Minutes of HERA Meeting 13.09.2005

HERA

• The maintenance day last Wednesday went as planned. The machine studies were delayed due to problems with the interlock. Luminosity operation resumed Friday to Saturday night.
  The first two fills lasted only a few hours. The specific luminosity was relatively low.
  The third fill was was very quiet, high luminosity and good background conditions.
• Luminosity operation stopped Saturday to Sunday night because of two leaks in the electron vacuum system (rotator section east right and absorber SR11).
  • The leak east right occurred due to overheating of an absorber which protects the vacuum chamber from synchrotron radiation. Up to 5kW of synchrotron radiation is deposited on 3 cm^2. The synchrotron radiation had been overlooked in the original design, causing a leak in 1997. Absorbers were added in the next shutdown. It is not clear why the vacuum chamber got hot. The only explanation is insufficient thermal contact between the absorber and the beam pipe. The water cooling was checked. All other locations were checked as well.
    The vacuum chamber was removed yesterday morning. A spare chamber is presently being prepared. It will be installed tomorrow afternoon.
  • The leak at the electron flange SR occurred after the electron beam loss. The same flange had several leaks before. Last time, in early March, it was fixed by tightening the screws. It was therefore decided to replace the seal. Yesterday the GO/GG magnets were warmed up, the IP was vented. Today the seal was replaced.
    The same procedure will be used for activating NEG pumps as in April 2004, when the vacuum recovered very quickly.
  • The startup schedule will be discussed tomorrow morning.
• The position of the spin rotators was changed during the maintenance day. Polarization was 20% without any tuning. The first bump scan was started.
• The proton beam losses at HERMES during injection were reduced.

ZEUS

• CTD operation was problematic on the weekend. The HV continued to trip after the synchrotron radiation background had been improved although the background was quite low. Trips were also observed without beam.
  The HV system is presently checked by experts.

H1

• The CJC current is now, after regeneration of NEG pumps, below the expectation. The normalized fast track trigger rate improved significantly. It is now 0.7. The vacuum at the IP is similar to the pressure in the south.

HERMES

• Shifts are canceled until Wednesday morning.

Schedule

• Beam operation will not restart before tomorrow evening. The startup schedule will be discussed tomorrow morning.

                Uwe Schneekloth