Minutes of HERA Meeting
30.09.2003
HERA
M.Bieler summarized HERA operation of last week.
- Polarization studies were interrupted by
two incidences. A ground fault in the proton ring occurred on Thursday and
venting of the south IR (SL 26 to SR26) Thursday to Friday night.
- The leak occurred at the electron beam pipe flange of absorber 4 at SR11.
New positron files had to be prepared with the proton magnets turned off.
The positron current was 1.5mA. The leak happened only two minutes after
the next positron fill was accelerated to 27.5GeV. The explanation for
the leak is that the electron beam pipe flange of absorber 4 was hit
by direct synchrotron radiation on the ring inside causing the leak.
The closest temperature sensor, located inside absorber 4, was at 64deg C
(34deg C temperature increase) instead of 42deg C (12deg C increase) at
similar beam current.
The pressure at the next turbo pump station was 50mbar when the TP valve
was opened. The flange was tight again after the screws were tightened.
It was however decided to replace the Cu seal by a Nb seal.
(Extensive tests in the workshop had shown that Nb seals are much less
sensitive to asymmetric heating of a conflat flange).
The GO/GG
magnets were warmed up in the morning. The seal was replace in the
afternoon. NEG pumps were activated yesterday. TSP pumps have been
activated several times. GO/GG are being cooled down today.
Additional temperature sensors were installed on Friday.
Analysis of the beam orbits and a simulation of the synchrotron radiation
deposition and heat distribution is in progress. Limits on the beam
position and temperatures will be defined in order to avoid any further
leak due to synchrotron radiation.
-
The proton ring ground fault only occurs after 30min of operation.
By measuring voltage drops and by disconnecting magnets it was traced
to the BU magnets NL. The ground fault did not happen when the proton
dipole was powered without the BU NL magnets. One of the BUs had a
water leak, which was repaired but not causing the ground fault.
Additional diagnosis is now installed to find the defective magnet.
The plan is to move the virtual ground to the BU coil with the ground
short in order to enable operation. This will be finished tomorrow.
(Exchange of a BU magnet would take about 3 weeks).
- The maximum polarization was 40%. The harmonic bump scan was not
completed. Another energy scan is necessary.
- Two quadrupole magnets in the east straight section were re-aligned
during the access (OR11 and OR14 moved up by 1 and 2mm).
- The schedule is delayed by about one week.
Polarimeters
- The commissioning of the polarimeters is not yet finished. One additional
positron fill is needed for the transverse polarimeter.
H1
- The VFPS fiber detectors were installed yesterday. The 40m are 6m
tagger are installed. An access is needed to set the end-switches of the
VFPS. The emergency switch at the VFPS is not yet connected.
ZEUS
- Analysis of the positron runs shows that the reflected synchrotron
radiation background in the CTD has been reduced significantly.
Schedule
- Cool down GO/GG south IP today.
- Repair proton ground fault until tomorrow.
- Continue with beam operation. Try to reproduce conditions of Thursday
(very small current).
- Positron currents depending on vacuum conditions.
- Try to set up luminosity on weekend.
ZEUS is the coordinating experiment.
Uwe Schneekloth