Minutes of HERA Meeting 19.07.2005

HERA

• HERA delivered 5.5 pb-1. The specific luminosity was 2 10^30 cm-2 s-1 mA-2. The efficiency was poor due to major technical problems. Proton background spikes are still present, caused by problems with the GA circuit.
• The main technical problem was a grid-cathode short in the main RF amplifier in the 208MHz system D. The work was identified on Saturday. A temporary workaround as implemented on Sunday. The amplifier was replaced yesterday. The system is not yet properly matched.
• The so called GA proton background spikes reappeared. The spikes were traced to a problem with GA power supply in the north. A spare power supply exists, but is not yet available. Installation will probably take one day. In case GA spikes continue to be a serious problem, the power supply should be replaced as soon as possible. It should be checked whether the August maintenance day (3.08.) can be moved forward.
• The maximum polarization was 50% in collisions. During a typical fill, polarization started at 30% and increased to 45% towards the end.
  56% was obtained with electrons only.
  All harmonic bumps including 2nd order were scanned. Some higher order bumps were scanned last week without any improvement. The energy was rechecked (same result as before). The most sensitive bump was rechecked (same value as before).

H1

• The normalized track trigger rate is close to the expectation. For some recent fills it was slightly higher due to proton spikes. The HV efficiency was 75%. The main loss was due to GA spikes.
• The integrated luminosity written to tape was 3.8pb-1.
• The positions sensors indicate a horizontal movement of the GO magnet with respect to the bridge (horizontal rotation). Steps are observed after maintenance days. The displacement amounts to 1.5mm since January.
  The GO will be readjusted with beam in the machine.
• The photon position in the luminosity monitor is still at 1.5cm. It should be moved back to the nominal position.
• The proton orbit should be changed in the vicinity of the VFPS to improve the acceptance.

ZEUS

• The background conditions were relatively bad, usually on top of the prediction, although a factor of 2 lower is possible. In addition, GA spikes have been causing HV trips. The GA power supply should be replaced as soon as possible if the spikes continue.
• Over the weekend, the data taking efficiency was poor due to trigger problems, which are solved now. The increased rate of off-momentum electrons turned out to be a trigger problem. Some collimator positions were readjusted on the weekend, while trying to understand the off-momentum electron rate. The background improved slightly. Collimator optimization should be repeated regularly.
• The integrated (e- p) luminosity is a factor of 2 higher than last year (e+ p). HERA has surpassed the HERA I integrated luminosity.

HERMES

• Background conditions were correlated with the electron lifetime. Turning on was difficult when the lifetime was less than 1 h.
• High background rates (up to several MHz) were seen during proton injection.
  F.Willeke remarked that this was related to the proton RF problems. Trips of pre-amp were causing large energy spreads.

Schedule

• Continue luminosity operation with increasing electron current.
• Continue polarization tuning.
• Prepare spare GA power supply. The maintenance day might be moved forward.

                Uwe Schneekloth