Bailey, R

Redaelli, S

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THE MINIMUM WORKABLE LHC: PLANS AND REQUIREMENTS FORBEAM COMMISSIONING, YEARS 1 AND 2 - DISCUSSIONChairman: R. Bailey - Scientific secretary: S. RedaelliCERN, Geneva, SwitzerlandSUMMARY OF OVERALLCOMMISSIONING STRATEGY FORPROTONS (R. BAILEY)M. Huhtinen asks when the change from 75 ns spacingto 25 ns will take place. R. Bailey replies that this basicallydepends on the requests from the experiments and on howthe overall commissioning will proceed. It is not possibleto predict now the required time for the transition.S. Myers asks whether or not the operation at 75ns is re-ally necessary. Why can’t we go directly to the nominal25ns operation? R. Schmidt agrees that in principle, formachine protection issues, what matters is the total beamintensity and this could be achieved at 25ns spacing withless intensity per bunch. B. Bailey says that the 75ns op-eration would be useful to relax the operation procedurein various respects, without requiring major modificationswith respect to the nominal cycle. In this respect, R. Ass-mann stresses that a clear advantage is that the beam-beameffects, which are expected to seriously affect the LHC per-formance, will be greatly reduced with larger bunch spac-ing. M. Huhtinen comments that for the detector triggerit could be useful to operate for some time with a reducedbunch repetition frequency.M. Huhtinen also asks what is the effect of the operationwith shifted IP at LHCb on the other detectors. R. Baileyreplies that this will induce, likewise, IP shifts at the otherIP’s.R. Assmann comments that the TOTEM operation withlarge    at IP1 and IP5 might be of a concern for the beamcleaning. Ralph asks if there are detailed plans on when theTOTEM operation will take place. K. Eggert replies that heis trying to fit the TOTEM operation into the 43-on-43 op-eration, with minimal impact on the schedule. This wouldminimize the impact on the commissioning schedule. Apossible solution could be to have some runs with interme-diate    once the 43-on-43 operation will be established.For example, an optics with      m is presently underinvestigation.S. Myers stresses strongly that as soon as possible itshould be worked out in detail when to switch to the ionand TOTEM operations. It is clear that these are majorvariations of the operation routine that could significantlyslow down the path towards the commissioning of protonruns, which for the time being is the highest priority forthe early LHC operation. The experiments must urgentlyexpress their priorities.ELECTRICAL CIRCUITS REQUIREDDURING COMMISSIONING(M. GIOVANNOZZI)R. Saban welcomes the list of the circuits that couldin principle be commissioned after the LHC startup withbeam. However, he underlines that it is clear that any com-missioning of subsystems performed with closed machinewill be very critical. The baseline is to test everything atonce before starting the beam runs.S. Myers asks what is the point of talking about correc-tion of high-order effects (Q”, Q”’, ...) if at startup onemight not be able to even measure the quantities to correct.M. Giovannozzi replies that, since the multipole errors ofthe various magnet types will be measured, one should ad-just the corrector values fields to compensate the knownfield errors. Steve agrees.R. Assmann asks if the (possibly) delayed correctors willbe properly installed (cabling, power supplies, ...). Mas-simo replies that this will certainly be the case. All the cor-rectors will be available. In case of problems/delays duringcommissioning, the commissioning of some correctly fam-ilies could be delayed without affecting the stage I opera-tion of the LHC.However, R. Wolf stresses that for superconducting cor-rectors it is not easily possible to switch off the magneticfield. As soon as they are powered once, they require fullcommissioning otherwise their magnetic history will not beknown and one will not be able to know their operationalconditions. Only if the corrector circuits are NEVER pow-ered one can ensure that they will produce no field.K.H. Mess comments that the gain of not commissioningthe few circuits that are not strictly required at day-1 seemsextremely marginal because only a few families would beexcluded. Better to do everything properly!BEAM MEASUREMENTS REQUIRED INTHE FIRST TWO YEARS OF LHCCOMMISSIONING (F. ZIMMERMANN)P. Limon asks if there are plans to systematically test thevarious measurement equipments. For example, what is thestrategy to make sure that the BPM’s will be operational?F. Zimmermann replies that we will try to test as many de-vices as possible at the sector test this year. Concerningthe BPM’s, R. Steinhagen states that the LHC system is in-trinsically redundant and there is no doubt that we will beable to make use of it. Nevertheless, there are diffused con-cerns that a systematic plan should be carried out to makeLHC Project Workshop - 'Chamonix XV'80sure that the various measurement equipment are properlychecked out.R. Schmidt comments that various measurements amongthe list proposed by F. Zimmermann depend on beam en-ergy and intensity. It should be defined which measure-ments can be done at which beam energy. Measurementsthat can potentially put in danger the machine should beclearly identified. F. Zimmermann replies that most of themeasurements he proposed can be carried out with pilotbeam and should therefore not put in danger the machine.J.P. Koutchouk states that for the LHC it will be an issueto figure out which BPM’s give a wrong signal. He sug-gests that, at the latest at the next Chamonix workshop, sys-tematic methods to assess the BPM measurements shouldbe figured out.REAL-TIME FEEDBACK REQUIRED(R. STEINHAGEN)R. Assmann asks if there are systematic effects that areexpected to limit the performance of the orbit feedback sys-tem. For example, it is known that setting up an orbit feed-back at LEP took a long time. R. Steinhagen believes thatcritical issues for the LHC might be coupling and chro-maticity. J. Wenninger comments that the setup of an orbitfeedback at LEP was slowed down by lack of manpowerand lack will rather than by fundamental problems. S. My-ers agrees.Q. King asks if we will have real-time input into theRF’s. R. Steinhagen replies that technically this is possible(compatible with the available hardware) but this solutionshould be approved bu the RF experts.VACUUM CONDITIONS REQUIRED(V. BAGLIN)The proposal by V. Baglin of starting up the LHC withreduced vacuum performance in the long straight sections(LSS) triggers various comments: There is a general con-cern (ATLAS, CMS) that the luminosity performance ofthe LHC with reduced vacuum in the LSS’s might con-siderably affect the detector commissioning in early LHCoperation. So far, the detector commissioning plan has as-sumed that the nominal vacuum will be available from day1. Therefore, a start-up with reduced vacuum performanceshould be approved by the experiments before a decision ismade.K. Potter stresses that ALICE and LHCb might be partic-ularly affected by vacuum problems (signal-to-noise ratiowill worsen more than at CMS and ATLAS).J. Jowett comments that the statement that “worse vac-uum performance is acceptable for IBS emittance growths”does actually not take into account the operation with leadions. This issue should be addressed.T. Linnecar expresses some concerns for the operationof the RF’s with poor vacuum. This issue has not beenconsidered by V. Baglin but deserves more detailed studies.R. Assmann says that the proposed solution with reducedvacuum performance is also supported by the collimationproject. The installation of collimators at IR3 and IR7 willbe facilitated by a staged installation at the cleaning inser-tions (collimators produced later could be installed at anymoment if the insertions will not be baked out).RADIATION PROTECTIONCONSTRAINTS DURING THE LIFE TIMEOF LHC (M. BRUGGER)No discussion after the talk.BEAM COMMISSIONING: REQUIREDAPPLICATIONS (M. LAMONT)S. Myers asks whether there will be applications to checkthe magnet polarities. M. Lamont replies that this kind oftests should be carried out during the hardware commis-sioning and there are not under his responsibility. R. Bai-ley confirms that a few weeks are indeed allocated in thecommissioning schedule before the start-up with beam fora thorough machine checkout.R. Assmann asks if the application software will be testedby a dedicate team, independently from whom wrote thesoftware. M. Lamont replies that the manpower to do thatis not available. Thorough checks (basic functions, com-patibility, etc.) are carried out at the building phase.S. Peggs asks if, at the sector test, it will be possible tosimulate various stages of the LHC operation (e.g., energyramping) to properly check the applications. M. Lamontreplies that this will be the case (see next sessions).R. Aymar asks how much has actually been done on soft-ware development. M. Lamont replies that the project forthe LHC software development started about three yearsago. Considerable progresses have been made since then.Notably, the new proposed system has been already used atLEIR and will be adopted this year at the SPS. A detailedplan, with crucial milestones, is defined to make sure thatthe LHC requirements will be fulfilled.LHC Project Workshop - 'Chamonix XV'81

The Minimum Workable LHC: Plans ans Requirements for Beam Commissioning, Years 1 and 2 : Discussion, 2

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