Minutes of HERA Meeting      22.02.2005

HERA

• The integrated luminosity was 5.2pb-1, slightly less than last week due to scheduled and unscheduled breaks. The peak luminosity exceeded 4 10**31 cm-2 s-1 (4.8 10**31 measured by H1).
• Most fills had tolerable background conditions. The cause for the background oscillations seems to be orbit distortions at about SR 60m (BZ56SR correction coil or BU magnets). The BZ56SR power supply will be checked, electronics will be replaced.
• Some fills showed electron lifetime effects; short lifetime breakdowns, two extending for several hours. The long periods with reduced lifetime were not present with positrons.
• Last week there was no progress on polarization tuning.
• The cryo system failed on Sunday. One compressor unit tripped. The reason is not clear. The cryo permit was not removed due to some miscommunication. As a result the proton ring quenched.
  One octant (SR) is presently at 60K. The GO/GG magnets in the south and the ZEUS solenoid are cold again. The proton machine will hopefully be ready again tomorrow morning.
• The present plan is to do electron beam only polarization studies until the proton ring is back. 15mA are presently being ramped to check whether the electron orbit is fine with the proton dipole magnets being off. Polarization studies will be continued with higher currents. The plan is to finish one set of harmonic bumps and to do a BF (vertical rotator magnet) scan. It might be useful to ramp down the H1 solenoid.

ZEUS

• The data taking efficiency is quite good. The gated luminosity with all chambers on has passed the HERA I electron data sample.
• Background conditions improved significantly after the NEG regeneration last week. The proton background is now a factor of two below the prediction, the electron background about 30%. A clear improvement was also seen in the trigger rates. The spread was reduced. (This might be due to the proton orbit stabilization, which was on on the weekend.) Some considerable luminosity is lost when the slow collimator procedure is used. The luminosity seems to be less stable compared to H1.

H1

• The warmup and regeneration of NEG pumps was successful. The background went down by a factor of 1.5. On the weekend the HV could be turned on from the beginning, typically Ip=80mA, Ie=35mA. A similar improvement is needed in order to run at full beam currents.
• Fast spikes were also observed during the proton fill on Sunday. A 5s periodic structure was seen during collimator scraping.
• A change of the proton orbit is needed to optimize the acceptance of the Roman pots NL220. A 6mm orbit bump was already used in June, 10mm would be the optimum. This will be tried once we have luminosity again.
• The electron beam has to be steered in order to hit the laser of the LPOL cavity. Feedback to the BKR will be provided (new display with laser status and rate of Compton back-scattering).

HERMES

• HERMES is happy with the beam conditions, except of course the low polarization. Background rates are still asymmetric. The upstream orbit should be tuned.
• The electron beam dump triggered by the HERMES beam loss monitor (16.02. 21:34) was discussed.
  A rate signal and warning should be provided by HERMES before the beam abort threshold is reached.

Schedule

• The present plan is to do electron beam only polarization studies until the proton ring is back. 15mA are presently being ramped to check whether the electron orbit is fine with the proton dipole magnets being off. Polarization studies will be continued with higher currents. The plan is to finish one set of harmonic bumps and to a BF (vertical rotator magnet) scan. It might be useful to ramp down the H1 solenoid.
• Continue luminosity operation once the proton machine is ready.

• The next maintenance day will be Wednesday 9.03.2005 (not 2.03.)

                Uwe Schneekloth