Quench behavior of the main dipole magnets in the LHC By Gerard Willering, TE-MSC On behalf of the MP3-CCC team Acknowledgements TE-MSC, MP3, BE-OP, TE-MPE, TE-EPC, EN-ICE Commissioning the magnet circuits in the LHC is only the final stage before operation. The results shown in this presentation reflect the accomplishment of many teams and persons involved. LMC, Quench behavior of the main dipole magnets in the LHC, LMC , by Gerard Willering 2

Contents Introduction Powering history Magnet training single magnets HWC campaign main dipoles in the LHC HWC 2015 Statistics for LHC, per sector and per firm Comparison with Comparison with production and acceptance tests. Outlook Quenches during 6.5 TeV operation run 2 Predictability of reaching 7 TeV Quench behavior of the main dipole magnets in the LHC, LMC , by Gerard Willering 3

Contents Introduction Powering history Magnet training single magnets HWC campaign main dipoles in the LHC HWC 2015 Statistics for LHC, per sector and per firm Comparison with Comparison with production and acceptance tests. Outlook Quenches during 6.5 TeV operation run 2 Predictability of reaching 7 TeV Quench behavior of the main dipole magnets in the LHC, LMC , by Gerard Willering 4

Introduction - Powering history of the main dipole magnets in the LHC magnets + spares produced by 3 firms 62 % tested to kA 38 % between 12 and kA About 10 % had a thermal cycle including training Run 1 Operation up to 6.7 kA LS1 All magnets warmed up HWC 2015 Training up to kA Run 2 Operation up to kA Since reception tests only 1 sector was trained to above 10.3 kA until the recent HWC campaign. Quench behavior of the main dipole magnets in the LHC, LMC , by Gerard Willering 5 HWC 2008: up to 9.3 kA S56: 11.2 kA S45: 10.3 kA

Introduction - Magnet training of single magnets in the SM18 test facility Training: The magnet quenches at a higher current then before. Detraining: The magnet quenches at a lower current then before. Memory: After a thermal cycle less training quenches are needed to reach the same current. 120 out of 1232 magnets in the LHC had a thermal cycle with training as part of the reception tests.. MB magnets have shown memory effect after thermal cycle. Firm 3 magnets are known to have less memory than firm 1 and 2 magnets. Fraction of magnets with minimum one quench below kA Virgin run SM18 Second cooldown in SM18 In the LHC in HWC 2015 All See slide 11 Firm See slide 11 Firm See slide 11 Firm See slide 11 Quench behavior of the main dipole magnets in the LHC, LMC , by Gerard Willering 6 Training Detraining Memory

Introduction - Dipole circuit HWC campaign 2015 Powering procedures EDMS Quench behavior of the main dipole magnets in the LHC, LMC , by Gerard Willering 7 8 RB circuits with 154 magnets powered in series. Nominal current 6.5 TeV: A. Magnet training current: A (equals 6.55 TeV) Training quenches: most quenches occur during the training cycle Flattop quenches: some quenches occur during the flattop cycles. Training cycle Flattop cycle

Introduction - Quench event during HWC in the LHC Example of a quench event in S81 in the magnet in position C30 B30C30A30 Q28 B31A31 Q29 56 s65 s 82 s88 s Quench behavior of the main dipole magnets in the LHC, LMC , by Gerard Willering 8  154 magnets in series  Quench in a magnet triggers energy extraction opening. Current in the circuit decays exponentially with τ = 100 s.  Negative inductive voltage across each superconducting magnet.  Positive voltage across quenched magnet when current goes through bypass diode. Typically a training quench is followed by secondary quenches through heat propagation.

Quench behavior of the main dipole magnets in the LHC, LMC , by Gerard Willering 9 Quench causes#Average current (kA) Training and flattop quenches Thermal propation quench ElectroMagnetic coupling iQPS Electromagnetic coupling nQPS Others25 Topic was discussed in LMC, S. Le Naour, Improved by increase of nQPS threshold from 400 to 500 mV (EDMS ) At 400 mV: 5 trips in 25 quenches At 500 mV: 6 trips in 154 quenches Each quench will give some electrical, thermal and mechanical stress. Strategy is to limit the number of quenches and Quench Heater firing as much as possible. Total # of Quench Heater firings while powering the magnets > 750 magnets.  2015: 2 quench heater circuit failures  4 dipoles were replaced in LS1 due to quench heater failure.  1 short circuit occurred in the cold mass during quench tests. Focus in this presentation on training and flattop quenches. Introduction - Secondary quenches B30C30A30 Q28 B31A31 Q29 56 s65 s 82 s88 s

Contents Introduction Powering history Magnet training single magnets HWC campaign main dipoles in the LHC HWC 2015 Quench statistics for LHC, per sector and per firm Comparison with production and acceptance tests. Comparison with Outlook Quenches during 6.5 TeV operation run 2 Predictability of reaching 7 TeV Quench behavior of the main dipole magnets in the LHC, LMC , by Gerard Willering 10

During the whole campaign 179 MB quenches recorded Manufacturer# magnets that quenched once # magnets that quenched twice # magnets that quenched 3 times Total # quenches Firm 1 (400)5005 Firm 2 (420)2700 Firm 3 (412) All (1232) Now we can complete the table from slide 6 HWC 2015 – Quench overview Fraction of magnets with minimum one quench below kA during training cycle. Manufact urer Virgin run SM18 (no thermal cycle) Second cooldown SM18 In the LHC in 2015 Firm (5/400) Firm (24/420) Firm (131/412) All Slightly worse than second cooldown Significantly worse than second cooldown. Quench behavior of the main dipole magnets in the LHC, LMC , by Gerard Willering magnets did not quench, 168 did quench.

HWC 2015 – Quenches per sector Sector# Training quench Flattop quenches S1270 S23170 S34151 S45510 S56183 S67221 S78193 S81290 Total1718 Large variation in number of training quenches per sector, between 7 and 51 quenches! Quench behavior of the main dipole magnets in the LHC, LMC , by Gerard Willering 12 TrainingFlattop All flattop quenches occured within a small margin from the training current. In the following part of the presentation they are included in the quench statistics.

HWC 2015 – All 2015 quenches in one figure. Naming example: MB 2029 Firm 2, series number 29. More details per firm in the next 3 slides Quench behavior of the main dipole magnets in the LHC, LMC , by Gerard Willering 13

HWC 2015 – Quenches in Firm 1 magnets Circuit #Magnets installed# Quench Average number of quenches per magnet RB.A RB.A RB.A RB.A RB.A RB.A RB.A RB.A  Only 5 quenches  Spread over the whole series.  Spread over the sectors Quench behavior of the main dipole magnets in the LHC, LMC , by Gerard Willering 14

HWC 2015 – Quenches in Firm 2 magnets Circuit #Magnets installed# Quench Average number of quenches per magnet RB.A RB.A RB.A RB.A RB.A RB.A RB.A RB.A Quench behavior of the main dipole magnets in the LHC, LMC , by Gerard Willering 15  27 quenches  Higher probability in earlier part of the series  Higher number of quenches in S78.  First batch of magnets installed in S78.

HWC 2015 – Quenches in Firm 3 magnets Circuit #Magnets installed# Quench Average number of quenches per magnet RB.A RB.A RB.A RB.A RB.A RB.A RB.A RB.A Much higher number of firm 3 quenches in S45. Much lower number of firm 3 quenches in S78. Quench behavior of the main dipole magnets in the LHC, LMC , by Gerard Willering 16  147 quenches  Not evenly distributed over the serial number of the magnets.

HWC 2015 – Firm 3 magnet distribution and quench probability Quench behavior of the main dipole magnets in the LHC, LMC , by Gerard Willering 17 Note: We are not certain that differences in production are the cause of the higher quench probability. More investigation is needed to exclude differences in transport, installation, storage, etc. for the different sectors.

HWC 2015 – Comparison with quenches up to kA during reception tests  Only first quench from reception test considered.  No direct correlation between 2015 and reception tests.  For certain batches the number of quenched magnets is higher in 2015 than during the first reception tests. Quench behavior of the main dipole magnets in the LHC, LMC , by Gerard Willering 18 Deeper investigation needed for clear conclusions.

HWC 2015 – Correlation to thermal cycles during reception test 10 % of the magnets had a thermal cycle. The slowest training magnets were selected for the thermal cycle, hence the magnets with the thermal cycle had the most quenches. The significance and mechanism of a correlation is under investigation. Quench behavior of the main dipole magnets in the LHC, LMC , by Gerard Willering 19 # Magnets in the LHC # Magnets quenched in 2015 Fraction of quenched magnets in LHC Average number of quenches in acceptance tests Magnets single training >12 kA Magnets with thermal cycle and second training to > 12 kA Total

HWC Comparison training in 2008 with  30 quenches up to kA in 2008  15 detraining quenches (training cycle)  Maximum detraining 670 A  Shorter training to the same current.  3 quenches up to kA in 2008  11 detraining quenches  Maximum detraining 430 A  Longer training to the same current Quench behavior of the main dipole magnets in the LHC, LMC , by Gerard Willering 20 S45S56

Contents Introduction Powering history Magnet training single magnets HWC campaign main dipoles in the LHC HWC 2015 Statistics for LHC, per sector and per firm Comparison with Comparison with production and acceptance tests. Outlook Quenches during 6.5 TeV operation run 2 Predictability of reaching 7 TeV Quench behavior of the main dipole magnets in the LHC, LMC , by Gerard Willering 21

Outlook - Flattop quenches during Run 2 From the 8 quenches after the completion of the training cycle:  6 flattop quenches at training current level.  2 quenches at flattop cycle within the first minutes at nominal current. Quench behavior of the main dipole magnets in the LHC, LMC , by Gerard Willering 22  So far the 8 sectors combined have spent 577 hours at ≥ nominal current and 27 hours at training current.  One LHC year accounts for about hours in the 8 circuits combined.  The 2 quenches at nominal current occured in the first minutes. Mechanism and probability of detraining unknown: No prediction possible.

Outlook - Expectations training to 7 TeV Mechanisms for (de-)training, long term effects, thermal cycles, etc. need to be better understood, also with respect to the various batches of magnets. Further investigation and a training to 7 TeV of at least one sector is needed to make a good prediction. Chamonix 2009 E. Todesco Chamonix 2009 A. Verweij LHC TeV TeV TeV-900 Predictions are only as good as the assumptions, which in turn relies on available knowledge. Earlier predictions were done in Chamonix 2009, based on HWC The reality in 2015 is that the number of quenches is higher than expected. Note that the 10 % of magnets that had a thermal cycle were slowest training magnet, with the highest number of quenches. Note that the LHC curve is dominated by a batch of the magnets, while the SM18 data is more homogeneous quench data for all magnets. Different phenomena may apply, slope of the curve may change. Quench behavior of the main dipole magnets in the LHC, LMC , by Gerard Willering 23 Good prediction needs more time.

 The 8 main dipole circuits have been trained up to 6.55 TeV equivalent current.  1064 magnets did not quench!  A total of 179 quenches has been recorded in 168 magnets.  The detraining as observed in S56 in 2008 is confirmed in other sectors.  Significant differences in the training behavior in different sectors and different batches of magnets have been observed. What do we still need to understand?  The mechanism of the detraining over time.  Probability and mechanism of flattop quenches during operation.  Training beyond 6.55 TeV. Followup  End of HWC marks a restart for investigation on magnet training behavior  Investigations of the mechanisms of detraining over time, after thermal cycles and semi-continuous powering.  Investigation if changes in magnet production, storage, treatment, transport, installation, testing, etc. can be correlated to training quench behavior. This may be important for future magnet development and production. Summary slide Quench behavior of the main dipole magnets in the LHC, LMC , by Gerard Willering 24

For a good understanding on main dipole quenches and predictions I recommend to read: C. Lorin, A. Siemko, E. Todesco, and A. Verweij. "Predicting the quench behavior of the LHC dipoles during commissioning." Applied Superconductivity, IEEE Transactions on 20, no. 3 (2010): cds record Quench behavior of the main dipole magnets in the LHC, LMC , by Gerard Willering 25

Extra Slides Quench behavior of the main dipole magnets in the LHC, LMC , by Gerard Willering 27

When were the magnets powered in SM18? Quench behavior of the main dipole magnets in the LHC, LMC , by Gerard Willering 28

Not all magnets were trained up to A during SM18 reception tests. Firm 3 magnets trained to < A 117 out of 412 (28 %) Part of quenched magnets in that trained to <12750 A. 50 out of 132 (38 %) Quench behavior of the main dipole magnets in the LHC, LMC , by Gerard Willering 29 No direct correlation visible, deeper investigation needed.

Magnet MB 1061 MB 1083 MB 1132 MB 1231 MB 1242 MB 2040 MB 2171 MB 2334 MB 2420 MB 2431 MB 2445 MB 2868 MB 3103 MB 3128 MB magnets were installed in the LHC during LS1 No training quenches were recorded in these magnets during HWC 2015 The number of Firm 3 magnets in this batch is very small. Quench behavior of the main dipole magnets in the LHC, LMC , by Gerard Willering 30

CircuitMagnetCurrent (A)Total time at nominal + delta (hours) Total time at nominal (hours) RB.A RB.A RB.A RB.A RB.A RB.A RB.A RB.A Quenches after completion of training cycle. 31 Quench behavior of the main dipole magnets in the LHC, LMC , by Gerard Willering

32 Linear scale Logarithmic scale For a correct interpretation see: C. Lorin, A. Siemko, E. Todesco, and A. Verweij. "Predicting the quench behavior of the LHC dipoles during commissioning." Applied Superconductivity, IEEE Transactions on 20, no. 3 (2010): cds record Note that the 10 % of magnets that had a thermal cycle were slowest training magnet, with the highest number of quenches. Note that the LHC curve is dominated by a batch of the magnets, while the SM18 data is more homogeneous quench data for all magnets. Different phenomena may apply, slope of the curve may change.