Running in 2012 @ 4 TeV /beam

1. Running in 2012 @ 4 TeV/beam R. Alemany, Evian 2011, Session 8: 2012 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? 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: • QPS consolidation work all over the year • Snubber capacitors installed in all dipole circuits • Efficient BLM protection 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 R. Alemany, Evian 2011, Session 8: 2012 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

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

4. What do we gain in terms of luminosity? 1. Due to ϵ↓: 2. Because ϵ↓ more aperture margin at the IT & TCT  we get↓β*: F: Xangle factor =f(ϵ,β*)!! 30 35 40 10 20 15 25 Nb=1380 N1=N2=1.5 1011 p+/bunch ~14% L↑for freefrom ε shrinkdue to 12.5% E ↑ R. Alemany, Evian 2011, Session 8: 2012 L (cm-2s-1) Pile-up F 30% L↑ from ε& β* shrink +23% L↑ if β*=0.7m ϵn ϵn

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!) R. Alemany, Evian 2011, Session 8: 2012

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

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 R. Alemany, Evian 2011, Session 8: 2012

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 R. Alemany, Evian 2011, Session 8: 2012

9. UFOs: Energy Extrapolation • 17 dumps by UFOs in 2011: • 11  MKI UFOs • 4 UFOs @Experiments • 2 Arc UFOs 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) Data 14.04. and 31.10.2011 R. Alemany, Evian 2011, Session 8: 2012 3 dumps at 4 TeV • 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 (marginbetween BLM thresholdsandactualquenchlimit,25ns bunchspacing,intensityincrease, beam size, scrubbing) Ref: T. Baer, UFOs at LHC, Evian Workshop 2011

10. SEU Evolution 2011 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 R. Alemany, Evian 2011, Session 8: 2012 • 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 1380b 1236b 1092b 912b 768b 480b 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

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

12. BLM X axis = dump threshold for 40 μs RS Y axis= maximum noise observed in each monitor during a period of NO BEAM • 450 GeV • 3.5 TeV • 4 TeV Noise (Gy/s) NOISE at 100% of dump thresh. NOISE at 10% of dump thresh. E. Nebot R. Alemany, Evian 2011, Session 8: 2012 Dump Threshold 40 μs RS (Gy/s) (from simulations) • 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)

13. LBDS BTVDD B1 1380 bunches @ 3.5 TeV • 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) R. Alemany, Evian 2011, Session 8: 2012

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 TeVwill be different (BLMs, etc)  to be checked more carefully (since the values change), but most of this will be transparent R. Alemany, Evian 2011, Session 8: 2012

15. RF: Longitudinal stability • 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 R. Alemany, Evian 2011, Session 8: 2012 Courtesy of P. Baudrenghien & E. Shaposhnikova • Ref: E. Shaposhnikova, Longitudinal Beam Parameters during acceleration in the LHC, LHC Project Note 242, Dec 2000

16. Chromaticity Control @ 4 TeV 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. R. Alemany, Evian 2011, Session 8: 2012 Ref: N. Aquilina, E. Todesco, Decay of chromaticity at injection and operation at 4 TeV, LMC 07.12.2011

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

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! R. Alemany, Evian 2011, Session 8: 2012

19. Dipole B30R7 • 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. QUALIFICATION VOLTAGE 1600 V = 600 V (EE+PC) + 1000 V (Voltage inside the coil) Main arc dipole R. Alemany, Evian 2011, Session 8: 2012 1000 V Voltage developed in the coil 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 6771 A ~ 4 TeV Simulated MIITS by A. Verweij

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 R. Alemany, Evian 2011, Session 8: 2012 Ref: F. Bordry, LHC Energy in 2012 3.5 TeV or 4 TeV, LMC 30th Nov 2011

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

22. FLUKA Studies of the asynchronous beam dump effects on LHC point 6 Eb = 4.5 TeV 150 MJ 50 ns bunch spacing, 42 bunches are swept from ideal trajectory = ~5 1012 p+ MQY.4R61, MQY.5R62, MB.A8R63, MB.B8R64, MQML.8R65 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 1 2 quenches have to be expected 3 quenches are possible 4 5 R. Alemany, Evian 2011, Session 8: 2012 quenches are unlikely to happen 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

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 (Rspl,max) knowledge in a Bus Segment over LHC and so far, no degradation with time has been observed However, the knowledge of the copper stabilizers status in the machine has not changed * 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. R. Alemany, Evian 2011, Session 8: 2012 Ref: Z. Charifoulline, Current Status & Long Time Evolution of Main Splice Resistances at 1.9K, 2nd LHC Splice Review, 29.11.2011

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