hera_minutes_050809.html

F.Willeke summarized HERA operation of last week (transparency)

Luminosity operation was fairly good last week. HERA delivered 6.25 pb-1. Beam currents were Ip 80 - 90mA, Ie 28 - 35mA.
After the break on Thursday machine operation restarted as planned. Proton background conditions were somewhat painful, in particular due to GA spikes. The original power supply had been reconnected on Thursday. The background conditions improved after switching back to the spare power supply Sunday afternoon.
Several technical problems occurred: proton quench protection dump switch, sextupole measurement, coupler window temperature of superconducting cavities, phasing of cavities and proton RF system.
The electron collimator procedure was changed yesterday in order to reduce the background during acceleration.
The superconducting cavity, which was removed a few weeks ago, should be ready in about 2 weeks. Re-installation will take 2 to 3 days. It is not yet clear whether this will be done during the maintenance day in September or whether the maintenance day will be moved forward.

Y.Yamazaki summarized the ZEUS status (transparency)

The barrel calorimeter was successfully repaired during the access on Thursday. (Thanks to HERA and other experiments for the access.)
Proton spikes came back on Saturday causing frequent HV trips. The luminosity loss due to spikes was between 10 and 40%.
Except for the very first part of the fills, the proton background was usually about a factor of 2 higher than the baseline background. The collimator positions should be retuned.

So far HERA has delivered about 125 pb-1 this year. The luminosity on tape with HV on is approaching 70 pb-1. 30 pb-1 have been taken with the present rotator setting. Changing the beam helicity should be discussed next week.
The overall slope of delivered luminosity is similar to the slope in February. The progress is disappointing.
Beam currents are still relatively low. The specific luminosity was quite good, slightly above 2 10**31 cm-2 s-1 mA-2 at the beginning of a fill.
The HV efficiency was up to 90% for good background conditions. Sunday morning before the switch back to the spare GA power supply it was only 40%.
Vacuum conditions have been stable since the beginning of July, the last time the NEG pumps were regenerated. Firing TSP's twice per week keeps the vacuum at a constant level. Improvements have only been observed after NEG regenerations. This should be repeated during the September and October maintenance days.
Last Tuesday the GO magnet was moved 1.5mm ring outwards. The dipole current was reduced.
At NL220 the proton orbit was moved horizontally by 8mm to increase the acceptance of the VFPS. A 7mm orbit bump is now in the file. The pots were moved in 6mm.
The photon spot in the luminosity monitor is still 1.5cm off, introducing an acceptance correction of 10%. The offset should be corrected.
The tilt bump is presently used to correct the dispersion. Alternative bumps are being studied by the machine group.

Good data taking. The background during proton injection improved by a factor of 10 to about 1 MHz. It should be improved further.
A 1 h access is needed to repair a defective chamber.
Since last week the LPOL/TPOL ratio is off by 20%. It is not yet clear why.
Polarization is slightly worse than before, not approaching 50% at the end of a fill.

As always, aim for increasing luminosity, low background conditions and high polarization.
The change of helicity will be discussed in the meeting next week.

HERMES is the coordinating experiment.

Uwe Schneekloth