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SMACC ELQC summary

SMACC ELQC summary. S. Heck, C. Scheuerlein, M. Solfaroli, P. Thonet ELQC tests performed by team led by M. Solfaroli LabVIEW data acquisition software by O. Andreassen, EN-ICE-MTA. Outline. ELQC of busbar stabiliser splices Pre-LS1 splices LS1 production splices

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SMACC ELQC summary

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  1. SMACC ELQC summary • S. Heck, C. Scheuerlein, M. Solfaroli, P. Thonet • ELQC tests performed by team led by M. Solfaroli • LabVIEW data acquisition software by O. Andreassen, EN-ICE-MTA

  2. Outline • ELQC of busbar stabiliser splices • Pre-LS1 splices • LS1 production splices • Comparison of 2009 and LS1 R-8 results of the same splices • Machined splices • Consolidated splices • Shunts • DFBA splices • ELQC of insulation boxes • ELQC of disconnected busbar cables C. Scheuerlein, LSC meeting 14.3.2014

  3. What we promised before LS1 C. Scheuerlein, LSC meeting 14.3.2014

  4. The precision of the R-8 test • For estimating the precision of the R-8 test the data set of the consolidated splices that have been produced during LS1 has been used, because for these splices the R-8 variation is expected to be particularly small. R-8 histogram and Gaussian fit of consolidated LS1 production RQ splices. The bin size is 0.1 µΩ, µ=8.84 µΩ, σ=0.31 µΩ, n=1372. C. Scheuerlein, LSC meeting 14.3.2014

  5. Excess resistance overview of pre-LS1 production splices • An overview of the R-8 results is given by sorting the excess resistance values. • Excess resistance is defined as the room temperature resistance difference with respect to the average of a good splice (R-8 minus 5.6 μΩ and R-8 minus 9.3 μΩ for RB and RQ splices, respectively). • Approximately 6% of all excess resistance values exceeded the acceptance threshold value of 5 μΩ (i.e. about 12% of the pre-LS1 splices needed to be repaired because of a too high excess resistance). Excess resistance distribution sorted descending by resistance values. The two highest R-8 excess values of 106 µΩ and 72 µΩ are not shown. C. Scheuerlein, LSC meeting 14.3.2014

  6. Top ten R-8 outliers Highest R-8excess resistance values of RB and RQ splices per sector. C. Scheuerlein, LSC meeting 14.3.2014

  7. Pre-LS1 splice repairs per sector Courtesy M. Solfaroli

  8. R-8 comparison of 2009 production and LS1 production splices • In the first three sectors (56, 67 and 78) LS1 production splices have been controlled directly after repair (before machining). • The average R-8 resistance values obtained for LS1 production RB and RQ splices are 0.12 μΩ and 0.21 μΩ higher than those measured for splices produced during the repair of sector 34 (see EDMS No. 1244158) in 2009, which are considered to be state-of-the-art splices. • The small difference in the average R-8 is at least partly due to the significantly lower temperature in sector 34. The R-8 difference corresponds with a temperature difference of about 5 °C (assuming 20 = 0.0043 K-1 for Cu). • Because of the high quality of LS1 production splices the ELQC step before machining could be stopped, and in the last five sectors the LS1 production splices were first controlled after subsequent machining, and later again after complete consolidation. C. Scheuerlein, LSC meeting 14.3.2014

  9. Comparison of 2009 and LS1 R-8 results • The R-8 test had first been introduced in 2009 during the repair of sector 34. • For 158 (non-consolidated) splices the 2009 R-8 results can be compared with R-8 results measured on the same splices during LS1 after 3 years of LHC operation. R-8 measured in LS1 versus R-8 measured in 2009 C. Scheuerlein, LSC meeting 14.3.2014

  10. Maximum difference R-8LS1 minus R-82009 • In average the LS1 RQ and RB R-8 results are 0.17 μΩ and 0.04 μΩ higher than the 2009 R-8 results for the same splices. • 3 out of the 5 R-8>2 μΩ cases were measured on the two M1 splices of QBQI.34R6. Visual inspection and electrical resistance mapping of these 3 splices did not reveal any signs of splice damage or degradation. There was no R-8 degradation of these 3 splices after machining. • We conclude that there are no indications of a strong R-8 degradation after 3 years of LHC operation. Histogram R-8 (R-8 measured in LS1 minus R-8 measured in 2009) C. Scheuerlein, LSC meeting 14.3.2014

  11. ELQC after splice machining and after consolidation • R-8 measurements have been performed after machining and after complete consolidation. Today almost 99% of all splices have been controlled after consolidation (splices in about 20 interconnects remain to be controlled). • The R-8 acceptance threshold values for machined RB and RQ splices are 10.6 µΩ and 14.3 µΩ, respectively (maximum accepted excess resistance before consolidation is 5 µΩ). • R-8 of about 70 splices increased to an unacceptably high value after machining. These splices were repaired before consolidation. • The R-8 acceptance threshold values for consolidated RB and RQ splices are 6.6 µΩ and 10.3 µΩ, respectively (the maximum accepted splice excess resistance is 1 µΩ). C. Scheuerlein, LSC meeting 14.3.2014

  12. R-8 distribution after machining and after consolidation • After consolidation the average R-8 and the R-8 variance decrease and the R-8 distribution becomes nearly symmetric. R-8 distribution of RB splices after machining and after consolidation (to be updated). R-8 distribution of RQ splices after machining and after consolidation (to be updated). C. Scheuerlein, LSC meeting 14.3.2014

  13. R-8 decrease after application of shunts • After application of shunts R-8RQ and R-8RB values decrease in average by 1.34 µΩ and 0.93 µΩ, respectively. • The calculated R-8 decrease after shunting due to the additional splice cross section is -1.35 µΩ and -0.80 µΩ for RQ and RB splices,respectively. • The lowest average R-8 is obtained in sector 34 (average R-8RQ and R-8RB of consolidated splices in sector 34 is 0.23 µΩ and 0.17 µΩ lower than the average in sectors 56, 67 and 78. Average R-8 before and after application of shunts on RQ and RB splices. C. Scheuerlein, LSC meeting 14.3.2014

  14. Can we estimate the busbar temperature differences in the different LHC sectors from R-8? Estimation of the busbar temperature difference ΔT with respect to the busbar temperature in sector 34 (assuming 20 = 0.0043 K-1 for Cu) C. Scheuerlein, LSC meeting 14.3.2014

  15. ELQC of shunts R-top-side measurement configuration and FE model with surface electric potential. • An independent quality control of the shunts was needed in order to guarantee that the shunts can provide a redundant current path. • Direct current electrical resistance mapping (the so-called R-top-side test) has been used to control each of the about 27000 shunt solder contacts. Different methods that have been considered for the shunt NDT (from 2nd LHC splice review). C. Scheuerlein, LSC meeting 14.3.2014

  16. The only real R-top-side outlier From “Quality control of the main interconnection splices before and after consolidation” presentation at the 2nd LHC splice review-28 Nov. 2011 C. Scheuerlein, LSC meeting 14.3.2014

  17. Comparison of the average R-top-side resistance in the different sectors • The average R-top side values are 1.26±0.34 µΩ and 1.03±0.34 µΩ for RQ and RB shunts, respectively (average results of about 55000 R-top-side results for each shunt type). • Only few non-conform shunts were detected. No real R-top-side outlier was found in the LHC (the maximum R-top-side measured in the LHC was <3 µΩ, and after re-heating the shunt was reduced below the acceptance threshold. Average R-top-side results for RQ and RB shunts in the different LHC sectors C. Scheuerlein, LSC meeting 14.3.2014

  18. Comparison of the R-top-side resistance of the different shunts • The constant R-top-side results confirm the high quality of the solder contacts at all shunt positions across the entire LHC. RQ acceptance threshold 1.9 µΩ RB acceptance threshold 1.7 µΩ R-top-side average values sorted for the different shunt positions per LHC sector. Courtesy M. Zinser. C. Scheuerlein, LSC meeting 14.3.2014

  19. ELQC of DFBA splices • Pigtail splices • All pigtail splice controls are finished. • The maximum excess resistance of all pre-LS1 pigtail splices was <3 µΩ. • Before consolidation 6 pigtail splices were repaired because it was not possible to machine smooth surfaces to apply the side shunts. • SHM splices • All SHM splice controls after machining are completed, for 12 consolidated SHM splices ELQC remains to be done. • 1 out 50 pre-LS1 SHM splices that were controlled before machining had an excess resistance >5 µΩ (a RQ splice with Rexcess=17.3 µΩ) • Several SHM splices were repaired for geometrical reasons, or because R-8 increased strongly during machining. C. Scheuerlein, LSC meeting 14.3.2014

  20. ELQC of insulation boxes • A visual control of all completely assembled insulation boxes is done by the ELQC team according to test procedure EDMS No. 1240302. • Today a visual control of almost 90% of the insulation boxes has been performed. • Most non-conformities were related to the centering of the boxes, and initially to boxes without additional Kapton insulation in contact with the flanges. C. Scheuerlein, LSC meeting 14.3.2014

  21. Visual control of disconnected busbar cables • The ELQC team performed avisual control of all disconnected cables (about 6000) after cable pre-tinning (“stabilisation”). • The main cable defect types found (cut strands and overheated cables) had been anticipated. • Because of the absence of a non-destructive quantitative in situ test, the control of cables cannot be as meaningful as that of the busbar stabiliser splices. • Most cables with signs of overheating had already been detected by the LMF-QA team, directly after splice opening and before pre-tinning. C. Scheuerlein, LSC meeting 14.3.2014

  22. The limits of a visual cable control at the example of the overheated cable QBBI.B21R4-M1-Ext-L (NCR 1351033) • The extremity of QBBI.B21R4-M1-Ext-Left is one of the most obviously degraded cables found in LS1. • Magnetisation measurements confirm cable overheating at the cable extremity and cable center. • After stabilisation it is not obvious to observe even this extreme degradation anymore. • The splice is foreseen for a special repair. Magnetisation measurements courtesy C. Senatore, University of Geneva. QBBI.B21R4-M1-Ext-Left before stabilisation QBBI.B21R4-M1-Ext-Left after stabilisation C. Scheuerlein, LSC meeting 14.3.2014

  23. Visual control of cables in 1.9 K resistance outlier segments • All splices in 1.9 K resistance outlier segments (outlier is defined as Rmax-1.9 K>0.82 nΩ for RB and Rmax-1.9 K>2.0 nΩ for RQ splices) were opened and a visual cable control was performed by the ELQC team before stabilisation. • In some cases strong splice overheating was the reason for the increased 1.9 K resistance (as confirmed by magnetisation measurements of extracted strand samples). • In some high resistance segments no cables with obvious defects were found. • 14 splices have been selected for which degraded cables are removed and replaced by new cable splices. C. Scheuerlein, LSC meeting 14.3.2014

  24. Overheated splices selected for special repair with new cable splices • QBBI.A21L6-M2-Int, NCR 1290623, repair is completed. • QBBI.B34L3-M2-Ext, NCR 1329755, repair is completed. • QBQI.17R2-M1-Ext, NCR 1325832, repair is completed. • QBQI.17R2-M2-Int, NCR 1325832, repair is completed. • QBQI.18R8-M2-Ext, NCR 1335759, repair is completed. • QBQI.19R2-M2-Ext, NCR 1326003, repair is completed. • QQBI.24R2-M3-Int, NCR 1326308, repair is completed. • QBQI.14L3-M3-Ext, NCR 1303387, repair is completed. • QQBI.19L4-M3-Ext, NCR 1310422, to be repaired. • QBBI.A31L4-M3-Ext, NCR 1310420, to be repaired. • QBQI.16L4-M3-Ext, NCR 1346352, to be repaired. • QBQI.26L4-M1-Ext, NCR 1346335, to be repaired. • QBBI.B21R4-M1-Ext, NCR 1351033, to be repaired. • QBQI.12L5-M1-Int, NCR 1358325, to be repaired. • QBBI.B13L5-M3-Ext, NCR 1360798, to be decided if special repair is needed. C. Scheuerlein, LSC meeting 14.3.2014

  25. Possible influence of splice opening and re-connection on the future 1.9 K splice resistance • Splice opening and re-connection invariably causes a slight cable degradation and risks cable damage. • Thus, after the re-connection of 3000 splices the future 1.9 K segment resistance results may show a bit higher resistances as those measured before LS1. • Single cut strands are not causing a measurable resistance increase. • Overheated cables could cause a measurable resistance increase in the order of nΩ. C. Scheuerlein, LSC meeting 14.3.2014

  26. Conclusion-ELQC of busbarstabilisers • Each of the about 10000 active main interconnection splice has been controlled by the ELQC team before, during and after completion of the consolidation process. • About 30% of all pre-LS1 splices needed to be completely redone before they could be consolidated (mainly because they had an excess resistance >5 µΩ, or because of geometrical distortions that did not allow application of shunts or the insulation box). • Before LS1 the highest excess resistances of RB and RQ splices were 71.9 μΩ and 107 μΩ, respectively (corresponding with a non-stabilised busbar cable length of 5.4 cm and 8.1 cm). • After splice repairs and machining the maximum excess resistance was already reduced to 5 µΩ. • After consolidation the maximum excess resistance of all active main interconnection splices in the LHC is reduced by two orders of magnitude (highest excess resistance is now 1 µΩ). • Due to the additional shunt Cu cross section, in average the main interconnection splice resistance is now lower than that of a continuous busbar. C. Scheuerlein, LSC meeting 14.3.2014

  27. Conclusion-ELQC of the shunt solder contacts • Each of the about 27000 shunt solder contacts has been controlled by the ELQC team. • Thanks to the very sophisticated soldering process and procedures and the high quality of production only few non-conform shunts were detected. • No single R-top-side outlier comparable to that found during the Q8-Q9 validation test was detected during LS1. • All the shunts on the LHC main interconnection splices provide a redundant current path. C. Scheuerlein, LSC meeting 14.3.2014

  28. ELQC of busbar cable splices-conclusion and outlook • A visual control of the about 6000 disconnected cables after stabilisation has been performed by the ELQC team. • A visual cable control is not a guarantee the all re-connected cable splices will be perfect. After re-connection of 3000 cable splices the future 1.9 K resistance results maybe slightly higher then they were before LS1. • Disconnection and re-connection of a large number of cable splices is possible because of the huge margin in terms of critical current density and mechanical strength of the Nb-Ti alloy superconductor. • All future superconductors beyond Nb-Ti will have either much less margin in mechanical properties or/and in critical current density. C. Scheuerlein, LSC meeting 14.3.2014

  29. Acknowledgements Many, many thanks to Matteo’s team! C. Scheuerlein, LSC meeting 14.3.2014

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