Minutes of HERA Meeting 19.04.2005

HERA

• The exchange of the BU coils SR was finished on Thursday evening, faster than expected. There was some delay due to a leak in the proton vacuum system (the seal had to be replaced and repair of cables of temperature sensors). Proton beam operation started again Friday afternoon.
• HERA delivered 6 luminosity fills since Saturday. The electron current was reduced to 35mA. New files had to be made since the orbits had drifted. The proton background spikes disappeared. Some tuning is still necessary to optimize the conditions.
• Last night the proton aperture was limited NL (very small injection efficiency). The reason was the H1 VFPS, which was still in the beam position. The VFPS position should be included in the interlock.
• The collimator jaws to beam procedure will be used a few times before a new collimator file is made.
• Electron mirror tunes were tested during the night shift Thursday/ Friday. The beam was accelerated without problems.
• Another iteration of harmonic bump scan is necessary to improve polarization.

ZEUS

• During the weekend the proton background was about a factor of 2 higher than the expectation. One contribution was due to the poor vacuum in the section which was vented. The pressure and baseline background conditions improved yesterday after firing of TSPs. There are however still proton background problems which are not related to the vacuum. Conditions are fine for the present fill.

H1

• HERA delivered 6 fills. The integrated luminosity was 2.77pb-1, 2.28pb-1 on tape. The HV efficiency was typically between 60 and 70%. The first fill on Saturday was bad (HV efficiency 37%), the fill yesterday morning excellent (94%). The electron background was usually decreasing as a function of electron current. The proton current was sometimes increasing. The fast track trigger was still fluctuating a lot.
• A new water Cerenkov counter was installed after the filter, just before the luminosity calorimeter. The Cerenkov rates are available on the luminosity display.
• The electronics of the VFPS was not damage when the pots were left in the beam position last night. The VFPS position will be included in the interlock.

HERMES

• The target cell was exchanged last week. With the new cell the target polarization improved from 0.7 - 0.8 to 0.8 - 0.85. The so-called depolarization factor is however slightly lower (0.84 instead of 0.87).
• Data taking resumed without problems. Proton background was bad twice during injection. HERMES would like to be informed before the proton beam is scraped. The top/bottom rates should be similar.
• Higher electron polarization is appreciated.

Schedule

• Luminosity operation. Fine tuning of background conditions, optimize collimator positions.
  Increase beam intensities.

Shutdown Plans

• The machine group is proposing to start the shutdown in November in order to replace all remaining BU coils. Only half of the coils could be replace if the shutdown starts in August.
• The proposed dates are:
  • Start of shutdown 14.11.2005
  • End of shutdown 18.01.2006
  • Start beam operation 6.02.2006
• The plan is to have no further shutdown until the end of HERA operation provided the authorities agree on increasing the time between the interlock tests.
  Note added after the meeting: The Amt fuer Arbeitsschutz agreed on having no further interlock test after Jan 2006.
• A decision on the shutdown date will be made in the HERA coordination meeting in two week.

                Uwe Schneekloth