Minutes of HERA Meeting      30.04.2002

HERA

• After the machine shifts, the electron machine is in good conditions, in particular with the H1 and ZEUS solenoids turned off. Some tuning is still necessary with the solenoids on. Beam based alignment studies were done at injection and full beam energies, resulting in a vertically flat orbit left of the interaction points.
• In general, the vacuum conditions improved after the beam bake-out. A pressure increase was observed in the north IP (maximum at NR6) at currents above 10mA. The maximum current at injection energy was 32mA. At 30mA the pressure is at the limit. The H1 radiation monitor measured very high rates. 22mA were accelerated, but lost at 21GeV (The files were with solenoids turned on, which were off at the time.)
• Collisions (30 proton, 36 positron bunches) were achieved on Saturday and Sunday. The procedures are now well established. The specific luminosity measured by ZEUS was 1.15*10**30 cm-2s-1mA-2, in agreement with H1. It was constant over many hours, i.e. there is no growth of the proton beam emittance. The proton background was very high. Tune modulations could cause a large proton halo. The main power supply was checked. The GJ magnet power supply shows a large voltage ripple (being checked). The proton beam lifetime during collisions is now typically 30 hours. In 2000 typical values were 100 hours. The beam heights might not be matched properly.

ZEUS

• During collisions the forward/rear tracking detectors and the MVD were turned on on Saturday. The CTD could not be raised to full HV. A special positron beam only run was taken with CTD at full HV after the proton beam was lost.
• On Sunday the CTD was at full HV for 7 minutes, but tripped repeatedly because of high proton background.
• High backgrounds were observed by the MVD radiation monitor during the bake-out of the electron machine Sunday to Monday night, corresponding to 300-500rad. (The injection efficiency was poor.)

H1

• Saturday afternoon the positron gated background was reduced by a factor of 4 by optimizing the beam orbit. The chamber current was still high at 75% of the nominal HV.
• On Sunday the CJC1 and 2 chamber currents were reduced from 50 to 12uA and 70 to 18uA, about 5uA higher than without beam. Moving in the collimators at NL6m increased the background. The photon beam in the luminosity monitor was about 1cm too high.
• Would like to go to positron currents of 10 to 12mA.

HERMES

• The positron beam conditions were very good on the weekend. The proton background was more than a factor of 10 higher than in 2000. The beam was used to commission the detector.
• Would like to increase the e+ current to 10 to 15mA.

HERA B

• The target wires were operated for the first time. Saturday afternoon all 8 wires were inserted one by one without problems.
• Initially, background conditions were good Sunday morning. Later on the background was 2-3MHz without target (a factor of 100 higher than on Saturday). A beam halo of +-10mm was observed. Data were taken. The interaction rate of the 3rd bunch train was significantly higher.

Schedule

• Continue colliding beam operation: positron beam of about 15mA, small proton beam current. Optimize background conditions. At the end of a luminosity fills one of the beams will be dumped in order to studied the background conditions with single beam only.
• Electron machine bake-out will be continued at night with proton beam present.
• Luminosity scans will be performed on Thursday.
  

  
  

• ZEUS is the coordinating experiments.

Miscellaneous

There was a discussion how to improve the communication between the shift crews of HERA and the experiments.

• The run-coordinators should attend the weekly "Kuemmerer" meetings Monday at 15:00hrs and the daily shift change meetings at 14:15hrs in the HERA control room (at least at the beginning of their terms).
• A video link between the HERA and experimental control rooms was proposed.

                Uwe Schneekloth