Minutes of HERA Meeting 20.09.2005

HERA

• The new vacuum chamber in the rotator section ER was installed on Wednesday. The seal at the absorber 4 electron flange SR11 was changed on Tuesday. NEG pumps in the south were activated on Wednesday. Beam operation restarted Wednesday to Thursday night.
• After two luminosity test runs a leak occurred in the rotator NR Friday morning. A welding seam at flange got untight. This was one of the few flanges in the rotator sections which had not been stiffened by an additional welding seam. The leak was repaired relatively quickly.
• Beam operation resumed again Friday afternoon. HERA delivered several luminosity fills over the weekend; proton currents of about 90mA, electron currents between 25 and 35mA. The vacuum in the south recovered very quickly. Presently, there are no current limitations from the vacuum. The temperature readings at SR14 were approaching the limit of 50 deg C. The reason is that the sensor had to be removed in order to replace the vacuum seal and were reinstalled with better thermal contact to the vacuum chamber. The temperature limit was raised from 50 to 60 deg C.
• The proton injection orbit was improved in order to reduced the background at HERMES.
• The coupling of the electron ring was optimized. Polarization tuning will start with an energy scan followed by the usual bump scans.
• The NEG pumps in the south may have to be regenerated next week depending on the vacuum and background conditions. The machine group would like to skip the maintenance day in October.

H1

• The detector is taking data without problems.

ZEUS

• The vacuum pressure recovered very quickly after the replacement of the seal SR11. At SR 8 - 11m the pressure is presently a factor 5 higher than before the leak.
• Data taking started again on Saturday with good efficiency. The backgrounds are already similar to the extrapolation. The influence on the trigger rates is minor. The proton lifetime has been good. The effect of the high pressure ER is seen in the electron background rate. The beam currents are not limited by the background conditions.
• The CTD is operating stably. The problems observed last week did no reappear.
• The TSP pumps should be fired regularly. It is not clear whether the NEG pumps have to be regenerated next week.

HERMES

• The proton background was high during luminosity running on Monday.
  On Sunday the vertical position of the electron beam had to be changed in order to reduce the background. The old settings worked fine for the following fills.
• A luminosity scan will be done at the end of the next fills.
• In case of a break, HERMES would like to have temporary access.
• There is a big disagreement between the transverse and longitudinal polarimeters. It is not clear which measurement is correct.

Schedule

• Continue luminosity operation. Increase electron current.
• Polarization tuning will be performed during luminosity operation.

                Uwe Schneekloth