Summary of operation last month

Luminosity operation has become more stable. The efficient is not yet 50%. The proton current is typically 20mA. The positron current at injection has been increased from 20 to 30mA. The specific luminosity at H1 is up to 2.3 10**30 cm-2 s-1 mA-2. At ZEUS it is 1.7 to 1.8 10**30 cm-2 s-1 mA-2. This difference cannot be explained by differences in the beam optics. Some decrease of the specific luminosity is expected as the bunch intensities are increased.
No significant improvement of the vacuum at the IRs was observed last month. The temperature of the GO/GG beam pipes was increased from 50 to 110K a month ago. Operating the magnet with beam pipes at room temperature did not work. In the south IP the magnet already quenched at 25A. At H1 a quench occurred at 300A. Last week the temperature (GO/GG at H1) was raised to 170K. It is not clear whether the decrease of background observed in October was due to the change of beam pipe temperature or the regeneration of NEG and Ti pumps. It is planned to go back to 55K. Regular operation at increasing positron current is still necessary to condition the vacuum system.

Summary of last week

During luminosity operation the average positron peak was 27mA.
Wednesday TSPs were heated NR to study the sensitivity to the proton beam gas background.
Monday there was an access to check the connections of the GA and GB magnets and for work on the electron cavities. A few loose screws were found and tightened on the magnet current bars. This is should not be a problem until the shutdown. New washers will be put in in the shutdown. Another cavity west left showed a similar behavior as the cavity which had a defective plunger a few weeks ago. The plunger was exchanged. No damage was found. The cavity cooling was improved.
There were some beam losses due to the failures of the superconducting RF cavities. A ceramics window has to be replaced.
The source of background spikes is being studied. Proton spikes seem to occur in the east left section, which could be caused by a defective magnet. Instabilities of electron dipole are observed.
Last night proton machine studies were done, which were scheduled for today.
Timing problems, the input signal for the positron RF disappears for 1 mus and confuses the trigger, are still occurring. The components are quite old. An upgrade is being discussed.
F.Willeke proposed to have one high current fill to make sure that there are no problems operating at high currents and to achieve high luminosity.

Preparation for the shutdown

It is presently unclear what modifications of the vacuum systems could be done to decrease the pressure at the IRs significantly. The conductance of the pumping ports can be increased. Installation of a cryo pump close to the IP is in preparation.
The design of the new GI magnets is ready. It was decided not to build new magnets.
Realignment of the IR magnets (lowering) is being considered.
Thermal desorption of the GI/GJ beam pipes and the effect of low energy, wide angle synchrotron radiation photons is under study.

The total delivered integrated luminosity is 4.5 pb-1. The collected luminosity is 2.5pb-1 (H1 active), 1.0pb-1 (HV on). It takes some time time until the chamber HV can be turned on. For last month there is no significant improvement of the vacuum pressure and CJC current during ep operation. A factor 5 improvement is still required for running at design currents. The base pressure (proton beam only) has improved after regenerating NEG and Ti pumps. It is not clear whether there was any correction with the GO/GG beam pipe temperature. The proposal is to decrease the temperature again to 50K.
A comparison of the lumi e-gas rates gives a factor of 4.5 higher pressure at the IP w.r.t. 2000, without taking the different currents into account and assuming the same gas composition. For a positron current of 25mA, average current in 2000, the ratio is 8.
Proton background spikes cause severe CJC HV trips, including trips of the cathode wires. This is potentially dangerous. Previously, broken wires were correlated to cathode trips.
Parasitic and dedicated background studies are continuing.
Installation of a residual gas analyzer at NR3.6 before the Christmas break was proposed.
There is no delay of the preparation for the shutdown (VFPS and CIP electronics).

Since Oct. 30 the delivered luminosity is 1.0pb-1. 0.54pb-1 has been collected on tape. The efficiency has to be improved. All detector components are working properly. Too much time is lost at the beginning of a fill. Background rates are now being sent to HERA for a fast background tuning.
The acceptance of the luminosity detector is being studied. The shadow of a collimator is observed. Acceptance/tilt studies have to be done with positron beam.
The main concern is the background in the CTD. After reducing the HV to 95%, a factor of 2 in gain, tolerable backgrounds can be achieved for currents less than Ie x Ip approx 25 x 30mA**2. The ratio of measured to predicted CTD current has recently increased slightly. HV due to background spikes are a problem.
The radiation monitor of the MVD has now accumulated a dose of 90kRad. An increase is now observed at normal running, about 5kRad last week. Radiation damage of the detector will occur at 300kRad.

The detector is in perfect shape. There are no problems during data taking. The detector was usually turned on at 20mA. Recently, after increasing the positron current the data taking started at a current of 24mA. Tuning of the background conditions and luminosity for H1 and ZEUS usually takes a long time.
In total, 330000 DIS events have been collected. Assuming the rate the goal of 1.4 10**6 events would be achieved 2.03.2003. An average current of at least 22mA is required.
Two positron fills (one shift) are needed before Christmas to study depolarizing resonances in the target.

The running statistics is not yet as expected. The target has only been in beam position for 30% of the time. With a data taking efficiency of 74%, the total DAQ time is 5.2 h/day. Most of the time is lost due to operation of the electron machine. 3.5 10**6 events have been taken so far. The number of J/Psi evetns on tape is 70000. Minimum bias data can be logged with a rate of 1kHz.
The most recent problem is beam instabilities and background spikes, which trip the chamber HV. There is no correlation with the target material. Some correlation with the position of the horizontal and vertical wires is seen, mainly vertical wire position.
The target efficiency is less than in 2000. Wires have to be moved closer to the beam resulting in a reduction of the beam lifetime. The proton collimator positions have to be re-optimized.
Additional running time is needed to collect the expected data sample.

Continue HERA luminosity operation as decided in the last coordination meeting with increasing positron intensity.
The date of the installation of the RGA (and cryo pump) at H1 before the Christmas break will be decided in the HERA meeting next Tuesday.
H1 is the coordinating experiment.

The date of the next coordination meeting is Tuesday, 17.12.2002 11:00hrs

Uwe Schneekloth