1. Running in 2012 @ 4 TeV/beam Preamble Is it worth from the Physics point of view? What do we gain in terms of luminosity? What is the overhead in terms of machine/beam commissioning? 14/12/2011 R. Alemany, Evian 2011, Session 8: 2012 1/18 Many thanks to: L. Bottura, E. Todesco, J. Wenninger, M. Zerlauth, E. Nebot, 2xB. Holzer, J. Steckert, A. Siemko, M. Brugger, M. Lamont, P. Baudrenghien, E. Shaposhnikova, T. Baer, L. Pape, P. Sphicas, J. Varela, V. Kain, R. Assmann, R. Schmidt, M. Koratzinos

2. Preamble Why LHC did not run @ 4 TeV in 2011?  Let’s recall Chamonix 2011: 14/12/2011 R. Alemany, Evian 2011, Session 8: 2012 2/18 Main argument against running @ 4 TeVStatus at the end of 2011 (Un)known number of expected quenches in 2011 (20 in 2010) HW = 0 quenches Beam = 1 single-magnet spurious quench with beam* Ref: A. Verweij, Probability of burn-through of defective 13 kA joints at increased energy levels, Chamonix 2011 * Firing of Quench heater probably due to SEU, but not proven There is the (≈)same risk associated with running at 4 TeV and 3.5 TeV  down time of 8-12 months given the present consolidation status QPS consolidation work all over the year Snubber capacitors installed in all dipole circuits Efficient BLM protection

3. Is it worth from the Physics point of view? 14/12/2011 R. Alemany, Evian 2011, Session 8: 2012 3/18 Ref: P. Sphicas, View on CMS and ATLAS results, APPS 2011, Nov 30 – Dec 02, 2011 gg  H (H  ϒϒ,ZZ,WW) Factor ~ 1.2 qq, gg Factor ~ 1.5 qq, gg, qg Factor ~ 4 Mx (GeV) qq Factor ~ 3.5

4. What do we gain in terms of luminosity? 14/12/2011 R. Alemany, Evian 2011, Session 8: 2012 4/18 F: Xangle factor =f(ϵ,β*)!! 1. Due to ϵ↓:2. Because ϵ↓  more aperture margin at the IT & TCT  we get↓β*: ~14% L ↑ for free from ε shrink due to 12.5% E ↑ 30% L ↑ from ε & β* shrink +23% L ↑ if β*=0.7m L (cm-2s-1) F ϵnϵn Pile-up ϵnϵn 30 35 40 25 20 15 10 N b =1380 N 1 =N 2 =1.5 10 11 p+/bunch

5. Overhead in terms of HW Commissioning Main circuits Extra powering tests  today the powering test stops @6000 A; two extra steps @7000 A would be needed: One cycle One energy extraction from QPS Time estimate: ~ 5 hours/circuit (circuit = RB, RQD, RQF) Inductance coefficients recalculation (at least 2 ramps one per QPS board) RB.A78 - ElQA tested up to 1.6 kV instead of 1.9 kV due to bad insulation on magnet B30.R7 (NC 1060444) --> limited to 4 TeV, veto to be lifted for higher energies Things that are not needed Reconfiguration of energy extraction – not for 4 TeV (certainly needed for 5 TeV)  See next slide Change of nQPS thresholds to adapt to reduced quench margin (not for 4 TeV) No quench issue expected till ~5 TeV (RB.A78 had a training quench below!) 14/12/2011 R. Alemany, Evian 2011, Session 8: 2012 5/18

6. Energy Extraction System 14/12/2011 R. Alemany, Evian 2011, Session 8: 2012 6/18 ** nQPS SymQ Thresholds will have to be recalculated for 6800 A ? OK to go Ref: J. Steckert, Implication of increased beam energy on QPS, EE, Time Constants, Chamonix 2011 τ (time constant) Limit= 150 Limit= |15.5| **

7. Overhead in terms of HW Commissioning Inner Triplets: All commissioned up to 5 TeV except: IT.R1  weak electrical insulation of QH YT1121 to coil and/or ground (NC 1017174) --> limited to 3.5 TeV without QH reconfiguration (high capacitance PS) Dedicate Quench Heater Power Supply under construction to be installed and ready for start up with beam 14/12/2011 R. Alemany, Evian 2011, Session 8: 2012 7/18

8. Overhead in terms of HW Commissioning IPQ/IPD The current powering test commissions them up to 3.5 TeV. What has to be done is, simply, to extend the last powering test to I_PNO corresponding to 4 TeV. Others 600 A  5 TeV 120 A  5 TeV 60 A  7 TeV Total Estimated Overhead  3 days 14/12/2011 R. Alemany, Evian 2011, Session 8: 2012 8/18

9. UFOs: Energy Extrapolation 14/12/2011 R. Alemany, Evian 2011, Session 8: 2012 9/18  17 dumps by UFOs in 2011:  11  MKI UFOs  4  UFOs @Experiments  2  Arc UFOs Ref: T. Baer, UFOs at LHC, Evian Workshop 2011 3 dumps at 4 TeV by Arc UFOs Losses of all arc UFOs in 2011 are scaled up = f(energy  Eduardo’s IPAC’11 paper) and compare to the BLM thresholds at the corresponding energy (MKI UFOs scale similarly with energy) Signal/threshold for UFOs is about 55% higher at 4TeV than at 3.5 TeV. Hence, we would have had 3 dumps if we were running at 4TeV this year, compared to 2 dumps which we actually had. For >1000 bunches the UFO rate ~ kte  energy dependence takes over > 5 TeV Not included (margin between BLM thresholds and actual quench limit, 25ns bunch spacing, intensity increase, beam size, scrubbing) Data 14.04. and 31.10.2011

10. SEU Evolution 2011 14/12/2011 R. Alemany, Evian 2011, Session 8: 2012 10/18 Ref: G. Spiezia, M. Brugger, M. Calviani, J. Mekki for R2E, Overview of R2E related events during 2011, CERN-R2E Review 12.11.11 Ref: G. Spiezia, R2E – experience and outlook for 2012, Evian 2011 50% of the events are located in the Dispersion Suppression elements and are dominated by QPS The most critical areas are UJ14/UJ16 where 50% of the events provoked a beam dump By Equipment QPS SEU: Reiner’s talk on Monday  mitigation measures during Xmass’11 shut down to keep the SEU kte regardless the luminosity Cryo SEU: Serge’s talk on Monday  mitigation measures during Xmass’11 22% of STABLE BEAMS fills were dumped by SEU  Markus’ talk on Monday 480b 768b 912b 1092b 1236b 1380b

11. SEU: Summary & Forecast 14/12/2011 R. Alemany, Evian 2011, Session 8: 2012 11/18 Ref: G. Spiezia, M. Brugger, M. Calviani, J. Mekki for R2E, Overview of R2E related events during 2011, CERN-R2E Review 12.11.11 LHC Ref: J. Christiansen, SEE’s In the LHC experiments, CERN-R2E Review 12.11.11 EXPERIMENTS 2012 prediction No mitigation  With mitigation 150 SEU  45 SEU Ref: G. Spiezia, R2E – experience and outlook for 2012, Evian 2011

12. BLM 14/12/2011 R. Alemany, Evian 2011, Session 8: 2012 12/18 X axis = dump threshold for 40 μs RS Y axis = maximum noise observed in each monitor during a period of NO BEAM Ideally everything should stay below 10%  we have some margin and we are confident that we would not dump on noise spikes. A few monitor go above 10% of the threshold and it will be studied whether or not need new thresholds. Data from 34 hours starting on 2011-11-07 07:00:00 (last technical stop) NOISE at 100% of dump thresh. NOISE at 10% of dump thresh. 450 GeV 3.5 TeV 4 TeV Dump Threshold 40 μs RS (Gy/s) (from simulations) Noise (Gy/s) E. Nebot

13. LBDS XPOC BLM limits  extrapolated to 4.0 TeV from 2011 measurements at energies up to 3.5 TeV (Likely) to be fine tuned during operation when data with high intensity dumps at 4.0 TeV are available. Abort gap cleaning  validation at 4.0 TeV needed but probably this will be requested any way if 3.5 TeV after the winter TS The energy of the LBDS is presently clamped at 5.0 TeV (in the Beam Energy Interlock)  no changes to be made at 4.0 TeV TCDQ  functions to be extended to 4.0 TeV (like all the other collimators) 14/12/2011 R. Alemany, Evian 2011, Session 8: 2012 13/18 BTVDD B1 1380 bunches @ 3.5 TeV

14. Machine Protection Validation Standard MP tests to be done irrespective of the energy The exact details also depend on changes that are made in the stop (that may be unrelated to the energy itself !). Tests at 4 TeV take a bit longer since the ramp will be longer (84 s!) Settings @4 TeV will be different (BLMs, etc)  to be checked more carefully (since the values change), but most of this will be transparent 14/12/2011 R. Alemany, Evian 2011, Session 8: 2012 14/18

15. RF: Longitudinal stability 15/18  Broadband stability criteria  Narrow-band stability criteria  Without blow-up the threshold quickly decreases during the acceleration ramp  With a blow-up that keeps bunch length constant, the threshold increases linearly with the RF voltage  Thanks to the longitudinal blow-up, the stability is actually improved during the acceleration ramp as the voltage rises  At constant bunch length and voltage, it is independent of energy Ref: E. Shaposhnikova, Longitudinal Beam Parameters during acceleration in the LHC, LHC Project Note 242, Dec 2000 14/12/2011 R. Alemany, Evian 2011, Session 8: 2012 Courtesy of P. Baudrenghien & E. Shaposhnikova

16. Chromaticity Control @ 4 TeV 14/12/2011 16/18 Ref: N. Aquilina, E. Todesco, Decay of chromaticity at injection and operation at 4 TeV, LMC 07.12.2011 R. Alemany, Evian 2011, Session 8: 2012 N. Mounet, Impedance effects on beam stability, Evian S7  We learnt the importance of keeping the chromaticity under control next year if tight collimator settings.

17. Re-commissioning in 2012 14/12/2011 R. Alemany, Evian 2011, Session 8: 2012 17/18 Ref: M. Lamont, Operational Overhead of Moving to Higher Energies, Chamonix 2011 2012 2

18. Conclusion No show-stoppers from equipment point of view Total commissioning overhead  half a week ~ Same Probability of burn-through of defective 13 kA joints as for 3.5 TeV Risk @ 3.5 TeV ≈ Risk @ 4 TeV  down-time 8-12 months Important Gain in cross-section & luminosity ( L  ~ 30%)  Running @ 4 TeV in 2012 is WORTH DOING! 14/12/2011 R. Alemany, Evian 2011, Session 8: 2012 18/18

19. Dipole B30R7 14/12/2011 R. Alemany, Evian 2011, Session 8: 2012 19 QUALIFICATION VOLTAGE 1600 V = 600 V (EE+PC) + 1000 V (Voltage inside the coil) Simulated MIITS by A. Verweij Main arc dipole Voltage developed in the coil 1000 V 6771 A ~ 4 TeV Only a change in the energy extraction resistors = decay time constant during a FPA, could release the veto on the 4 TeV, however at Chamonix 2011 this solution was not considered safe RB.A78 - ElQA tested up to 1.6 kV instead of 1.9 kV due to bad insulation on magnet B30.R7 (NC 1060444). Fault inside the cold mass, no possible to repair in situ  the Emax for which the use of this magnet is still safe is 4 TeV, above this energy the magnet should be replaced.

20. Preamble What has radically reduced the number of spurious quenches in 2011: QPS consolidation work all over the year Snubber capacitors installed in all dipole circuits Efficient BLM protection 14/12/2011 R. Alemany, Evian 2011, Session 8: 2012 20 Ref: F. Bordry, LHC Energy in 2012 3.5 TeV or 4 TeV, LMC 30 th Nov 2011

21. Preamble Possibility asynchronous dump with multiple quenches (S56&S67)  Possibility of bus bar quenches + blindness of the nQPS SymQ if > 15 magnets quench 1 in 2010***, 0 in 2011 (N.B. S56-65 good sectors in terms of Rspl,max) 14/12/2011R. Alemany, Evian 2011, Session 8: 2012 21 Limit= 150 Limit= |15.5| ** ** nQPS SymQ Thresholds will have to be recalculated for 6800 A OK to go Ref: J. Steckert, Implication of increased beam energy on QPS, EE, Time Constants, Chamonix 2011 ***2010: faulty power MOSFET in one of the trigger fan-out units qith ion pilot beam; no losses. τ (time constant)

22. FLUKA Studies of the asynchronous beam dump effects on LHC point 6 14/12/2011 R. Alemany, Evian 2011, Session 8: 2012 22 quenches have to be expected quenches are possible quenches are unlikely to happen 1 2 3 4 5 MQY.4R6 1, MQY.5R6 2, MB.A8R6 3, MB.B8R6 4, MQML.8R6 5 5 magnets will quench for sure + 3 possible = 8 magnets Energy deposition in bus bars ~ tenth mJ cm-3; but for bus bars in cell C8.R6 peaks a factor 10 higher are expected Systematic uncertainties = factor 5 to 10! Ref: R. Versaci et al, FLUKA Studies of the Asynchronous Beam Dump Effects on LHC Point 6, CERN-ATS-2011-236 Eb = 4.5 TeV  150 MJ 50 ns bunch spacing, 42 bunches are swept from ideal trajectory = ~5 10 12 p+

23. Preamble On top of this: the analysis of pyramid tests and ~375 ramps to 3.5 TeV allowed to consolidate the Maximum Splice Resistance (R spl,max ) knowledge in a Bus Segment over LHC and so far, no degradation with time has been observed 14/12/2011 R. Alemany, Evian 2011, Session 8: 2012 23 Splice TypeMagnetRspl,max (nΩ) Comments Bus segmentRB,RQD/F0.3±0.8Few ~ 3 nΩ Intramagnet * RB3.3±0.98 dipoles Intramagnet * QRD/F1.2±0.83+2 quad * Intramagnet splices are less dangerous than bus segment splices, since the former are protected by the diodes. Additionally, all intramagnet splices have already been exposed to quenches. Ref: Z. Charifoulline, Current Status & Long Time Evolution of Main Splice Resistances at 1.9K, 2nd LHC Splice Review, 29.11.2011 However, the knowledge of the copper stabilizers status in the machine has not changed

24. Preamble 14/12/2011 R. Alemany, Evian 2011, Session 8: 2012 24 The error bars are the RMS spreads of the distributions Mean RRR of the copper busbar of the machine: 250±50 All sectors measured Ref: F. Bordry, LHC Energy in 2012 3.5 TeV or 4 TeV, LMC 30 th Nov 2011