Minutes of HERA Meeting      09.12.2003

HERA

• Last Tuesday the positron background at H1 was improved substantially by orbit steering.
• Activities during the maintenance day on Thursday:
  • A leak was found at the absorber 4 (NR11) electron beam pipe flange. The pressure decreased after the seal was sealed. The dynamic pressure behavior is now observed.
  • Absorbers 4 were surveyed at the North and South IRs. The S absorber has a 0.5mm offset towards ring inside. It is not rotated. The proton beam pipe has a 2mrad tilt towards ring outside. This would explain the high temperatures on the inside due to synchrotron radiation. The survey of the N absorber showed a large rotation towards ring outside. If correct this would also result in synchrotron radiation hitting the inside. The tilt of the proton beam pipe was however not measured.
  • The electron beam pipe at SR19 was moved to the ring outside, the upstream collimator to the ring inside in order to reduce the synchrotron radiation flux on the beam pipe. At SR19 the temperatures are now 10 - 20% lower than before the movement.
  • The reliability of the low beta magnet power supplies was improved.
  • The voltage of the electron injection kickers was increased. Injection is now more efficient.
• The startup after the access was more difficult than usual. Some machine studies were performed: stabilization of the proton orbit, correction of the positron dispersion. The design emittance was achieved.
• The proton beam dump is now faster. The delay time was reduced from 600 micro s to a few 10 micro s.
• HERA delivered several luminosity fills over the weekend, interrupted by a few technical problems. The temperature at the proton beam pipe SR19 is now slightly higher than before, possibly due to a different position of the temperature sensor. The temperature limit was increased to 185deg C allowing a maximum positron current of about 30mA. For the last two fills good background conditions were achieved without any special tuning.
• Polarization was in the upper forties without any dedicated optimization.

ZEUS

• The synchrotron radiation background was high from Saturday evening to Sunday midday. This was caused by beam steering trying to avoid high temperatures at SR11 as it was not possible to change the temperature limit during the weekend. Data taking was not possible during this period.
• Backgrounds were low for the last 2 fills. The last fill was excellent.
• A significant increase of the positron particle background was observed during the HERMES high density running, see figure. This does not cause any problem at low beam currents.

H1

• In general, very smooth data taking. HERA delivered 640nb-1, 573nb-1 was collected on tape. The DAQ efficiency is 89%.
• The chamber currents improved after the leak NR11 was fixed last Thursday. The scaled CJC2 current was as low as the lowest point last year, see figure.

HERMES

• There were quite some problems. Wednesday a vacuum pump broke in the target region. It was repaired during the access on Thursday. The electronics and trigger suffered from a power failure. The spectrometer magnet cooling water went off. Since Sunday there was a problem related to the low voltage and thresholds of trackers. It was fixed yesterday.
• The first high density run was performed yesterday (hydrogen target). Data were taken successfully. The positron lifetime decreased from 16 to 3.5 hours. High density running should now be done regularly at the end of each fill (Ie=10mA). The target will be Deuterium and Krypton. The beam lifetime will be 2 to 3 hours.

Schedule

• Continue luminosity operation until Thursday late shift. HERMES will do high density running at the end of each fill. The HERA 15min end of fill count-down should start 45 minutes after the beginning of the high density run.
• At the end of this fill the dispersion correction will be tested under luminosity conditions before the HERMES high density run. The H1 and ZEUS HV should be off during this test (about 1/2h). After the high density run the positron emittance will be measured.
• Machine shifts will be performed for one week starting Thursday late shift.
• Monday: 6h access for work on proton magnet power supplies and access for the LPOL cavity laser. The access will be shifted to Tuesday if the electronics card for the power supply is not ready.
• After machine studies luminosity operation will continue until 23.12.2003 7:00hrs. During this period background tuning for HERMES will be done before optimizing for H1 and ZEUS.

                Uwe Schneekloth