Other arguments to train two sectors to 7 TeV Arjan Verweij, TE-MPE-PE Draft version. Numbers and conclusions open for discussion you can't know where you're going until you know where you've been A. Verweij, QBT, 12/7/2016

Questions: Is the increased training limited to a series of 3xxx magnets or not? Another part of the 3xxx production could start increased training above 6.5 TeV. Will (part of) the 1xxx and 2xxx production also start increased training above 6.5 TeV, similar to part of the 3xxx production? Will the sub-second quench propagation, as observed in about 30% of the quenches above 10.7 kA, become more and more frequent at higher currents? This could slow down the cryogenic recovery significantly, and hence increase the time needed for training. This fast propagation could be reduced by increasing QPS thresholds, but such a change requires a dedicated preparation. Will there be any other unforeseen effects/showstoppers between 6.5 and 7 TeV? Is there a difference for the re-training (or memory) between a “fast” thermal cycle (typically up to a few weeks, and a “long” thermal cycle (typically 1 year)? A. Verweij, QBT, 12/7/2016

Should we also train the RQD/F to 7 TeV? Questions: Should we also train the RQD/F to 7 TeV? Do we take the same margin (100 A) for training to 7 TeV or slightly more? After the training, should we do a long plateau at 7 TeV of about 20 hrs? To answer some of these questions we should not only focus on the 3xxx magnets, but try to test a as-uniform-as-possible share of the three manufacturers along their production. We only focus on the combinations 12+45, 23+45 and 34+45 since the other ones have a much larger number of foreseen quenches. A. Verweij, QBT, 12/7/2016

#Mag in LHC #Q in LHC #Q/#Mag in LHC (%) #Mag in S45 #Q in S45 #Mag in S12&S45 #Mag in S23&S45 #Mag in S34&S45 10xx 89 2 1 4 16 11xx 97 18 26 37 12xx 29 35 39 13/4xx 117 43 20xx 94 19 8 25 21xx 7 38 3 53 72 22xx 98 6 17 20 9 23/4xx 134 82 21 30xx 10 31xx 99 49 24 42 32xx 100 44 34 22 33/4xx 116 11 23 & 45 gives the best distribution; 34 & 45 is also quite good especially due to the larger number of 20xx magnets (which quenched quite a bit up to 6.5 TeV) A. Verweij, QBT, 12/7/2016

Risks Situation: Dipole quenches in SM18 during the reception tests: 5123 Cool-down 1: 4593 Cool-down 2: 377 Cool-down 3: 122 Cool-down 4: 20 Cool-down 5: 11 Dipole training quenches in the LHC: about 210 Secondary quenches: about 800 Expected number of quenches for training one sector: about 30-40 quenches and 120-160 secondary quenches. A. Verweij, QBT, 12/7/2016

Risks Quench heater damage. We had 4 QH problems before LS1. In all cases the HF QH was substituted by a LF QH during operation and the magnet was replaced during LS1. We have up to now 3 QH problems after LS1. In these 3 cases the HF QH has been substituted by a LF QH. Magnets concerned: B16R2, B24L5, A26R8. The remaining heaters of these 3 magnets are probably more prone to damage. We have never observed in the LHC a heater damage that caused an inter-turn short or coil-to-ground failure. It seems that heater damage is more related to thermal cycling than to quenching. Conclusion: possibility of QH damage is not negligible but consequences are expected to be minor. A. Verweij, QBT, 12/7/2016

Risks Short-to-ground Shorts-to-ground have occurred in the RB circuits in the warm leads, in the lyra, and in the diode container. Short-to-grounds in the warm leads and the lyra seem to be related to the powering but have no correlation to quenches. Shorts-to-ground in the diode container might be triggered by the movement of metallic debris in the container or towards the half-moon connection due to the helium flow during a quench. Such a short has been observed once and the short was burned away afterwards. There is however a possibility that this remedy will not always work. Single short-to-grounds should not give collateral damage. Multiple short-to-grounds might cause additional damage, depending on the position of the shorts and the occurrence during the quench event. A. Verweij, QBT, 12/7/2016

Risks Damage due to helium pressure shock wave The fast helium pressure transients are about 12 bar (with slower increase up to 18 bar). This could create damage to the (kapton) insulation if not properly fixed to the conductor, hence possibly creating a short-to-ground. Consequences might be large. Damage to auxiliary equipment due to high voltage Even though all equipment is ELQA tested up to about 2 kV, this could still happen since some components might experience fatigue effects. Consequences are expected to be minor. Coil-to-ground failure and Inter-turn short Both defects have never occurred in the LHC. The consequence of such defects are large: warm-up + replacement of the magnet + cool-down + ELQA + recommissioning. Estimated to be about 3 months. A. Verweij, QBT, 12/7/2016

Risks Diode problem Failure of the diode or excessive heating in a contact in the diode pack might require exchange of a diode. This has never happened in the LHC. Consequences are large: warm-up + replacement of the diode + cool-down + ELQA + recommissioning. Estimated to be about 3 months. Opening/arcing of the bypass bus Similar to the 2008 accident. This probability is extremely small since all joints have been inspected, repaired, and shunted. Furthermore the CSCM test has been performed in each sector, and the splices are continuously monitored. The consequences can be huge. Damage to the 13 kA energy extraction switches Frequent switching could require maintenance of the switches. Consequences are minor A. Verweij, QBT, 12/7/2016

Frequency (per quench event) Risks Damage Frequency (per quench event) Conse-quences Risk for 30 quenches Damage that can be repaired without warm-up Quench heater failure without collateral damage 0.001 1 d 0.03 d Damage to aux. equipment Damage to the 13 kA EE switches 0.01 0.3 d Single short-to-ground in the cold part, which can be repaired (burnt-out) 0.005 2 d Damage requiring warm up and replacement of (part of) a cold-mass Quench heater failure causing coil-to-ground or inter-turn short 0.0001 100 d Single short-to-ground in the cold part, which requires cold-mass replacement 3 d Damage to the helium pressure shock wave requiring cold-mass replacement Coil-to-ground or inter-turn short Diode damage Damage not limited to one cold-mass Double short-to-ground (worst case) 0.00001 300 d 0.1 d Opening/arcing of the bypass bus A. Verweij, QBT, 12/7/2016