LHC Magnets/Splices Consolidation (20 minutes) Francesco Bertinelli 7 June, 2011

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

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

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

4. Need simultaneous presence of two effects: 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 • 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.

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

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

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

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

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

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

11. Shunts on dipole interconnect

12. Shunt description • Copper plate 15 mm wide, 3 mm thick. • Copper annealed at 400⁰ C for 2 hours to maximize RRR Chosen soldered alloy: Sn60-Pb40 for • Melting temperature (<221.15 Sn-Ag) • Wetting capability • Mechanical and electrical properties

13. Shunt work in numbers • 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

14. Copper surface machining

15. The shunt soldering process

16. Insulation box and assembly procedure MB 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) Shunt soldering in position Central insulation piece introduction between the bus bars Lateral insulation pieces introduction Polyimide foil wrapping around insulation pieces 316L collars tie clamping around

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. R_RT-top-side measurement configuration Comsol R_RT-top-side simulation for shunt with defect (courtesy S. Heck)

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) i.e. important to have experienced technicians, specifically for the most critical activities NCR 1002739: Entire cable was squeezed between U-piece and wedge

19. What activities are involved for IC work?

20. Orbital machining to cut open TIG welds

21. Duration of IC work • at 50 IC/week (!!!) for critical activities, • 14 weeks for 1st sector, 5 weeks later for 2nd 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

22. Estimate of IC resources needed 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