Minutes of HERA Meeting 05.04.2005

HERA

• Last week operations was rough due to several technical problems.
  • Phasing of the proton 208MHz system (last night shift and Thursday late shift). The proton beam was lost during acceleration. An access is required to repair the system.
  • The 8th electron RF station was used again during the weekend. It started tripping again.
  • The PETRA ground fault was difficult to localize. The power supply was operated without grounding. The short was finally found and repaired on Friday.
• The delivered luminosity was about 5pb-1. The efficiency was about 50%. Usually it took several attempts to fill the machine. Luminosity tuning was difficult in the south after the failure of the photon detector of the ZEUS luminosity monitor.
• Background conditions varied. Some fills were fine, some were really bad.
• A new collimator setting was tried to decrease the number of spikes caused by vertical beam movements. The horizontal primary collimator jaw was moved very close to the beam, the vertical jaws were retracted slightly, in addition the coupling was increased.
• The main culprit for the background spikes is a winding short in one of the BU magnets SR. MKK installed a voltage measurement in the tunnel on Friday. There are no results yet. The electronics seems to be radiation damaged.
  A full set of BU coils for one side of the IP (6 coils) should be available in May.
• The background situation, in particular the suspected BU winding short, was discussed in a separate meeting after the HERA meeting.

ZEUS

• The photon detector of the luminosity monitor started failing on Thursday. It could only be partially repaired on Friday. The hardware expert arrived on the weekend. Experts are trying to repair the system during the present access.
  The spectrometer was used for the luminosity measurement.
• The detector is fine. The number of CTD HV trips is increasing, which is a major concern ( transparency). There is a severe risk for the CTD.
  F.Willeke proposed to improve the communication, e.g. the HV could be turned on immediately after some optimization is finished.

H1

• Last week HERA delivered 5.4pb-1, 4.7pb-1 was written to tape. The average HV efficiency was 30-60%, which is less than in previous weeks.
• The total delivered luminosity is now almost 55pb-1.
• Background spikes are present from the very beginning. Scraping with collimators does usually improve the situation, but not always. The number of CJC HV trips is about 250/week.
• The electron beam was dumped on Saturday as requested by H1.
• The proton beam gas background is now close to the goal.
• The synchrotron radiation background was improved by optimizing the vertical orbit at the BH magnet and collimator adjustment. The tracker currents decreased by 15%.
• The horizontal vertex position changed again by about 0.4mm.
  This was done by the HERA shift crew in order to optimize the background conditions.

HERMES

• The proton background spikes are seen in the veto rate. They are not causing chamber trips. HERMES was usually able to continue data taking during proton beam scraping. Recently, the HV had to be turned off. HERMES would like to be informed before the proton beam is scraped.
• Higher polarization achieved recently is very welcome.
  M.Vogt remarked that this is mainly due to lower tunes. The vertical tune can be decrease at the beginning of a fill. The harmonic content of the orbit is drifting. Tunes can still be optimized.
• The trip rate of the ZEUS CTD increased during some high density runs. The target density can be reduced if necessary.

Schedule

• Fix present problems. Continue luminosity operation.
  The new procedure for setting the proton collimators will be used again.

                Uwe Schneekloth