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

 

Tuesday June 10th, 14:00

CCC conference room 874/1-011

Persons present

 

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 46th meeting, received prior to this 47th 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.

Next in line was the beam dump system, for which tests were ongoing during the dry runs. In the LBDS everything was related to MPS. A specification for the Integrated Systems Tests (ISTs) was available but the MPS specifications were almost empty. Another concern was that the beam energy tracking system (BETS) had a lot of external inputs, and BETS tests could only be performed when all energy sources were connected.

Jan commented that one could use the MB signal from one sector, and split it, for partial commissioning. It might be necessary to do first tests with such a simplified configuration.

The beam loss monitors are another special system. Here the IST and MPS tests were basically the same, but the IST specifications appeared to be in better shape.  Jorg made the proposal to replace the MPS specifications by IST specifications. He also pointed out an unusual split of check tasks, a point which he would follow up after the BLM audit was finished.  Jan commented that one could perform an automated test after every fill to test the BLM functionality. However, the scope of the automatic tests would need to be defined, and a lot of question marks remained.

Screens and mirrors came under the heading BTVs. Their interlocks will be commissioned as soon as the BIC connections were ready. The commissioning could be facilitated by re-using automated test software from the SPS transfer lines developed by Jorg, and Rossano was pursuing this.

Now turning to the experiments, here several categories existed: magnets, movable detectors, ‘emergency dump’, and injection inhibit. Some question marks pertained to the readiness of TOTEM. Alick had volunteered to follow this up.

Roger asked whether the “beam emergency dump” was linked to the beam condition monitor. Jorg replied yes.

The injection system comprises vacuum, BLMs, MKI, FMCM, and collimators. This system was a relatively modest effort, and partial tests had been done during dry runs already.

Other systems included operator button (Bruno and BIS team), aperture kickers, injection kickers, beam position in IR6, rf & transverse feedback (only rf cryo for startup), beam current monitor, and access system.

Alick posed questions about access safety and the LBDS. Jorg answered that there was a direct and an indirect link from the LBDS to the BIC.

Roger inquired if there was clear definition of what can and can’t be masked. Jorg replied yes.

Mathias expressed some surprise that there was no rf interlock, pointing out that a debunching beam might compromise the machine safety. Frank remarked that a debunching beam should be detected by the abort gap monitor. However, Jorg and Rhodri replied that there was no connection from the abort gap monitor to the BIC at the moment.

Jan commented that the aperture kicker was maskable, but that it was supposed to be operated with safe beam only.  Jorg further elaborated that indeed the interlock for the aperture kicker key could be masked, and that this mask was taken into account only for a safe beam.

Jorg continued his presentation looking at the SIS. The SIS would produce 4 signals: injection inhibit for beams 1 and 2 communicating with the injection BICs, the beam dump of both beams connected to the CCR BIC, and some alarms. The plan for the early commissioning period was to keep the SIS interlocks at alarm level and to see how they work, before activating them, since there was a lot of software behind. In particular, the SIS signals were not yet sent to the BICs to avoid interference with the BIS. Concerning the SIS commissioning, Jorg recalled that the SIS included the 800 cold orbit correctors which were not treated in the PIC and which could trigger an injection inhibit. Their interlock test could be automated with a sequencer. Other groups of items which are part of the SIS are the BTVs, the integrated fields of the CODs, the current limits on separation dipoles & MCBX, the RF cryo system, as well as energy & intensity limits. Jorg naturally was in charge of the SIS MPS commissioning.

Oliver asked whether other types of test would also be done, e.g. try to fire an injection kicker after an injection was complete, that is to do something that should not be possible and see how the system reacted. Gianluigi remarked that the injection was immediately inhibited, as soon as one went out of the allowed energy window. Jorg commented that many similar items were described in the procedures. Frank asked about the relation of BIS and SIS. Jorg explained that the SIS was a software input into the BIS. Oliver asked whether one also verified components protection, e.g. against driving rf cavities through resonance. Jan replied that the rf frequency was part of beam dumping system. There also was an RBAC limit preventing certain potentially harmful actions. It was recalled that the momentum limits imposed by the beam dumping system were tighter than the ring acceptance. The RF voltage was monitored too. Frank commented that maybe the cavity tuning could be an issue as it had been in HERA.

Ralph remarked that no procedure was prepared for measuring chromaticity or dispersion, where the collimators would have to follow the off-energy orbit shifts. Jan or Ralph S. replied that this was not a problem for chromaticity as one needed to modulate the orbit by microns only, in which case the collimators would not need to follow the beam motion presumably. Concerning dispersion, it could be measured by injecting a single bunch and measuring dispersion at injection.

Summarizing his presentation, Jorg stressed that the MPS commissioning would start soon, at the beginning of July, when all BIS connections as well as major systems (powering, collimation) would be ready. Some clarifications were still needed for the BLMs and LBDS procedures. The commissioning of the “safe machine parameters” was yet to be defined by the BIS team and Alick.

Jan asked about the documentation of the tests and the demonstrated performance. Jorg answered that some systems, e.g. powering, would record the test information automatically in MTF; for others this was not defined. Alick commented that choosing a method of documentation was left to the user systems, and MTF might be an option. Roger remarked that this was part of a more general question.  Paul commented that MTF required EDMS, which was not guaranteed to be always available. Rhodri added that EDMS, however, was a convenient tool for describing a system state and for signing off.

Jan pointed out that if one did not make the documentation effort now, probably one would never do it. Rhodri stressed that a track record of MPS tests would be important. Jorg said he would organize discussions on this topic over the next days.

Next Meeting

Tuesday June 17th, 14:00

CCC conference room 874/1-011

Provisional agenda

 

Minutes of previous meeting

Matters arising

TOTEM Roman Pot Operation at the LHC (Ernst Radermacher)

Sector 56 – preliminary test plan (Gianluigi)

AOB

 Reported by Frank