HERA delivered an integrated luminosity of 3.1 pb-1 until Saturday
morning. The
maximum positron current was 53mA. The beam was however lost due a
RF trip. The positron current had to be reduced to 40mA and was slowly
increased again. Polarization was between 40 and 50%.
A leak occurred at the absorber 4 (NR11) proton flange on Saturday at
5am after the beams were dumped.
The seal (VAT seal) was exchanged after warmup of the GO/GG magnets. The
flange connection was not leak tight after the installation of the
new seal. It had to be replaced again.
HERA resumed beam operation Sunday evening, bake-out with positron beam.
The leak reoccurred yesterday evening. The GO/GG magnets had to be
warmed up again. The seal was removed this morning. It will be examined
today. It was noticed that the flange surfaces are not parallel.
This could be caused by a movement of the proton quadrupole magnet
or the absorber. A survey will be done today.
ZEUS
Data taking was fine. Most worrying is the behavior of the solenoid.
Last week it ramped down 3 times due to high temperatures. After
the beams are dumped, a temperature increase at the superconducting
cable is usually observed in coincidence with an increase of the
heat shield temperature. The reason is not understood. ZEUS is in contact
with Ansaldo and the DESY cryo group. A calorimeter calibration has to be
performed every time the solenoid is ramped up again.
H1
Data taking was fine, except for the second positron fill (on the same
proton fill) Thursday evening. 2.7 out of 3.1pb-1 were written to tape.
Positron refills should be avoided.
HERMES
Data taking was fine, with the exception of high proton and synchrotron
radiation background at the beginning of the fills.
The LPOL calorimeter was removed last week. 3 out of 4 crystals are
severely damaged, most likely due to high temperature.
The calorimeter was reinstalled with new crystals. Temperature sensors
were installed.
Schedule
Continue with beam operation after the repair of the leak and cool-down
of GO/GG.
The plan is to do positron beam bake-out with highest positron
currents at 27.5GeV until the positron current is high enough to
achieve a peak luminosity of 2 10**31 cm-2 s-1.
Change position of spin rotators today. The positron bake-out will be
used to optimize polarization.