Summary notes of the forty-seventh meeting of the LHC Commissioning Working Group

Summary notes of the forty-seventh meeting of the LHC Commissioning Working Group

Tuesday June 10^th, 14:00

CCC conference room 874/1-011

Minutes of the Previous Meeting and Matters Arising

Roger explained that several LHCCWG members were absent due to other parallel events, in particular an audit of the BLM system. There was one comment on the minutes of the 46^th meeting, received prior to this 47^th meeting. Namely on the issue of transfer function and magnetic model Luca Bottura had clarified by email that his team was including all known and measured effects in the transfer function models they were providing. Luca was also compiling a table of estimated modeling accuracy, which Rob Wolf would present at an upcoming LTC. Luca’s team had discussed with Mike and Marek the use of the integral transfer function and magnetic length, and the present mechanism was designed consistently, i.e. it “should” provide the expected correspondence to the MAD optics. Intensive testing of these models was recommended nevertheless. Jorg remarked that he had obtained the same answer from Walter, namely that all data were renormalized to the magnet length listed in MAD.

LHC Status (Roger)

Roger announced that this was the first time that the whole machine was either cold at 2 K or being cooled down. The target date for closure of the experiments and caverns had slightly been shifted, to the end of July.

The powering tests in Sector 78 were 80% complete, the dipoles had been ramped up to 7 kA, and almost everything was commissioned in this sector except for the triplet. In Sector 56 a dipole training campaign had been ongoing through the whole of May. There were about 30 quenches in total, and a current of 11.12 kA had been reached. The rate of current increase was much lower than expected from SM18 data. In the ICC meeting of the previous Friday, Ezio had reported how the magnet people were refining their model. The slow progress at high magnet current was explained by a loss of memory for a fraction of the Noell magnets. Methods to speed up the quench training were under study.

On Friday, during a regular training quench and quench propagation to the neighboring dipoles, a “symmetric quench” had been observed, i.e. the quench was symmetric between the two apertures, while the magnet current was ramping down, possibly revealing a hole in the QPS. Oliver pointed out that on the ramp down not all the quench signals were being looked at.

Continuing his LHC status summary, Roger reported that the training campaign in Sector 56 had now been stopped, and that there would be only a limited training campaign in Sector 78. One of the consequences of the stop of the training effort in 56 was that work on the beam-dump dilution kickers would happen this week, and should be finished by its end. Lyn would soon make a decision on other interventions, e.g. on the water cooling intervention (in a few weeks time), and on cryo-electronics work in Point 8. Sector 56 would be available for operation in the following week. Gianluigi and others would develop a test & study plan this sector.

Gianluigi remarked that one item to study could be the impact of possible limits on the “current acceleration”, d^2I/dt^2. Stephane recommended to perform a dry run of the squeeze including all trim quadrupoles and all sextupoles and thereby also to enhance the sensitivity to the acceleration limit. He warned that 10 minutes had so far been foreseen for the squeeze, but with the new limits the time needed might be significantly longer. The limits were likely to come from the trim magnets and the lattice sextupoles. Alick recommended to reserve independent console space for OP commissioning.

Roger reported an issue with the strengths of the triplets in Points 2 and 8. Oliver clarified that this was a problem of the power converter and not of the magnets: the installed power converters could not reach the nominal current of these triplets for the injection optics ramped to 7 TeV. The maximum magnet strength had been specified as 230 T/m, and a reduced upper value of 200 T/m limit had been set for high radiation, which is not expected in these two points. The reason why a field above 200 T/m was needed when ramping the injection optics to 7 TeV was constraints on the phase advance between the kicker and TDI at injection. If there turned out to be a problem with the strength, one could always change the optics before, or on, the ramp; otherwise it would be varied prior to the squeeze at top energy. Oliver recalled that this problem had been brought about by the decision to use the TCLI collimators. Paul clarified that the power converter problem was related to the DCCT and not to the number of converter modules. Frank remarked that in any case this was not a problem for the 5 TeV run. A response was that the optics will be commissioned up to 7 TeV in 2009, and one should try to explore its feasibility in 2008.

MPS Commissioning (Jorg

)

Jorg explained that the MPS commissioning may be split into two parts: a technical commissioning of all interlock systems, and a beam commissioning where correct settings will be established. He concentrated on the first part in this presentation.

Answering to a question by Roger, Jorg confirmed that he had recently been put in charge of MPS commissioning, at least for the period prior to beam commissioning, and perhaps for afterwards as well. He underlined that he would need a lot of help to do this job.

Jorg showed that the BIS comprised two parts: the BIS core and all connections. For the BIS, a user connection test was in progress. At the beginning of July the core would be ready, fully commissioned by Bruno Puccio’s team. From then on, one could hook up systems and perform independent tests. One major input to the BIS is the powering system (representing more than 50% of all interlocks). One distinguishes between maskable (for safe beam) and non-maskable interlocks. The powering interlocks themselves comprise sc magnets (most sub-parts of which are checked during HWC), the powering interlocks for nc magnets, and the magnet current monitors. PIC tests require that 2 adjacent sectors be available and reserved for the tests. The powering interlock effort is driven by Markus Z., Alvaro, et al. Checks must be performed that the logging is correct, and test results will be documented in MTF. For PIC 4 days in total were needed. Every day a different pair of sectors could be commissioned. As soon as 7-1 and 8-1 were ready, one could start to commission the first two sectors.

Roger asked whether the hardware commissioning activities would care about the magnet current monitors. Jorg replied that the FMCMs were not yet commissioned.

Jorg continued his tour of MPS commissioning, where the next item was the WIC – for which the same exercise was performed, going through all converters. The WIC and FMCM commissioning could be done at the same time, on the same day for pairs of two sectors. This would make sense as the same people were involved in both. One should use the sequencer to support this activity.

The next big component of the MPS to be commissioned was the vacuum system. Vacuum valves in one octant can only be opened when proper conditions are fulfilled (magnets cold etc.) The commissioning of the vacuum system is being followed up by Gianluigi. Several details were still to be defined, e.g. should everything be checked, or would random sampling suffice, or should we plan for a mixture (testing everything in the first sector and taking random samples later)? These questions were delegated to Gianluigi. The vacuum MPS commissioning would have to wait until the BIC was ready, i.e. until the end of the BIC reliability runs. There were 24 connections from the vacuum to the BIC per IR.

Stefano pointed out that the need to wait with MPS commissioning for the BIC was a general problem also for other systems. Gianluigi remarked that other items to be checked for the vacuum were logging, post-mortem, and alarms. He would try to get the alarms ready for the time of interlock checks.

Alick stated that each of the user systems should be aware of the consequences of switching a flag to “false”. Jorg cautioned that there were some inconsistencies and differences between various user systems. Replying to a question, Gianluigi explained that there was a vacuum-system logging for each change of state of a valve. Roger commented that this general effort continued the work of Jan and his subWG. Jorg agreed, adding that in many cases a well defined procedure existed, but for some cases not or not yet.

The next MPS item was the collimation system. The collimator interlocks included position and environmental parameters. Settings and test had been defined and would start soon. These efforts were driven by the collimation team.

Oliver, referring to Ralph, asked whether the collimation should be part of the MPS system or not. Ralph agreed with Jorg’s approach, elaborating that the system was designed as a cleaning system. Responding to a question by Frank, Jorg explained that the term “environmental parameters” alluded to items like the temperature of the jaws. Ralph commented that an automatic function was developed by Stefano which would drive the various interlocks, and log the BIC response at the same time.