Challenges and Solutions for Reaching Beam Energy Above 3.5 TeV

1. What (else) needs to be done to reach beam energy above 3.5 TeV? N. Catalan Lasheras on behalf of ElQA, MP3 and HWC teams

2. Outline • ElQA non-conformities • RQX.R1 weakness of one quench heater circuit • Insulation weakness of the RB. A78 circuit • Commissioning non-conformities • Long training of correctors • Orbit correctors limitation • Faulty quenches heaters in dipoles • Open and resistive circuits • Other main magnets bus-bar resistance measurements • ElQA qualification voltage shortfalls • Routing of IPQ/IPD bus-bars inside the shuffling module

3. ElQA remaining non conformities

4. MQXA quench heater insulation • One (out of two) QH circuits protecting RQX1.R1 breaks down around 1100V (qualification voltage) • Voltage defined by the energy extraction capacitors (2x450V). • Recommended to recover the redundant QH circuit >3.5 TeV • Solution 1: decrease the charging voltage of the current capacitor to 400V • Less energy delivered to the magnet and less efficient protection • Solution 2: increase the capacitor value and lower the charging voltage • Same total energy and same level of protection. • Feasible operation but for material delivery

5. B30R7 (MB1007) insulation weakness • Magnet breaks down above 1600V. • Nominal qualification voltage 1900 V • 1300 V from quench development inside the coil • 600 V increase of the common mode from dead short in PC. Adjust energy dependent quench voltage to 1000 V → <4 TeV 6771A ~ 4TeV A. Verweij TE-CRG

6. Performance NCs • We seem to be able to live without them, but If required • change QPS protection (underway for RU.R4), development needed for the rest • cooling regulation, consolidation planned for the long shutdown • For the undulator, ramping down the circuits could be necessary at higher energy • Not an issue

7. Training NCs during 2009 • In most cases, training will be needed • The last case, needs to be specifically addressed during this HwC campaign.

8. Training of spool pieces • Training a circuit containing 77 or 154 magnets in series can be long • No an issue • Similar results for RQT/RQTL magnet which presented a long training already during manufacturing tests S. Le Naour TE-MSC

9. Orbit correctors problem • Affects MCBYs and fewer MCBC magnets • Power converter instability • Non nominal transfer function.|| resistance added to the model used by the converter. • Affects other circuits. • The circuit cannot stand the nominal di/dt • We can observe a bump in themeasured current when the magnet quenches • No appreciable degradation in the quenches Y. Thurel TE-EPC

10. Possible short circuit between layers. Will act as a transformer Model simulated in Matlab and Pspice Waiting for test in SM18 of a spare magnet Hypothesis and model Real quench. PM file: 091124-50723.820 M. Dominguez TE-MPE

11. MCBY circuits affected • Last two cases to be confirmed • If required to use higher currents, no solution but to change the SSS

12. Open or resistive circuits ...+ a number of 600A circuits and orbit corrections flagged during the last HwCcampaignfor high splice resistance • Not critical energy defined • Current campaign is going to confirm the number of circuits suspected • Localisation could be carried out by ElQA at cold using local measurements in the tunnel • 2 days per affected sector • Precise within a cell or more • Opening the interconnection and repair

13. Reconfigured protection • Failures in quench heaters found during ElQA or QPS tests • The faulty QH is isolated after integrity test • Reconfigured using spare QH circuits • ROXIE simulations indicate that it should be safe to work at 7TeV • However some cases are potentially dangerous. • QH is open inside the cold mass • QH weak Insulation to ground • It is recommended to change the magnet. (See J-Ph. Tock)

14. “nQPS “of the other main circuits • Recommendation of 2009 review • Measure all bus-bar splices at superconducting state • IPQ, IPD and IT bus-bars protected globally with the magnet • 100mV, 10ms validation time. • nQPS for monitoring resistance under way. • ElQA measurement using local instrumentation and powering cycle • 40 minutes per test 1 to 4 magnets

15. ElQA BB resistance measurements • 36/78 IPQs done during and following technical stops • Results are consistent with block 4 tests and ~1nOhm/splice • A number of tests foreseen during this hardware commissioning campaign ~ 10-12 • Plan to continue during technical stops • System ready for IPDs and IT magnets • Declared ok for below 4TeV • Detect and plan repairs as soon as possible • Reference values for nQPS commissioning • Possible to do IPQs this year but difficult for IPDs and IT R. Mompo TE-MPE

16. Hipot test during the ElQA campaigns • Test have been done according to the procedure EDMS 90327 from 2004 (LHC-PM-ES-0001 rev. 2.0) • Refers to equipment tests from manufacturing to installation in LHC • Operation conditions define the lower voltage the system should withstand • Apply decreasing voltages through manufacturing • Only single circuits vs. ground are considered

17. RQ vs Spools • Spool lines and quadrupole BB run along together inside line M • General protection mechanism will rampdown all of them at the same time • Maximum current is reached almost simultaneously during the pre-cycle.

18. Spool bus-bar routing inside DFBs DFBAs Busbars in lines M1 & M2 All 600 A busbars in the same duct Busbars merged with line N Bundles of n x 4 busbars Correctors Spool A. Perin TE-CRG

19. Voltage withstand test at ElQA • Voltage withstand levels reviewed to take into account cross-talk between circuits in the same line. • The current qualification levels does not cover 3.5 TeV operation for line N correctors

20. Implications • Qualification at higher levels to be planned at cold BEFORE warm-up • HiPot at cold plus diagnostics if needed 2 days per sector ...but, most circuits are used at much less than the pre-cycle values • Alternatives: • Lower the precycle currents (presumably possible for < 7TeV) • Perform precycles at different times and monitor max currents ... Possibly with the exception of a small number of circuits • Possible issue with shorts among bus-bars of the same circuit! • Potential risk for ALL circuits with EE but RB circuits • Already happened in Tevatron on main quadrupoles resulting on a damaged magnet • Avoided in LHC in RCS.A34B2. Localised by ElQA team during the first commissioning. EDMS 885616. No consequences

21. Wrong routing of the BB • Wrong assignment of the three-conductor cable for IPQs inside the shuffling module (EDMS 850864) See KH. Mess in Chamonix 2009 • Couple IPQ circuits during quenches • Affects DFBAO.A,P,H,I, DFBMA in L2 and L8 and DFBLA,B and D. • Heavy operation that should be planned for the long shutdown.

22. Conclusions I • RQX1.R1 QH circuit • Recommended to go back to nominal conditions >3.5TeV • Change of capacitor by QPS plus IST • MB1007 insulation weakness • Need to be changed >4 TeV • Several performance shortfalls • Changes will only be possible during the long shutdown • Orbit correctors limitation • Requires investigation (ElQA, SM18, dedicated MDs) • Changes in the correction could be envisaged >3.5TeV • Repair only possible during the long shutdown • Open and resistive circuits • Requires 2 days of ElQA investigation plus reconnection

23. Conclusions II • Faulty quench heaters in MB magnets • No limitation for energy • A number of magnets to be changed during the long shutdown • Bus-bar measurements on IPQ, IPD and IT • No clear energy limit • Could be done during 2011 TS if given priority • HiPot testing at higher voltage levels • Needed for some(most) LHC circuits > 4TeV (7TeV) • Requires two days per sector before warm-up • DFBs bus-bar routing correction • Not a problem but a nuisance. Could be repaired in the long shutdown