Minutes of HERA/Experiment Coordination Meeting  02.12.2003

Agenda

• Brief status reports
• Operation until Christmas
  • Beam current limitations
• - Christmas break
• - Operation in 2004
  • Monthly access: first Thursday of month, 1.01. --> 8.01.2004
• Preliminary shutdown dates
• Date of next meeting
• AoB

Minutes:

F.Willeke: HERA Status

• HERA has been delivering luminosity. All procedures are working well. The operation efficiency in November was low (40%) mainly due to the down-time caused by the proton beam loss 04.11.2003. November 20 to 30 the efficiency was 52%. Some remaining technical problems are trips of the 208 MHz proton RF system, alarms of the super-conducting cavities (not yet properly adjusted), false temperature alarms and failures of power supplies. The specific luminosity, typically 1.5 10*30 cm-2 s-1 mA-2, is slightly below the design value, in spite of the low beam currents. The main reason is the large positron emittance. The emittance will be improved by correcting the dispersion.
• The increase of positron polarization was slow. About 50% has been achieved so far. The dispersion has to be corrected for further optimization, which requires some dedicated time.
• The positron intensity is presently limited to about 25mA because of high temperatures at the proton beam pipe at absorber 4 (SR11). The temperature limit was increased to 150deg C. There is no heating at the similar beam pipe NR11. A small misalignment (rotation) of the absorber could be the reason for the heating. The absorber position and the angle of the proton beam pipe will be measured during the access on Thursday.
  The proposal is to finish one of the new absorber with shielding but without coating as soon as possible. Once the absorber is ready, increase the positron intensity without temperature limit. In case there is a leak the new absorber will be installed. If a leak occurs before the absorber is ready, try to realign the absorber if misaligned.
  High temperatures are also observed at the ring outside of the electron beam pipe SR19. The heating usually occurs at the beginning a fill. It can be avoided by beam steering.
• The proton beam intensity is presently limited to 20mA in order to avoid high radiation in case of accidental beam losses after a trip of a low beta quadrupole magnet power supply. Parts of the HERA halls will be controlled areas. Several measures are planned to reduced the probability for an uncontrolled proton beam loss: improved reliability of power supplies, use internal power supply alarms to trigger beam abort, delay power supply alarms, detector current change at power supply, use BPM alarms. In addition, decreasing integration time of loss monitors, installation of fast loss monitors and detection of beam current losses is being considered. The BPM alarm was already tested. It works, although very tight thresholds have to be set. The time schedule for these modifications are: reliability of power supplies 2 months, internal alarms January, BPM alarm next week, fast monitor of power supply current January.
  The neutron dose of yesterday's 20mA proton beam loss was low (maximum 0.25mSv)

• Start-up 29.12.2003. Luminosity running after a few days.
• Preliminary schedule:
  • Luminosity operation until 16.08.2004
  • Shutdown: 16.08.2004 - 08.10.2004
  • Start-up and machine studies: 08.10.2004 - 23.10.2004
  • Luminosity operation: 23.10.2004 - 15.12.2004
  • Machine studies: 15.12.2004 - 23.12.2004
• The length of the shutdown is determined by the interlock tests and repair of BU magnet coils. There is not yet a detailed schedule for the BU magnets. A possible removal of HERA B is not included in the schedule.

W.Zeuner: ZEUS Status

• The detector is in good shape. The data taking efficiency is about 50%; delivered luminosity since 12.10.2003 5pb-1, on tape (HV on) 2.5pb-1. Positron injection is very clean. Some dose has been acculumated by positron beam losses. This should be improved.
• Background conditions have improved significantly. ZEUS will be able to run at full beam currents provided the extrapolations are correct. A new background display is available in the HERA control room.
• Remaining problems are the high temperatures observed at SR11, should try to find a solution without reducing the proton aperture, and save and fast proton beam dumps.
• After the access on Thursday, the detector should stay open until early Friday morning.
• There are no major activities planned for the August 2004 shutdown. The shutdown should be as short as possible.

D.Pitzl: H1 Status , Fig.1 , Fig.2 , Fig.3 , Fig.4 , Fig.5 , Fig.6 , Fig.7

• H1 has been taking data efficiently; DAQ efficiency 87%. The delivered integrated luminosity is 5.8pb-1, on tape 4.7pb-1, HV on 1.8pb-1. It took 3 weeks to recover from the flange leak NL11 on 4.11.2003. The pressure is high at NR8.3 and 10.8. A leak search will be performed on Thursday. The positron beam background was improved last night by flat orbit steering, best conditions achieved so far. For the period 08.10. to 13.11.2003 a neutron dose of up to 2mSv was measured in the hall, 0.8mSv in the control room. Since 1.12.2003 the experimental hall and rooms in the 3 lower floors are controlled areas.
• A beam angle scan is required for the luminosity monitor acceptance. The VFPS at NL220 will continue commissioning after repair of trigger electronics on 4.12.2003. Separation of synchrotron radiation, e and p-gas background contributions requires one isolated positron bunch: 12 empty bunches before, 8 after, in both beams.
• Chamber operation should be possible Ie * Ip = 30*40mA**2 or slightly higher. Beam currents should be increased slowly as background conditions and safety allow. The proton currents should only be increased when the improved failure detection system is in place. Background conditions must be reduced by a factor of 3 for safe chamber operation at design currents. The orientation of the spin rotators should be changed to left-handed e+ after collecting 5pb-1 with 40% polarization. After the Christmas break H1 will be active again on 29.12.2003.
• No major activities are planned for the August shutdown. Work on the Roman pots NL will require breaking the vacuum system in the warm section. The vertex detector, 1/4 of the Si is off, will not be repaired.

P.Di Nezza: HERMES Status

• The detector has been taking data and is in good shape. About 300000 transversely polarized DIS events on H are on tape. Polarization looks promising after the latest HERA tuning efforts (maximum 48%).
• The spectrometer is fully operative. The transverse target polarization is stable at 85%. A new procedure is in place to ramp up the target magnet after positron beam acceleration, before background tuning. The silicon detector (Lambda-wheel) is included in the DAQ. There is a new trigger for DIS and photoproduction pentaquark signatures. Background conditions are good, except that the rates in the top half are a factor of 2.3 worse than in the bottom half.
• Systematic studies of the longitudinal polarimeter are continuing.
• Christmas break: shifts will stop 22.12.2003 24:00hrs and start again 02.01.2004 08:00.
• High density end of fill running is planned starting at a positron current of 10mA.

Polarimeters

• The ratio of the polarimeter measurements was LPOL/TPOL = 1.07. It depends on the fill and is still being studies.
• The LPOL cavity laser broke 2 months ago. It was repaired and is ready for installation. Additional shielding is not yet ready. An access was requested before the Christmas break.

Schedule

• Continue luminosity operation with 120 bunches until at 29.12.2003. Intensity of positron beam is limited by temperature at SR11 until new absorber is ready. Proton current is presently limited to 20mA.
• Access 04.12.2003: Measure position of absorbers N/SR11. GO/GG magnets will not be warmed up. Orientation of spin rotators will not be changed. Start of beam operation 22:00hrs.
• HERMES will do high density end of fills run starting at Ie=10mA, length one hour.
• No scheduled access for installation of LPOL cavity laser and shielding. Access 23.12.2003 07:00 to 15:00hrs is possible.

• This week ZEUS is the coordinating experiment.

• Continue HERA operation 29.12.2003, luminosity operation after a few days of startup.
• Monthly maintenance days: in general first Thursday of every month, except 1.01 -> 8.01.2004
• Preliminary shutdown dates: 16.08. - 8.10.2004

Date of next meeting

Uwe Schneekloth