Minutes of HERA Meeting      11.11.2003

HERA

• The reason for the venting of the north interaction region last Tuesday is understood. The proton beam was lost due to a failure of a proton quadrupole magnet (GA magnet) power supply. At the time of the beam loss the proton optics was not in a well defined state (error in file system), resulting in a very fast beam loss (within 4ms). The sampling time of the quench protection system is 5ms and hence did not fire the beam abort system. The main beam loss occurred at NL11, where the IR vacuum chamber splits into proton and electron beam pipes. Thermal and mechanical stress caused a leak at the proton flange NL11. The seal was exchanged. The vacuum pressure recovered relatively quickly to 10**-9mbar.
  Several measured are being discussed to prevent similar accidents: Increase the sampling time of the beam loss monitor system (decrease integration time by a factor 5). Measure beam current losses. Use scintillation counters. The beam position monitor information is not reliable enough.
• During the access, the vacuum seal at the electron beam pipe flange NR11 was replaced by a Nb seal.
• Beam based alignment showed significant magnet offsets in the north IR. Magnet positions were corrected during the access. After the re-alignment the magnet currents changed as expected.
• HERA continued with luminosity operation with low beam currents. TSP pumps were activated frequently.
• NEG pumps in the north IR were regenerated yesterday.
• High temperatures, observed at absorber 4 (SR11), did not occur at the large flange towards the IP, but at the proton beam flange. This is caused by direct synchrotron radiation. The positron beam dump last night was caused by a false temperature alarm. The alarm system will be improved to be less sensitive to noise.
• MKK is trying to improve the reliability of power supplies.
• A new procedure was prepared to correction the dispersion. This should result in a better match of the beam sizes at the IP.

H1

• Sunday to Monday night the background conditions were rather high (mainly synchrotron radiation). Last night the chamber current was a factor of 3 less. Maximum beam currents are 20x30 mA**2.

ZEUS

• A new tool for background optimization is available. The CTD current is displayed together with the expected current calculated from the proton and positron gated C5 rates and the beam currents.

HERMES

• Running conditions were fine last weekend. The upstream beam orbit has to be improved at higher positron currents. The positron current should be increased.
• Trips of several components (turbopumps, cryopumps) have been observed during proton acceleration.

Schedule

• Continue luminosity operation with 120 bunches. Proton current around 10mA, try to increase positron current as much as possible.
• Correct beam dispersion.
• Polarization studies.

• Operation Dec/Jan: End beam operation 23.12.2003 07:00hrs, switch off components during day shift. Start switching on Monday 29.12.2003 07:00hrs. First beam operation 29.12. evening or night shift.

                Uwe Schneekloth