline Standard LHC Cycle Decay Powering History Other Considerations From Prediction to Optimisation 1/30

3. Nicholas J. SammutFQWG – Decay Prediction and Minimisation During LHC Operation 17 th April 2007 MB Decay 406 apertures for MB in Fidel repository (16%) MB pre-cycle of 50A/s 11850 A 50A/s 10A/s to injection 760 A 11850 A 350 A 2/30

4. Nicholas J. SammutFQWG – Decay Prediction and Minimisation During LHC Operation 17 th April 2007 MB Decay 3/30

5. Nicholas J. SammutFQWG – Decay Prediction and Minimisation During LHC Operation 17 th April 2007 MQ Decay 24 apertures for MQ (3%) 11850 A 50A/s 10A/s to injection 760 A 11850 A 350 A  =216s 4/30

6. Nicholas J. SammutFQWG – Decay Prediction and Minimisation During LHC Operation 17 th April 2007 MQM Decay 6 apertures for MQM (8%) 5390 A 20A/s 10A/s to injection 265 A 5390 A 50 A T = 1.9K  =435s Block 4 Courtesy W. Venturini 5/30

7. Nicholas J. SammutFQWG – Decay Prediction and Minimisation During LHC Operation 17 th April 2007 MQY Decay 16 apertures for MQY (33%) 3610 A 20A/s 10A/s to injection 176 A 3610 A 50 A  =184s Courtesy S. Sanfilippo, M. Di Castro 6/30

8. Nicholas J. SammutFQWG – Decay Prediction and Minimisation During LHC Operation 17 th April 2007 Quadrupoles Decay after 10000s injection MQ MQY MQM Preliminary data: only 1 measurement Courtesy S. Sanfilippo, M. Di Castro  =1391s  =138s  =1270s 7/30

9. Nicholas J. SammutFQWG – Decay Prediction and Minimisation During LHC Operation 17 th April 2007 - Used in case the model needs to be tweaked - Used to allow a single reference dipole to be representative of the whole magnet population Decay Scaling Law 8/30

10. Nicholas J. SammutFQWG – Decay Prediction and Minimisation During LHC Operation 17 th April 2007 Median error - b 1  0.5 units - b 3  0.06 units - b 5  0.02 units Maximum error follows a lognormal distribution MBs Decay Scaling Law Error 9/30

11. Nicholas J. SammutFQWG – Decay Prediction and Minimisation During LHC Operation 17 th April 2007 Outline Standard LHC Cycle Decay Powering History Other Considerations From Prediction to Optimisation 10/30

12. Nicholas J. SammutFQWG – Decay Prediction and Minimisation During LHC Operation 17 th April 2007 Powering History 11/30

13. Nicholas J. SammutFQWG – Decay Prediction and Minimisation During LHC Operation 17 th April 2007 MB Flat Top Current Dependence effects modelled magnitude of effects 12/30

14. Nicholas J. SammutFQWG – Decay Prediction and Minimisation During LHC Operation 17 th April 2007 MB Flat-Top Time and Pre-inj Time Dependence 13/30

15. Nicholas J. SammutFQWG – Decay Prediction and Minimisation During LHC Operation 17 th April 2007 MB Surface Fit for b3 b1b1 b3b3 b5b5 I FT 0.8350.030.016 t FT -0.02- t preparation -0.07- Median Error 14/30

16. Nicholas J. SammutFQWG – Decay Prediction and Minimisation During LHC Operation 17 th April 2007 Quadrupole Flat-Top Current Dependence MQMQM MQY Preliminary data: only 1 measurement (2 ap) Courtesy S. Sanfilippo, M. Di Castro 15/30

17. Nicholas J. SammutFQWG – Decay Prediction and Minimisation During LHC Operation 17 th April 2007 MQ Flat-Top Time Dependence Preliminary data: only 1 measurement (2 ap) MQ Courtesy S. Sanfilippo, M. Di Castro 16/30

18. Nicholas J. SammutFQWG – Decay Prediction and Minimisation During LHC Operation 17 th April 2007 Pre-cycle Ramp Rate Dependence Measurements to be done on MB,MQ, MQY, MQM (Given low priority) Preliminary data: 4 apertures 17/30

19. Nicholas J. SammutFQWG – Decay Prediction and Minimisation During LHC Operation 17 th April 2007 Outline Standard LHC Cycle Decay Powering History Other Considerations From Prediction to Optimisation 18/30

20. Nicholas J. SammutFQWG – Decay Prediction and Minimisation During LHC Operation 17 th April 2007 o The higher the injection, the lower the decay o Working at 144 A leads to an increase of the b 2 decay amplitude by 14 %. Ap 1 Ap 2 Decay Vs Injection Currents (MQY) Courtesy S. Sanfilippo, M. Di Castro 19/30

21. Nicholas J. SammutFQWG – Decay Prediction and Minimisation During LHC Operation 17 th April 2007 In this current range the variation of the decay amplitude is almost linear. Decay Vs Injection Currents (MQY) Courtesy S. Sanfilippo, M. Di Castro 20/30

22. Nicholas J. SammutFQWG – Decay Prediction and Minimisation During LHC Operation 17 th April 2007 Multiple LHC Cycle Effects Decay time constants show that any history more than 2000s has a negligible effect on decay Maximum difference between two consecutive cycles is 0.05 units for b 3 B 1 difference is less than measurement repeatability Performed on 2 aps 21/30

23. Nicholas J. SammutFQWG – Decay Prediction and Minimisation During LHC Operation 17 th April 2007 Magnet Aging MB1017 - magnetic measurement in April 2003 - magnetic measurement in September 2005  28 months Effect is small within measurement uncertainty but still larger than measurement repeatability Performed on 2 aps 0.07 0.02 0.01 22/30

24. Nicholas J. SammutFQWG – Decay Prediction and Minimisation During LHC Operation 17 th April 2007 Outline Standard LHC Cycle Decay Powering History Other Considerations From Prediction to Optimisation 23/30

25. Nicholas J. SammutFQWG – Decay Prediction and Minimisation During LHC Operation 17 th April 2007 - FIDEL is designed to forecast the harmonics during the LHC cycle within constrained powering scenarios From Prediction to Optimisation - 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. Nicholas J. SammutFQWG – Decay Prediction and Minimisation During LHC Operation 17 th April 2007 Study of Optimisation Cycles t (s) I (A) t (s) 25/30

27. Nicholas J. SammutFQWG – Decay Prediction and Minimisation During LHC Operation 17 th April 2007 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. Nicholas J. SammutFQWG – Decay Prediction and Minimisation During LHC Operation 17 th April 2007 Degaussing Cycles b3-b5 Hall probe 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 Courtesy W. Venturini

29. Nicholas J. SammutFQWG – Decay Prediction and Minimisation During LHC Operation 17 th April 2007 Degaussing Cycles vs Standard LHC Cycle 28/30

30. Nicholas J. SammutFQWG – Decay Prediction and Minimisation During LHC Operation 17 th April 2007 Shift of 0.76 units for b 3 perhaps due to residual magnetisation Degaussing Correlation with Geometric Allowed multipoles are close to the geometric values 29/30

31. Nicholas J. SammutFQWG – Decay Prediction and Minimisation During LHC Operation 17 th April 2007 Discussion 30/30

32. Nicholas J. SammutFQWG – Decay Prediction and Minimisation During LHC Operation 17 th April 2007 Addendum: Rotating Coils 31/30 main field b 1 harmonics uncertainty3 units0.1 units repeatability0.5 units0.01 units main field b 2 harmonics uncertainty5 units0.1 units repeatability1 units0.05 units Dipole Rotating Coils Quadrupole Rotating Coils Quadrupole 5 coils for absolute and compensated measurement Dipole 3 coils for absolute and compensated measurement Ceramic sector of 15m long shaft Precise & integrated over magnet length, but not fast enough for snapback…