Minutes of HERA Meeting 17.05.2005

HERA

• Last week operation was very successful. HERA delivered 8.2 pb-1, the best week so far. A new luminosity record was achieved 5.07 10**31 cm-2 s-1. The efficiency was 62%, polarization up to 40%.
• The only serious technical problem was a leak at the TPOL exit window on Saturday. An orbit displacement of 3mm, which was part of the dispersion bump, lead to local heating and a crack in the window due to increased synchrotron radiation. The window was exchanged Saturday morning. Luminosity operation resumed in the afternoon with reduced electron current.
• There has only been slow progress in increasing the electron current. It is not yet limited by the number of bunches.

• It is difficult to achieve much higher polarization with the present procedure. Polarization should be well above 40% with mirror tunes. High polarization should be obtained faster during a fill.
• After some discussion it was decided to spent 2 days of the machine studies on mirror tunes immediately before or after the next maintenance day (1.06.) Depending on the results, HERA will then go to mirror tunes or back to the present conditions.
  The position of the spin rotator will be changed 1.06.

ZEUS

• In general good running conditions. HERA delivered 8.16pb-1, excluding lumi tuning. 6.84pb-1 was written to tape (HV on). May 12 was a record day: 1.67pb-1 delivered, 1.25pb-1 on tape.
• The background was almost always below the parameterization. There were relatively few HV trips.
• The specific luminosity measured by ZEUS and H1 have slightly different slopes.

• HV trips are much less frequent after the BU repair, high dead time caused by high First Level Trigger rates is now seen more often. There is a strong correlation between FLT input rate and dead time. The dead time is less than 5% for 300Hz input rate, it grows to 10% for 400Hz.
• The FLT rate has a strong anti-correlation with the proton lifetime. Above 100hrs rates are stable. Below 100hrs the FLT rate increases dramatically. The most sensitive trigger is the charged current trigger.
• The CTD current and C5 rate cannot always be used to optimize the FLT rate. The best parameter found so far is the proton lifetime.

H1

• Good luminosity running. Congratulations to HERA for successful operation. The luminosity written to tape was 6.3pb-1. The main loss of efficiency was due to HV trips. The HV efficiency was usually above 70% (average 77%).
  The fast track trigger rate was close to the expectation.
• Similar to ZEUS, trigger rates increase significantly when the proton lifetime is below 100hrs.

HERMES

• In general good conditions. Some fills had increased background after the vacuum leak on Saturday. The last fill was fine.
• The beam position and tilt was varied slightly. The vertical tilt should not be higher than the 'best value'.

Schedule

• Continue luminosity operation.
• 2 days of the machine studies on mirror tunes immediately before or after the next maintenance day (1.06.)
  The position of the spin rotator will be changes 1.06.
• Note added after the meeting (18.05.):
  • Last night a leak occurred at a welding seam NR14. The leak was fixed by glueing.
  • The position of the rotators was changed this morning.
  • HERA will start the mirror tune studies today, since high current luminosity operation will not be possible until the vacuum NR has improved.
  • NEG pumps have to be regenerated, probably on Friday (not decided yet).

                Uwe Schneekloth