1. LHC Magnets/Splices Consolidation (20 minutes) Francesco Bertinelli 7 June, 2011 23 slides  Status of LHC: electrical connections  Description of shunt consolidation  Quality Control  Scenario for intervention  Missing resources Joint CERN-Pakistan Committee: 6 th meeting

2. LHC electrical interconnections 2 W bellows (see later…)

3. 13 kA (“main”) busbar interconnection splices From L. Rossi, CERN Courier September 2010 3

4. Poor copper to copper continuity. Provided by butt soldered joints, this electrical quality depends on the: -tolerances of the mating surfaces -relative tolerances between 2 paired bus bars -cleaning of the surfaces -capacity of the soldering to fill the gap providing good contact -correct execution of the soldering. Lack of internal contact SC cable to bus bar within the same cross-section: partial melting of the Sn-Ag in the bus bar during connection soldering, loss of solder Need simultaneous presence of two effects: 4

5. 2008-09: new Quench Protection nQPS 5 Our new “eyes” !

6. LHC main IC splices today (SC) From Z. Charifoulline 301 ± 85pΩ R max = 2.7nΩ R max = 3.3nΩ 306 ** ± 313pΩ (**) number of splices in the quads segments corrected, 1.3 added Dipole Buses Quad Buses 12 23 34 45 56 67 78 81 Main Dipoles&Quads Bus, sorted by position, 2048 segments All HWC pyramids and plus ~150 ramps to 3.5TeV analyzed Top 10 Splice Resistances 2nΩ 6

7. Dipole magnets internal splices From R. Principe, A. Zaghloul, P. Fessia 7

8. Dipole internal splices today (SC) From Z. Charifoulline 12 23 34 45 56 67 78 81 3.1±1.2nΩ 8 splices (but not all the same type) 1.4±1.3nΩ 3 + 2* splices (* partially) Main Dipoles Main Quads 8

9. Courtesy R. Flora, C. Scheuerlein (C17-A17)L2 +36μΩ R16→+42μΩ (39.6μΩ, 26.6μΩ) (C30-A30)L2 +36μΩ R16→+29μΩ (41.3μΩ, 12.3μΩ) (B29-A30)R1 +45μΩ R16→+44μΩ (22.8μΩ, 28.5μΩ, 29.9μΩ) (B32-A33)R1 +39μΩ R16→+53μΩ (52.3μΩ, 24.9μΩ, 10.8μΩ) (A18-B17)L2 +35μΩ R16→+17μΩ (28.0μΩ, 11.2μΩ, 13.4μΩ) Biddle measurements: 1-2 main IC splices (NC) 9

10. The estimated R-8/R-16 random error is ±1 µΩ, and the systematic error is about +10 %. R8/R16 test: main IC splices (NC) Courtesy C. Scheuerlein 10

11. Shunts on dipole interconnect 11

12. Chosen soldered alloy: Sn60-Pb40 for – Melting temperature (<221.15 Sn-Ag) – Wetting capability – Mechanical and electrical properties Shunt description  Copper plate 15 mm wide, 3 mm thick.  Copper annealed at 400 ⁰ C for 2 hours to maximize RRR 12

13.  Total magnet to magnet interconnects in the machine: 1 688  Total 13 kA splices: ~10 200  Number of splices to be redone: ~1 500 (15%)  Number of shunts to be applied: ~27 000 Shunt work in numbers 13

14. Copper surface machining 14

15. The shunt soldering process 15

16. Isostatic assembly Mirror symmetry across H and V planes (assembly facilitate and cost saving) Allowed misalignment default V±5 mm, H±3 mm Second insulation skin Pre-stress adjusted with accurate tooling (5kg) Helium ducts in order to give good cooling for the bus bars (no thermal barrier) 1)Shunt soldering in position 2)Central insulation piece introduction between the bus bars 3)Lateral insulation pieces introduction 4)Polyimide foil wrapping around insulation pieces 5)316L collars tie clamping around Insulation box and assembly procedure MB 16

17. Quality Control of main IC splices  R_RT-top-side tests for the QC of individual solder contacts.  After repair the shunt contact on the wedge of M3-QRL-connection, R_RT-top-side is reduced from 10.5 µΩ to 2.1 µΩ. Comsol R_RT-top-side simulation for shunt with defect (courtesy S. Heck) R_RT-top-side measurement configuration 17

18. Examples of damaged cables found in 2009 by the personnel performing the interconnection work NCR 1002739: Entire cable squeezed between U-piece and wedge NCR 990852, 2 strands cut NCR 992513: Cable overheated (>580 °C) NCR 1002739: Entire cable was squeezed between U-piece and wedge 18 i.e. important to have experienced technicians, specifically for the most critical activities

19. What activities are involved for IC work? 19

20. Orbital machining to cut open TIG welds 20

21. Duration of IC work  at 50 IC/week (!!!) for critical activities,  14 weeks for 1 st sector, 5 weeks later for 2 nd sector, 49 weeks for 8 sectors  2 shift work (on different activities), some overlap: 6h–10h/break/11h-15h 12h-16h/break/17h-21h  no learning curve, no built-in contingency, no account for holiday/closure periods  must work sequentially to adjacent sector, without access constraints (i.e. first cool-down and HWC powering)  big concern is the “other activities” to be done in parallel: more realistic is to consider an additional 2-3 months 21

22. Estimate of IC resources needed 22 Pakistan Collaboration?

23. The current scenario  1 “train” only for standard activities  A Special Intervention team to prepare non-standard work before the arrival of the train  Long Shutdown starting January (April?) 2013  Jean-Philippe.Tock@cern.ch to replace F. Bertinelli as IC&Magnet Long Shutdown Project Responsible starting 1 July, 2011 Jean-Philippe.Tock@cern.ch 23