COORminutes050830

Minutes of HERA/Experiments Coordination Meeting 30.08.2005

Accelerator performance July/August

The beam currents have not increased. The proton current is slightly reduced due to problems with PETRA. There has been no progress increasing the electron current due to recovery from technical problems, dust and other lifetime problems, background conditions and injection tuning problems. It seems hard to get beyond 40mA.
The peak luminosities, 3 - 4 10^31 cm-2 s-1, are slightly less than in May (maximum 5.1 10^31). The specific luminosity continues to be large, unless the machine is not properly tuned. Luminosity production in August was fine, about 25pb-1 were delivered, but the data taking efficiency was poor due to worse background conditions. There are no indications that the recent poor background conditions were due to technical problems.

Polarization

Polarization is in good shape, i.e. about 30% at the start of a luminosity run, approaching 45% towards the end. The non-colliding bunches have up to 60% polarization.
The rotator settings for the different positions were checked. The sensitivity to the settings is larger than expected.

Short term plans

The maintenance day Wednesday next week will be from 6:00 to 22:00hrs. The tunnel will be closed at 14:00hrs.
It was decided to warmup the GO/GG magnets in the north IR in order to regenerate the NEG pumps. GO/GG will stay cold in the south.
HERA will resume operation with one day of machine shifts to explore the beam stability.
The rotator position will be changed. Polarization has to be retuned again.

Shutdown planning

The shutdown dates are 14.11.2005 to 6.02.2006 (restart of beam operation). Luminosity operation is scheduled to start in the third week of February.
The major shutdown activities are: replacement of BU coils, re-installation of the cryostat #1 with superconducting cavities, a new proton multi-bunch feedback system, and maintenance work.
The BU coil delivery is slightly ahead of schedule. 21 coils are here. The last 4 coils will arrive in October.
The superconducting cavities will be cold-tested in the PETRA hall NE prior to installation, which is scheduled for 12.12.05.

Both polarimeters have been operating very smoothly. The efficiencies are: TPOL 98.2%, LPOL 96.9%, both 99.8%. The measured peak polarization was up to 50%. There were no significant hardware problems. The period of low LPOL luminosity (2 weeks in July) was fixed.
The main problem is a significant shift of the LPOL/TPOL ratio (0.9 to 0.95) in the last few weeks. Both measurements have been checked. There is no obvious problem.
The LPOL cavity performs well, but is still far from routine operation. First Comptons were observed some time ago. Presently, work is in progress to understand the laser polarization.
The new calorimeter was built, checked in the DESY test beam and installed in June. Commissioning is in progress. First data were taken in the HERA tunnel (not yet Compton events). The timing still has to be optimized. A list of task exists, but no detailed schedule. The group is trying to get additional manpower.

Operation

H1 has now collected 76pb-1 with HV on. The average efficiency is 59%. The e- p data sample is now 5 times as large as the HERA I electron sample.
The specific luminosity is usual quite high. It has increased again in recent fills, sometimes as high as 2.2 10^30 cm-2 s-1 mA-2.
The average polarization did not decreased after HERA switched back from mirror to standard tunes.
Last week the integrated luminosity was relative low with poor background. The conditions were much better on the weekend.
The HV efficiency is between 70 and 90%. Last week it was lower due to the poor electron lifetime. The normalized proton background (fast track trigger rate) has increased slightly. The NEG pumps should be regenerated during the maintenance day next week.
Stability of machine operation is a major concern. A significant increase of luminosity is essential for the H1 physics program.

Silicon repair

The silicon detectors and hybrids will be reused for the BST, equipped with radiation hard chips. All modules are ready. Mounting is in progress.
Everything is new for the FST, except the mechanics. Module assembly is almost completed (90% done).
The work is on schedule and will be ready for installation during the shutdown.

Detector operation

The detector is running fine. The gated luminosity is 102pb-1 out of 139pb-1 delivered.
Recently, the efficiency was low due to background problems. Low proton (less than 50hrs) and electron lifetimes (less than 5hrs) cause severe problems. The situation has significantly improved since Saturday. On Sunday ZEUS recorded 1.3 pb-1.
Occasionally high trigger rates dead-time are observed with reasonable proton lifetime. Background tuning is essential, in particular the collimator positions.
The change of helicity next week is supported.

Shutdown planning

The preparations for the shutdown are on schedule. There was some delay of the main carrier of the STT installation jig due to other work in the mechanical workshop. This is not a problem.
The cooling system for the frustum is under construction.
Preparation for some other repairs are in progress.

Data taking

HERMES has collected about polarized 3.8 Mio DIS events 2005. The efficiency is similar to 1997, but still worse than in 2000. The detector is in good shape.
About 9 Mio unpolarized events have been taken. Last month the gas was changed from Xe to Kr.
The cooling problems were solved. An independent cooling system is not required anymore.
The beam polarization is still low. The helicity asymmetry is opposite compared to 2004. The helicity should be changed next week. Another change of polarity might be requested in October.

Recoil detector and shutdown

The recoil detector test experiment is running and taking cosmics. The data is used to determine the efficiency of the different components. The DAQ is ready for integration into HERMES.
Dismantling of the test experiment will start 5.09.2005 in order to prepare for installation.
The shutdown schedule is tight. The main activity will be the installation of the recoil detector. In addition, HERMES has to be moved to the service position for the replacement of BU coils. Some task like survey are already been done at the regular maintenance days.

Uwe Schneekloth