Minutes of HERA Meeting      16.12.2003

HERA

• Early last week HERA delivered several long luminosity fills.
• Machine shifts started Thursday afternoon.
  • The specific luminosity was studied for different beam tunes. Lsp was slightly higher at the injection tune (step 1). The second fill (only few bunches) had very high specific luminosity (2.1 10**30 cm-2 s-1 mA-2) in both tunes, step 1 and step 4. Lsp may depend on the number of bunches, which is not understood.
  • The magnet bridge NL was moved up by 0.6mm with beam to improve the GI position. It worked as expected. There is a good understanding of diagnostic tools and magnet positions.
  • Proton orbit stabilization was tested. It will be implemented in routine operation.
  • The proton beam position offsets were reduced during the ramp and at full energy in order to avoid alarms of the new BPM alarm system. Alarms are set at 3mm orbit displacement.
  • The horizontal and vertical positron dispersion correction was tested for luminosity optics. The emittance decreased by about 10%.
  • Yesterday fast power supply alarms were successfully tested on one low beta quadrupole power supply.
  • The beam current monitor could not be tested with beam due to delayed proton injection
  • Beam based alignment measurements of the interaction regions were done. Results are not yet available.
  • Polarization studies started last night.
• The 8th electron RF station will be ready this week.
• There is not much progress on understanding the heating of the absorber 4 proton beam pipe. The proton vacuum chamber NR11 could not be surveyed yesterday. The maximum positron current is about 30mA.
• Note added after the meeting: The last brazing process of the new absorber 4 with small collimators to protect the downstream vacuum chamber but without coating will start tomorrow. It is expected to be ready for installation middle of January.

• Conclusions:
  • Incident rate of uncontrolled beam losses of protons increased by increased number of critical circuits, new power supplies and limited time allocated for maintenance
  • Reasons for these losses are well understood
  • Efforts are being made to avoid trips of the low beta quadrupole by an aggressive preventive maintenance program
  • Beam losses can be modeled and are in reasonable agreement with measurements.
  • Modeling of losses suggest that uncontrolled beam losses are best avoided by fast alarms of the power supply --> highest priority
  • Signals from beam measurements (BPCs, loss monitors) will provide additional safety in conjunction with the now speeded-up dump and alarm system.
  • Tight collimator settings will help to get early beam loss signals
  • Additional shielding should help to reduce radiation dose in case an event occurs despite all efforts
  • --> Propose to return to high intensity protons by Dec 17
• There were no objections to going back to high proton currents provided the controlled areas are established in the experimental halls (HERMES has not yet received dosimeters) and the measures against beam losses are reviewed in the next HERA coordination meeting 20.01.2004. Concerning the power supply alarms, the GN magnet power supplies will be monitored first. The alarms will be implemented in the alarm loop as soon as they are available.

ZEUS

• Background conditions have improved. Operation of the drift chamber should now be possible at full beam currents (Ip=100mA, Ie=50mA), see figure.
• Neutron dosimeters were received yesterday. This afternoon the experimental hall will be a controlled area.

Polarimeters

• The transverse polarimeter is working properly.
• The LPOL cavity laser was installed yesterday. It is working, although there is a problem with the remote control.

Schedule

• Continue machine studies until Thursday.
• Tomorrow test of safety system. Tomorrow evening go to higher proton current.
• Thursday continue luminosity operation.
• 23.12.2003 07:00hrs end of luminosity operation. Day shift turn off accelerators.
• 29.12.2003 start-up of accelerators.
• Next HERA meeting 30.12.2003

                Uwe Schneekloth