Enhancing Large Hadron Collider Performance for Optimal Operations

1. Abstract- At the end of 2012, the Large Hadron Collider will enter its first programmed long stop (LS1). The problem at the origin of 2008 incident will be definitely treated and the main circuits will then be able to run at the design current value without protection issues. At Chamonix 2011, a proposal was done for a series of powering tests to be performed just before the LS1 to investigate other potential limitations in the machine, which could be fixed during the same maintenance period. A review of these powering tests is presented, together with the list of investigation to be performed by the electrical quality assurance (ElQA) team. A tentative planning is as well proposed. Moreover, following complementary activities during the LS1, a huge campaign of individual system tests will have to be as well performed during the shutdown. Attention will be put on the preliminary list of needed re-qualifications. Mirko Pojer Powering tests before LHC warm-up: What is new from Chamonix 2011? Acknowledgements: R. Schmidt, A. Siemko, G. D’Angelo, S. Fartoukh, E. Metral, M. Giovannozzi, A. Ballarino, R. Denz, K. Dahlerup-Petersen, H. Thiesen

2. Preamble At present, 2 weeks have been allocated for “special” powering tests, to detect possible limitations other than the splices for the design operation of the superconducting circuits (after LS1 there should be no known constrain to the 7 TeV target) Ongoing discussion…

3. Outline • Powering tests to be performed before LS1 • Recap of what presented in Chamonix 2011 • What to push to nominal … and further • Other tests (QPS-”triggered”, etc) • CSCM • CSCM as current bypass quality control: do we want to perform a type test at the end of the year? • Technicalities • ElQA tests • New HV parameters • Special tests • LS1 and after • Individual system test, short-circuit campaign and re-commissioning

4. Status of commissioning in 2008(when we were aiming at the design performance) • Excluding the main circuits (RBs, RQD/Fs) and not considering sector 34, at the end of 2008, all circuits were commissioned to 7 TeV equi. current, except: • RQX.L5 was commissioned to less than 5 TeV, due to change in nominal current • IPDs • I_nom was changed for RD3.R4 and RD4.R4 after commissioning, which then resulted in less than 7 TeV (6.6 and 6.3 TeV, respectively) • RD2.R8 quenched 4 times (5816, 5788, 5856 and 5854 A) at less than 6.8 TeV • 600 A were “jeopardized”, due to the reduction of target current/energy and to the change of specifications • 142 over 410 circuits were commissioned up to 5 TeV or even below • Some 80-120 A were not commissioned for 7 TeV • RCBYV5.L4B2 suffered three quenches without training (limited to 50 A) • RCBYHS4.L5B1 had a hardware problem and was limited to half the energy (limited to 50 A) • RCBYHS5.R8B1 had a ramp-down quench after attaining the nominal (limited to 20 A) • RCBYH4.R8B1 had a ramp-down quench after attaining the nominal (limited to 50 A) • (IPQs all fine for 7 TeV) Commission up to 7 TeV all circuits, in particular: RD3.R4, RD4.R4, RD2.R8 and RQX.L5 plus all missing 600 A circuits plus all circuits in sector 34

5. What to push higher: the Landau octupoles • In Evian ‘11, the request came to commission the Landau octupoles to their nominal current in 2012; in fact, last year they were used in operation at 400 A and more could be needed, if we don’t manage to go to lowchromaticity, to control beam instabilities. • For higher energies: • 550 A could be sufficient at 7 TeV, but tests will be performed in MD this year (E. Metral) • S. Fartoukh estimates that we might need 600A, if not more… • Feasibility and issues to go to 550 A • In 2011 they had been commissioned to 400 A • In 2008, the ROD/Fs were commissioned to 550 A in all sectors but S34, S45 (PNO.b1 missing) and S56 • Among the circuits tested to 550 A in 2008, very few quenches were observed: • ROD.A78B2 had a training quench at 550 A (21/05/08; 17:00) • ROF.A78B2 had a training quench at 460 A (19/05/08; 8:21) • ROF.A81B1 had a training quench at 436 A (20/06/08; 14:00) Commission to 600 A

6. What to push higher: the lattice sextupoles • Concerning the other circuits, S. Fartoukh “would already test the lattice sextupoles up to 600 A, or even discuss/test higher current. Actually this request stands only for the SD circuits in s81,12,45,56 (so 16 out of 64 circuits).” • In 2008, they were commissioned to 550 A in S45 and in S81; elsewhere, they were commissioned to 400 A. • Is the acceleration an issue? • "Biensurla longeur des segments risque de devenir de plus en plus grand a petit beta* (ne serait-ce que pour le controle des RQ6 en IR1 et IR5 qui finissent a 210 A pour beta*=60 cm!), mais ceci te montre qu'un gain d'un facteur 2 dans d2I/dt2 des RSs serait bienvenu deja cette annee, et sera sans doute indispensable a 6.5 TeV et beta*=45 cm. Puis si ATS en plus a 40cm et 6.5TeV, alors disons 1A/s2 serait formidable, sinon un squeeze infiniment long ou pendant lequel on ne peux plus redemarrer si on s'arrete a un certain beta* "(S. Fartoukh) Commission to 600 A – improve acceleration reducing I_nom in 2012? QPS issue: with the present acceleration, we are at the limit of the detection threshold After LS1, a new generation of detectors will be available, which are less sensitive to inductance

7. Can we test the MO or MS to more than 600 A? • From the magnets point of view, could be feasible (at least for the MO) • But there are some technical limitations to consider: • The power converters are limited to 600 A (RPMBB Designation PC:[600A 10V 4Q] CRWB:600A DCCT:600A Mode:DCType:B without DC contactor) • Not easy, from regulation point of view, to put two in parallel • The current leads are dimensioned for 600 A max and have been validated for this value. Larger current values would require further testing at a different temperature regulation (overcooling) • For the QPS “in principal there are no constraints up to 600 A. The QPS current sensors are limited in range to ±600 A and there is a programmed interlock at ±610 A, meaning that you cannot exceed this current.” [R. Denz] Courtesy of A. Ballarino

8. Surprises might appear while commissioning to nominal • Re-training in 2010(2-quenches rule introduced to shorten commissioning) • RCD.A45B1 - NC 1035252 - quenched twice (at 300 and 391 A); limited to 400 A • RCD.A56B2 - NC 1026728 - quenched twice (at 479 and 496 A); limited to 450 A • RCD.A81B1 - NC 1043522 - quenched twice (at 351 and 484 A); limited to 450 A • RQTL11.L2B2 - NC 1020622 - quenched (544.85 A); limited to 500 A • RQTL11.R5B1 - NC 1027448- quenched twice (at 501 and 492 A); limited to 450 A • RQTL11.R5B2 - NC 1027413 - quenched twice (at 550 and 533 A); limited to 450 A • RQTL11.L6B1 - NC 1026809 - long training (353, 292, 340, 350, 384 A); limited to 300 A • RQTL11.L6B2 - NC 1026747 - long training (267, 348, 384, 354, 382 A); limited to 300 A • RQTL8.L7B1 - NC 1046464 - quenched twice (at 240 and 257 A); limited to 200 A • RQTL9.R3B2 - NC 1046992 - quenched at 359, 399.9 and 396.1 A; limited to 400 A • RQT13.L5B1 - NC 1060679 - this magnet shows a strange behavior; I_PNO reduced to 400 A • RCBCV5.R5B2 - NC 1029792 - quenched twice (at 69.4 and 76.9 A); limited to 72A • RCBCH7.R3B1 - NC 1046994 - quenched twice (at 98 and 95 A); limited to 80 A • RCBYH4.R8B1 - NC 1051795 - quenched at 55.6 A; limited to 50 A • RCBYV5.L4B2 - NC 1049055 – 3 quenches w.o. training (63.3, 65.7 and 64.7 A); limited to 50 A • RCSSX3.L1 - NC 1053719 - the circuit trips when it reaches 62.9 A; this has been proven 4 times (circuit is now locked) • RCBYHS5.R8B1 - NC 1063839 - circuit quenches when coming down from +-nominal current to zero; the control of the current also shows high instability (see EDMS 1053978) • RCBYHS4.L5B1 - NC 1053709 - circuit can not handle di/dt : weak magnet known since 2008 (see MP3 meeting 4/11); tested with reduced I_PNO up to 60 A and OK so new I_PNO defined at 50 A Used in 2012 operation 125 113 151 139 114 127 132 152 169 27 -124 -163 18 -34 43 -48 -79 5 -193 -113 -56 46 17 -128 -89 -23 -117 -15 -6 186 134 39 600 A 80-120 A Not powered to 7 TeV in 2008

9. What to do in case of training? • How many quenches should we accept on the RD circuits? • 4 or 5 quenches should be the minimum… • Can we accept more? • How many quenches should we accept on the 600A and 120A circuits? • Should we go up to 10 quenches? • Should we stop earlier: • accept a limitation in the machine? • check for a different optics? • Review operational currents according to real operation needs All this will have to be addressed during the year together with the nMP3 colleagues and a proposal should be made to LMC Review and update with 2011-12 experience!!! Detailed procedures shall be prepared before the start of the powering tests

10. Strategy for the powering tests • Full support by experts (QPS, EPC) during the testing phase • nMP3 should quickly analyze critical cases • To reduce the impact on other activities (see later, ElQA), powering tests will have to be performed during evening/night for the high current circuits; 600 A and below are in phase I • Documentation: • Powering procedures will be written this year on the tests to perform and the way to execute them • Status report will be written after the campaign, including • Powering history • Electrical NC • ElQA test results: transfer function, etc…

11. What else do we need to test? • QPS • Test of the RQTD/Fs with different logic for the tune FB (test of new boards) • Test of the RCBXH3.L5 • Not clear where the fault is • This circuit will be certainly needed at high energy • Test of the undulator? (a series of tests is foreseen for the spare in SM18) • Do we want to fire all quench heaters to full voltage to check if there are critical cases in the machine? (a monitoring tool will be in place only during TS1, that compares the discharge with a reference [K. Dahlerup-Petersen])

12. Powering tests to be performed before LS1 • Recap of what presented in Chamonix 2011 • What to push to nominal … and further • Other tests (QPS-”triggered”, etc) • CSCM • CSCM as current bypass quality control: do we want to perform a type test at the end of the year? • Technicalities • ElQA tests • New HV parameters • Special tests • LS1 and after • Individual system test, short-circuit campaign and re-commissioning

13. Risks associated with a quench • In normal conditions, the current is circulating through the splice, into the magnet and back from the busbar through the other splice • When a quench occurs, the voltage drop inside the magnet is increasing, the diode starts conducting and the current starts flowing inside the bypass line • The diode is resistive and starts to heat up • The heat could propagate through the cable up to the splice and eventually quench it--> serious damages if not conform! • Quench tests were performed to address this issue (proposal Chamonix 2011, F. Bordry) • Collateral discovery: the resistance during discharge via the bypass is much higher than expected In the machine we have 2000 of these bypasses that have never been tested More details in Andrzej’s presentation in Session 4 A16R5 anode: 2 consecutive quenches at 5 kA

14. Copper Stabilizer Continuity Measurement (thermal amplifier) • Technique proposed by H. Pfeffer and later developed by H. Thiesen et al. to investigate thermal runaway of faulty splices of an entire line • The method could be used to test all bypass current in the same line Magnets at 20 K Ramp to 500A with 20V/s to open all diodes Check if diodes are open Ramp up to plateau current with 300A/s Plateau current (up to a maximum of 60s) Discharge if U>Uthreshold Ramp down to 0 A with 300A/s if U<Uthreshold All technical problems addressed. No showstopper identified. Another review in foreseen after summer

15. CSCM: type test time allocation

16. Powering tests to be performed before LS1 • Recap of what presented in Chamonix 2011 • What to push to nominal … and further • Other tests (QPS-”triggered”, etc) • CSCM • CSCM as current bypass quality control: do we want to perform a type test at the end of the year? • Technicalities • ElQA tests • New HV parameters • Special tests • LS1 and after • Individual system test, short-circuit campaign and re-commissioning

17. ElQA • 2.2 HVQ - HIGH VOLTAGE QUALIFICATION • Each circuit is energized individually with respect to ground using a DC voltage source limited to a current of 2 mA and applying a test voltage as defined in the annex B. During the test of a given circuit, all other circuits of the same electrical safety subsector are grounded for safety reason. • Dipole lines (go and return) are tested separately, since the circuit can be interrupted at the level the warm cable connection • Tests of the two bus-bars of RQ together, the bus cannot be interrupted • In the future, maximum operational voltage against any neighbouring circuit will be taken into account • Which electrical circuits have bus-bars running in the vicinity? • Consider nested circuits • Maximum operation voltage x1.2 Reference documentation

18. ElQA

19. ElQA • Another important activity of the ElQA team will consist in filling a reference map to be used during and after LS1: • MIC – measurement of the quench heater resistance quench heater insulation (vs coil and ground) • TFM – to be performed at cold and repeated at warm • Also a series of investigations will be performed on ill circuits, mainly to diagnose shorts (RCOs, 120 A circuits,…) • Internal Splice Resistance Measurements will be performed in Feb-Mar (and later during the technical stops) on the Inner Triplets; if not completed, they will be carried out at the end of the year as part of the powering tests • We could re-measure the resistance of internal splices for critical magnets, to confirm the need for replacement (might be possible during technical stops)

20. Conclusions • Powering tests • Commission to nominal current all circuits (RB and RQD/F excluded) • Commission to ultimate the ROD/Fs and the RSD/Fs • What about higher currents for the circuits above ? If needed, some measures must be already taken – feasibility study • CSCM • Time and resources for a type test have been considered • Could we envisage to test more than a sector? • ElQA • Qualification of all superconducting circuits to revised voltage levels • Reference map before LS1 • Special investigations A lot of material for discussion with nMP3 and LMC • Time estimate • 3-4 days per sector for the powering tests (could do more sectors in parallel) • 3 days with 2 teams per sector for the MIC • 2days with 2 teams per sector for the HVQ • ‘few’ additional days for special investigations by ElQA Tight to complete in the allocated time!!!

21. Powering tests to be performed before LS1 • Recap of what presented in Chamonix 2011 • What to push to nominal … and further • Other tests (QPS-”triggered”, etc) • CSCM • CSCM as current bypass quality control: do we want to perform a type test at the end of the year? • Technicalities • ElQA tests • New HV parameters • Special tests • LS1 and after • Individual system test, short-circuit campaign and re-commissioning

22. The LS1 will be the occasion for more than splice consolidation • Many system upgrade and maintenance activities will be performed during the LS1 • QPS upgrades: • additional systems for the diagnostics of the quench heater circuits (measure of the resistance of the heater circuit with high precision - ΔR = 100 µΩ- in order to see precursors of eventual faults [R. Denz] • Specific transducers for precision measurement of the power pulse during heater discharge of each of the 6076 heater circuits in the LHC [K. Dahlerup- Petersen] • All other QPS instrumentation cables need to be checked after LS1 for electrical insulation strength and correct wiring • Detectors change and firmware upgrade • Power converter modifications (active filters, auxiliary power supplies,…) • Following R2E relocations, many electronic equipment will be removed from areas close to the tunnel and put far away (see A.L. Perrot in this same session) • Cable re-routing (mainly at point 5, due to R2E) and change of cable sheaths

23. The impact on re-commissioning • All the above interventions will demand (before commissioning with powering test) for a massive campaign of individual system tests, to check for • systems reliability • protection functionalities • effective QPS-PIC-PC interface • The cable activity will in particular require for short-circuit tests and heat runs to be performed • New powering procedures will be needed (not only for the training of the 13 kA circuits) • And later, we will have a brand new commissioning More than 6 months of powering tests where the manpower could become an issue (OP will be involved in splice consolidation). Should we resume the figure of the Point Owners?

24. Point Owner Thanks for your attention!