Report on the 2009 LHC Performance Workshop at Chamonix

1. Report on the 2009LHC Performance Workshop at Chamonix Eric Prebys APC/LARP The truth is out there!

2. Scope of the workshop • The primary goal of this workshop was to provide the CERN Directorate with information and recommendations to define the scope of activities and final schedule and plan 2009/2010 running of the LHC. • This planning is obviously dominated by the consequences incident of September 19. • Questions about how this incident occurred were examined to the extent that they impact repair and remediation; however, questions regarding the decision process that allowed to occur were deferred to the external review committee. E. Prebys, AEM

3. Key questions going into the workshop • When will the LHC start up? • The DG has made a strong commitment to a physics run of the LHC “in 2009”, provided it does not threaten the long term viability of the accelerator. • Run through the winter? • How much does this cost? • How many sectors to warm up? • There are currently four sectors warm, and a plan to install new pressure relief flanges with dramatically increased capacity. • To install these new relief flanges on the remaining four sectors would require a warm up, which has it’s own risks and scheduling headaches. • The baseline plan is to leave the remaining sectors cold, and effect an intermediate pressure relief enhancement by replacing clamps with springs on a number of existing flanges. • Energy • Quickly became clear the options were 4 or 5 TeV/beam. E. Prebys, AEM

4. Chamonix Presentations • After the close of the meeting, Steve Myers made all the workshop talks public on the CERN Indico site, which you can access with this shortcut: • http://tinyurl.com/Chamonix2009 • Of particular interest is Steve’s summary talk at the end • (very) Partial glossary of terms: • “Consolidation” – CERNglish word referring to a set of actions and/or repairs to address known shortcomings of a system. • “MLI” – multi-layer insulation, which was blown all over the tunnel and sucked into the beam pipe • “DN200” – 200 mm pressure relief flange (“bandaid du jour”). • “QPS” – quench protection system • “MCI” – maximum credible incident E. Prebys, AEM

5. Incident on September 19th* • On September 19th, sector 3-4 was being ramped to 9.3 kA, the equivalent of 5.5 TeV • All other sectors had already been ramped to this level • Sector 3-4 had previously only been ramped to 7 kA (4.1 TeV) • At 11:18AM, a quench developed in the splice between dipole C24 and quadrupole Q24 • Not initially detected by quench protection circuit • Power supply tripped at .46 sec • Discharge switches activated at .86 sec • Within the first second, and arc formed at the site of the quench • Helium pressure rose beyond .13 MPa and ruptured into the insulation vacuum. • Vacuum also degraded in the beam pipe • The pressure at the vacuum barrier reached ~10 bar (design value 1.5 bar). The force was transferred to the magnet stands, which broke. *see talk by Philippe LeBrun, Monday AM E. Prebys, AEM

6. Stand failure (designed for 1.5 bar max)* • Incident on 19th of September 2008 => failure of some supports of SSS in sector 3-4 due to longitudinal loads *O. Capatina, Tuesday PM E. Prebys, AEM

7. It could have been worse* • Under the rules at the time, there could have been people in adjacent sectors or service areas, who might have been killed or seriously hurt. • It could have occurred in, eg, the dispersion suppression (DS) region, for which spares would have been an issue. • It could have happened in the triplet (which BTW has much better designed joints), and damaged the experiments. • If the arc had cut into both He lines, it would have been 40 kg/s of He, a factor of 20 over design • This MCI drives the new pressure relief specification *see talk Jim Strait, Wednesday PM E. Prebys, AEM

8. Important questions about Sept. 19 • Why did the joint fail? • Quality control problems • Inherent weakness in joint design (no clamps) • Why wasn’t it detected in time? • There was indirect (calorimetric) evidence of an ohmic heat loss, but these data were not routinely monitored • The bus quench protection circuit had a threshold of 1V, a factor of ~1000 too high to detect the quench in time. • Why did it do so much damage? • The pressure relief system was designed around an MCI Helium release of 2 kg/s, a factor of ten below what occurred. E. Prebys, AEM

9. Electrical joint in 12 kA bus bar* *see talk by Arjan Verweij, Tuesday PM E. Prebys, AEM

10. No electrical contact between wedge and U-profile with the bus on at least 1 side of the joint No bonding at joint with the U-profile and the wedge What happened? Theory: A resistive joint of about 220 n with bad electrical and thermal contacts with the stabilizer • Loss of clamping pressure on the joint, and between joint and stabilizer • Degradation of transverse contact between superconducting cable and stabilizer • Interruption of longitudinal electrical continuity in stabilizer Problem: this is where the evidence used to be A. Verweij E. Prebys, AEM

11. Addressing problems • Use calorimetric data to find suspicious joints, then check with precision resistance measurements: • 1 sigma = 20 nOhms (design value .6 nOhm) • Thermal runaway @ ~85 nOhms @ 5TeV • Two additional bad joints found, both of them inside magnets, which were removed. • All new joints photographed and check with ultrasound. BAD GOOD E. Prebys, AEM

12. Calorimetric Data* Smoking gun? S1-2 S2-3 S3-4 S4-5 +40 mK 7 kA 7 kA 7 kA 9.3 kA Relative temp -10 mK 1-2 hour flat tops S5-6 S6-7 S7-8 S8-1 +40 mK 7 kA 7 kA 8.5 kA 7 kA Relative temp -10 mK In the future, calorimetric data will be routinely monitored *See talk by Nuria Catalan Lasheras, Monday AM E. Prebys, AEM 6 February 2009

13. Improved quench protection* • Old quench protection circuit triggered at 1V on bus. • New QPS triggers at .3 mV • Factor of 3000 • Should be sensitive down to 25 nOhms (thermal runaway at 7 TeV) • Can measure resistences to <1 nOhm • Concurrently installing improved quench protection for “symmetric quenches” • A problem found before September 19th • Worrisome at >4 TeV *See talks by Arjan Verveij and Reiner Denz, Tuesday PM E. Prebys, AEM

14. Improved pressure relief* New configuration on cold sectors: Turn several existing flanges into pressure reliefs (while cold). Also reinforce stands to hold ~3 bar New configuration on warm sectors: new flanges (12 DN200 + 8 DN100) (DP: Design Pressure) *Vittorio Parma and Ofelia Capatina, Tuesday PM L. Tavian E. Prebys, AEM

15. Replacement of magnets* • 15 SSS (MQ) • 1 not removed (Q19) • 14 removed • 8 cold mass revamped (old CM, partial de-cryostating for cleaning and careful inspection of supports and other components) • 6 new CMs • In this breakdown there is consideration about timing (SSS cryostating tales long time; variants problems). • 42 Dipoles (MBs) • 3 not removed (A209,B20,C20) • 39 removed • 9 Re-used (old CM, no decryostating –except one?) • 30 new CMs • New cold masses are much faster to prepare than rescuing doubtful dipoles) *Lucio Rossi (magnets) and Francesco Bertinelli (connections), Tues AM E. Prebys, AEM

16. Cleaning vacuum lines* • Most dirty beam pipes in removed magnets • Several must be cleaned in tunnel • Soot: successive passes with wet and dry sponges • MLI: little vacuum cleaner *Vincent Baglin, Tuesday AM E. Prebys, AEM

17. Status and schedule* • Magnet reinstallation begins this week. • Work on flanges begins in a few weeks. • Decision of Directorate (announced today) • Do NOT warm up remaining four sectors • Start up in late September, collisions in late October • Run through winter until next fall (with short break for Christmas, of course) • Raise energy to 5 TeV as soon as safe (symmetric QPS?) • Collect ~200 pb-1 at 5+5 • 200 pb-1 @ 5+5 TeV ~ Tevatron Run II so far • Possible ion run at the end *See Friday talks, particularly Steve Myers’ summary E. Prebys, AEM

18. Besides that, Mrs. Lincoln, how was the play?* • We shouldn’t forget how incredibly well things were going before the incident. • Beam was circulated in both directions within a few hours • Beam was captured within a day • Optics measurements uncovered a few minor wiring problems. Right Wrong *Thursday AM E. Prebys, AEM

19. Going beyond 5 TeV* • Will NOT happen this year • Problem with dipoles “forgetting their training” after the period of storage • Only occurs with one out of the three vendors (Noel) • This was discovered before the turn on • Project LOTS of quenches to go beyond 6 TeV • 6.5 TeV: ~10 per sector • 7.0 TeV: ~100 per sector • Can only do 2-3 quenches/day • 1 to 2 months of quenching to get to 7 TeV • Risk of damage? *Arjan Verveij, Monday AM and Ezio Todesco, Thursday PM E. Prebys, AEM