Minutes of HERA/Experiment Coordination Meeting  15.03.2005

Agenda

• Brief status reports HERA and experiments
• Shutdown plans
  Status and milestones of shutdown preparation
  • Spare magnet situation
  • H1 FST/BST repair
  • ZEUS STT repair
  • HERMES Recoil detector
    Shutdown dates
• Schedule and operation

• Date of next meeting
• AoB

Minutes:

F.Willeke: HERA Status

• The proton bunch current (8.3 10**10 p/bunch) is limited by the injector chain. The electron current has not increased anymore since 14.02. due to technical problems with the RF system and operational issues. The plan is to increase the electron current and eventually switch to 180 bunches.
• The specific luminosity is slightly reduced. The peak luminosity has not increased anymore. The reason is larger proton emittance (the DESY III intensity is not reduced anymore), larger proton beam blow-up and more attention paid to operational issues. There is now better agreement of the H1 luminosity measurement and the calculation from beam parameters. The H1 measurement dropped by about 12%. Luminosities of 4 - 4.5 10**31 cm-2 s-1 (specific luminosity 1.8 - 1.9 10**30 cm-2 s-1 mA-2) are possible with good optimization. L=5 10**31 should be possible this year.
• The operational efficiency was poor in January, it improved in February, but decreased again in March due to the recent cryo problem. The statistics is dominated by technical faults. The biggest problems were cryo system and magnets. The large effort spent on the maintenance of the power supplies has paid off.
• The total delivered luminosity is 42pb-1 as measured by H1. Luminosity production was up to 6pb-1/week, almost 1pb-1/day, although the average is only 0.5pb-1/day. The average luminosity per day is significantly higher than in 2004.

• The background conditions from halo protons are presently more critical than in 2004. The reasons are higher luminosity, smaller electron size, less beam-beam blow-up of electrons and higher sensitivity to small effects.
• The measures used against background spikes so far are comprehensive diagnostics and maintenance of magnet power supplies, using alternate collimator jaws, proton orbit stabilization, lengthy collimator adjustment procedure, beam scraping and frequent orbit and collimator tuning.
• Spikes are probably due to damaged a BU coil SR (winding fault), although there is no prove yet. Orbit analysis indicates that the source for orbit distortions is at about SR75. The plan is to exchange the BU coils SR in the summer shutdown.

• Frequent sudden reduction and recovery of the electron lifetime is observed now. This can only be explained by dust trapping. The probability for lifetime breakdowns is expected to increase if the number of bunches is increased.
• Previous studies indicate that there is a narrow band of stability for trapping dust particles in the beam. Fortunately, the probability is not too large.

• The failure of the cryo plant a few weeks ago was discussed. Presently, there is no redundancy if one compressor fails. The north compressor will be upgraded. The TTF compressor will be brought into operation.
• The first new spare BU coils will arrive in May, in spite of problems with the delivery of copper. Most of the coils needed for the shutdown (12) will be delivered in July and August.
  The present plan is to exchange all coils in the SR straight section. There is no decision yet which other BUs will be repaired.

• In general, machine operation is quite smooth. Problems with operational mistakes occur in case of large deviations from routine operations, e.g. after long breaks.
  Recently, there were problems with the orbit stabilization procedure, resulting in high temperatures NR.
• Last Monday a leak occurred at the SR11 absorber 4 electron flange 2 minutes after an electron beam dump. No unusual heating of the beam pipe was observed. The leak was fixed by tightening the flange. It may reappear in the near future. Replacing the seal, including warm-up and cool-down of GO/GG, would take about 2 days.
• The support for some components (quench protection, PETRA, proton RF) is critical. The improved maintenance of power supplies has been very successful.
• The further plans are: keep increasing beam currents, increase luminosity production and continue to make operating more efficient.

M.Vogt: Polarization

• The electron polarization achieved so far is 35-40% (50-55%) for colliding (non-colliding) bunches for positive helicity and 30-35% (50-57%) for negative helicity. The expected polarization without beam-beam effects is 57%. The helicity asymmetry, which was present for positrons, has disappeared.
  A major step during the polarization studies was lowering the vertical tunes. The 1st and 2nd order harmonic bump scans had to be reiterated in March. Conditions were sometimes unstable during the first round of bump scans. The operational procedures were improved. Bumps are now included in the lumi files. Continuous monitoring is needed.
  The best beam energy is 27.628 GeV.
• The largest problem is lower polarization for electrons wrt to positrons due to beam-beam effects. Last year the polarization of all bunches was typically 35-40% for positive and 40-50% for negative helicity. With electrons on protons the tune shift is positive. Colliding bunches have higher tunes. Polarization is however larger for small tunes.
  Larger polarization is therefore expected with so-called mirror tunes. This requires a complete new set of electron files. The injection and luminosity optics files are already finished. The intermediate file still has to be done. Several effects have to be studied. The time estimate for tuning up operations with mirror tunes is at least one week. A "quick or dirty" test can be done in about two days.
  The mirror tunes will again be discussed in the HERA meeting in 2 weeks (29.03.).
• The beam beam experiment, dumping the proton beam instead of a high density end of fill run, and setting the non-colliding tunes to the incoherent tune of the colliding bunches should be repeated.
• The rise-time fit and manually triggered TPOL average are very useful during polarization tuning.
  The cavity LPOL saw first Compton events.
  The depolarization kicker should be commissioned as soon as possible.

W.Zeuner: ZEUS Status

• The detector is working fine, taking good quality data. The integrated luminosity is already larger than for the 1998/99 running period. About 39pb-1 have been delivered until today. With good background conditions the data taking efficiency (all HV on) is typically above 80%.
• In general, background conditions are fine, although they vary from fill to fill. Minor spikes do not harm when the proton background is low and stable. For some periods the proton background is very high, baseline too high and large spikes. More efforts should be spent on background tuning.

• Preparations for the STT removal tool are making good progress. The design is almost ready. It was discuss with the machine group. There were no objections. Fabrication of the parts is in progress. Test assembly and tests with a dummy load are planned for May.

• The leak at the absorber 4 electron flange was discussed extensively. The interaction region would have to be vented with nitrogen in order to exchange the seal. ZEUS would not be able to take data for several days.
• The decision was not to exchange the seal tomorrow. In case the leak re-occurs it will be repaired by gluing. The seal will then be replaced during the next maintenance day.

M.Klein: H1 Status

• So far HERA delivered 40pb-1, 35pb-1 have been written to tape. Only 15pb-1 are with CJC1/2 HV on due to poor background conditions. The proton beam gas background improved considerably after NEG pump re-generations. The HV efficiency improved to 60-80%. After the warmup of GO/GG tomorrow the background level will hopefully permit to operate at design currents.
• The stability of HERA operation is a major concern. There were many failures last week. On Sunday the GG shield temperature increased to 90K, resulting in a very poor vacuum. H1 had to turn off the chamber HVs.
• Timing information of the track CJC fast track trigger and the backward ToF is now used to study spikes.

• The silicon repair is making good progress. The new Analog Pipeline Chip was delivered to Zeuthen. First tests are very promising. Repeater electronics was ordered. Wafers were delivered, acceptance tests are in progress. All APCs and decoders were removed from the BST. 5 have been re-equipped for test bonding. Delivery of hybrids failed. As a consequence, the BST will be rebuilt before the FST.
  The silicon detector is expected to the ready for installation in early September as planned.

P.Di Nezza: HERMES Status

• The goal of 7 million transversely polarized DIS events will only be reached in 4 years of data taking instead of 2 years. The end of fill high density running is very successful. Unfortunately, the beam polarization is still low.
• The target is fully operative. Polarization and atomic dissociation are high, 80% and 90%.
• The beam loss monitors were installed to protect the lambda wheels and target cell. The baseline signal is well below the threshold. The electron beam has been dumped a few times per year.
• In general, background conditions are reasonable. The proton background is good even when H1/ZEUS request beam scraping. Occasionally spiky proton background does not affect data taking.
• Requests:
  • The electron current should be increased.
  • More effort should be put on beam polarization.
  • BKR messages should be less random.
  • There are serious problems with the target cell temperature if the beam was kept at 12 GeV for a long time.
• Test installation of the recoil detector is making good progress. Cosmics will be taken in April and May. The time estimate for installation is 7 weeks.

B.Zihlmann: Polarimeters

• The TPOL has good performance and efficiency. There were only minor problems. Dosimeters were installed behind the preshower detector. Offline analysis studies are in progress.
• First Comptons were seen in the LPOL cavity. The LPOL sandwich calorimeter was used. Parts for the new calorimeter were ordered. Installation is expected in June.

Schedule

• Maintenance day tomorrow:
  • End luminosity operation at midnight. Start warming up GO/GG magnet north and south.
  • Some proton machine studies (tune control during ramp) until 06:00hrs.
  • Regenerate NEG pump tomorrow. Cool-down GO/GG again.
  • Resume luminosity operation Thursday morning.
• The April maintenance day is canceled.

• The rotator positions (all rotators) will be changed in early April.

• ZEUS is the coordinating experiment.

Date of next meeting

Uwe Schneekloth