hera_minutes_050621.html

F.Willeke summarized HERA operation of last week (transparencies to be added)

The efficiency was excellent last week, 69% of the time was spent on luminosity operation. The beam currents are still low. The proton current was limited by problems in PETRA. Good PETRA fills had to be selected. Experts are trying to improve the situation. The maximum electron was 40mA.
HERA delivered about 6pb-1 measured by H1, about 5% less at ZEUS.
Since Thursday electron tunes were lowered at the beginning of a fill. Polarization of colliding bunches increased to 40-45%. The luminosity averaged polarization was 35%. Compared to operation with standard tunes the luminosity loss is about 20% for H1, and somewhat higher for ZEUS. The reduced luminosity at ZEUS is due to the setup of the files. Yesterday evening similar luminosities were achieved in the both IPs.
There were no major technical problems. The increase of the pump reading SR11 yesterday afternoon was due to a water leak. It was repaired during the access this morning.

M.Vogt presented preliminary results of the polarization studies, see transparencies ( 1, 2)

Several tunes scans were performed. Results of the vertical betatron frequency scan were shown. The Lsp values in the plots are not corrected for the decrease as a function of time. The 3 points at fy=12 in the 2nd figure show the specific luminosity at the beginning and end of the scan with and without coupling compensation for the end scan point.
Optimization is still in progress. The main knobs are electron tunes and coupling of the transverse planes.

A.Meyer summarized the H1 status transparencies ( HV eff , bgrd rate, Lsp, Pol )

The present HV efficiency is significantly better than before (up to 90%). The HV can be switched on immediately. The normalized fast rack trigger rate is close to 1.
With mirror tunes the average specific luminosity is 1.40 compared to 1.64 10^30 cm-2 s-1 mA-2. It would be nice if an average polarization of 35% could be achieved with standard tunes.
The access this morning was used for work an the luminosity monitor. The stepping motor was not working properly, moving the calorimeter to a wrong position. The motor was removed. The detector is now in the beam position. Beam losses due to poor injection should be avoided.

A defective FCAL module was repaired during the emergency access yesterday evening. Thanks to the other experiments and HERA. Improvements of the FCAL cabling are planned for the winter shutdown.
The difference in luminosity at H1 and ZEUS is worrying.
The structure in the proton background was observed. The increased background did not caused HV trips.
As pointed out by M.Bieler the general rule is that the HV of all experiment should be off at the end of the 15min countdown. Instructions for the ZEUS shiftcrew will be updated.

Continue luminosity operation with mirror tunes. Increase electron beam current above 40mA. The proton current will be increased to full bunch current when the PETRA problems are solved.
Try to achieve large polarization at high bunch currents without significant luminosity reduction.

HERMES is the coordinating experiment.

Uwe Schneekloth