Expected Quench Levels of the Machine without Beam: Starting at 7 TeV ? P. Pugnat CERN, Geneva, Switzerland LHC Project Workshop Chamonix XV, Tuesday 24 January 2006

23-27 January 2006Chamonix XV - Expected quench levels of the machine without beam: starting at 7 TeV ? P. Pugnat 2/15 Introduction Abstract (revised) The quench training performance of about 900 LHC main dipoles and 200 main quadrupoles cold tested to date will be presented and commented. From these results an estimate of the number of quenches that could be required to operate the whole machine at nominal energy will be presented without considering beam loss effects. The energy level at which the machine could be operated without being disturbed by training quenches at the early phase of the commissioning will also be addressed. The missing and required information necessary to improve these predictions will be pointed out.

23-27 January 2006Chamonix XV - Expected quench levels of the machine without beam: starting at 7 TeV ? P. Pugnat 3/15 Outline Introduction Quench training performance of MBs –After the 1 st cool-down –After the 2 nd cool-down Extrapolation for the LHC operation –Estimate of the number of Training Quenches of MBs before reaching nominal energy –Estimate of the current level from which Training Quench will occur Case of MQs –Quench training performance –Estimate of the number of Training Quenches before reaching nominal energy –How to improve the reliability of the predictions ? Conclusion

23-27 January 2006Chamonix XV - Expected quench levels of the machine without beam: starting at 7 TeV ? P. Pugnat 4/15 Reminder of the “jargon” used Training Quenches, Detraining, Memory Effect,… Only Training Quenches will be considered; Quench due to cryogenic problem or wrong electrical connections are not considered but can also be present; importance of diagnoses,… No beam. 50 ms/div, 1 mV/div Example of mechanical activity 0.5 s before a quench

23-27 January 2006Chamonix XV - Expected quench levels of the machine without beam: starting at 7 TeV ? P. Pugnat 5/15 Histogram of the number of quenches to reach 8.33 T (11850 A) for the 1 st 908 LHC Main Dipoles cold tested Result on test benches:  38.1 % of MBs reached the nominal field during their 1 st powering without Training Quenches Rejected

23-27 January 2006Chamonix XV - Expected quench levels of the machine without beam: starting at 7 TeV ? P. Pugnat 6/15 Histogram for MBs of the number of quenches to reach 8.33 T (11850 A) after the 2 nd cool down & Direct Extrapolation Rejected TC performed on 115 MBs (  12.7 %); From a direct Extrapolation & the Hypotheses No detraining + MBs with TC will not quench, the number of quenches that can be expected: ( ) x ( x x 0.01)  300 i.e.  40 / octant But problem with the representativity of the sample that contains the weakest MBs, a sort of worst case scenario ?…

23-27 January 2006Chamonix XV - Expected quench levels of the machine without beam: starting at 7 TeV ? P. Pugnat 7/15 Reminder of the Algorithms used for the Cold Test Program From MARIC (streamline of the test program  2 Quench rule) From MARIC (correction the test program proposed by QWU  3 Quench rule)

23-27 January 2006Chamonix XV - Expected quench levels of the machine without beam: starting at 7 TeV ? P. Pugnat 8/15 Extrapolation for the LHC operation MBs Sample bias correction ? From {TC}, the reduction of the average number of quenches to reach ATC 8.33 T is reduced by 82 % ; assuming the same reduction for the sample {NoTC},  Average number of Training Quenches by octant to start at 8.33 T: ( ) x / 8  25 With Hypotheses: No nasty MBs, No Performance Drift for future MBs, No long time Relaxation of the trained magnets, No detraining ?  Estimation for detraining ATC: 0.04 x 3 x 25 < 5 additional Quenches / octant To start at 8.33T, in average a Total Quenches / octant Same approach to estimate the dispersion: 1   6 Training Quenches

23-27 January 2006Chamonix XV - Expected quench levels of the machine without beam: starting at 7 TeV ? P. Pugnat 9/15 Cumulative Statistics for MBs

23-27 January 2006Chamonix XV - Expected quench levels of the machine without beam: starting at 7 TeV ? P. Pugnat 10/15 Training Quench Probability versus B for MBs For field below 7.3 T, Prob {MB-Q}  1% If the field is reduced by 1 T from 8.33 T, Prob {MB-Q}  0.18  0.009

23-27 January 2006Chamonix XV - Expected quench levels of the machine without beam: starting at 7 TeV ? P. Pugnat 11/15 Histogram of the number of quenches to reach A for the 1 st 196 LHC Main Quadrupoles cold tested SSS277 Under investigation Result on test benches:  56.1 % of dipoles reached the nominal field gradient during their 1 st powering without Training Quenches

23-27 January 2006Chamonix XV - Expected quench levels of the machine without beam: starting at 7 TeV ? P. Pugnat 12/15 Case of MQs Poor Statistics for the Memory Effect: –9 SSS with a TC (4.6 %) –ATC, 3/9 quenched above nominal With the same method as for MBs & the same hypotheses: 0.17 x 360  60 Quenches i.e.  8/octant as a very rough estimate due to the lack of data,… As a low Memory Effect was observed on test benches  Some MQs will also exhibit Training Quenches in the tunnel. TCTC {NoTC} # {TC} # 9 # Quench to reach 223 T/m Reduction of 71 % With the same reduction

23-27 January 2006Chamonix XV - Expected quench levels of the machine without beam: starting at 7 TeV ? P. Pugnat 13/15 Conclusion 1/2 From a first estimate & extrapolations of present data, ± 6 Training Quenches/octant for MBs +  8/octant for MQs are expected before to reach the 7 TeV requirements. At the level Proba  few %, Training Quenches will start typically at current value in MBs  11 kA (6.5 TeV) and probably at a close level for MQs. To improve the estimations for MQs, the Memory Effect needs to be study and more statistics is required. When all main magnets will be cold tested, these numbers can be reassessed, octant by octant.

23-27 January 2006Chamonix XV - Expected quench levels of the machine without beam: starting at 7 TeV ? P. Pugnat 14/15 Conclusion 2/2 Expected quench Levels of the Machine without Beam: Starting at 7 TeV ? –It depends on the time available for Training Quenches but this objective should be maintained as much as possible,… –Strategy: Any “spare” time must be dedicated to the training of magnets, all octants in parallel; this is a part of the commissioning.  Dedicated analysis after each Training Quench to give the green light for the next powering; Need of a safe powering flag for each electrical circuit?  Same approach as cold tests on the benches: Postmortem Tools should be available and trained Experts for the analysis. –Training Quenches could arise from magnets other than MBs and MQs but also many other problems to look at before to train the LHC,…

23-27 January 2006Chamonix XV - Expected quench levels of the machine without beam: starting at 7 TeV ? P. Pugnat 15/15 Acknowledgments to The OP Team for providing the results, The EQ Support Team for providing the validation of results, N. Smirnov for providing the statistical results of SSSs, M. Pojer to regularly update statistical results of MBs, A. Siemko for fruitful discussions.