Minutes of HERA Meeting
07.12.2004
HERA
F.Willeke summarized HERA operation of last week.
- Last Thursday the H1 detector was moved by 7mm horizontally (towards ring
outside) in order to realign the GO magnet. In addition the GO tip
was moved up 1.5mm. The GO/GG currents are now close to the design
values. The available aperture is larger than before the realignment.
- First electron proton collisions were obtained on the weekend without
problems. The conditions look rather promising. The specific luminosity
was quite high (maximum 2.2 10**30 cm**-2 s**-1 mA**-2). The proton
bunch length is slightly shorter at the reduced beam currents.
- Background conditions at ZEUS are under control. Background rates at
H1 are very large due to the poor vacuum conditions. With electron
beam the pressure at the north IP is several 10**-8 mbar.
Without beam a pressure bump is observed at NR6 (10**-8 mbar). It has
not improved. A small leak at the GI vacuum chamber was detected
during the last access. Repair is planned for tomorrow.
- It is not planned to regenerated the NEG pumps in the north and south
interaction regions tomorrow. The next regeneration including warmup
of the
GO and GG magnets is planned for 23.12. with cool-down on 27.12.2004.
- So far there was no indications for reduced electron lifetime.
In 1999 lifetime problem only occurred at currents above 30mA.
Congratulations to the HERA crew for the successful start of electron proton
luminosity operation.
ZEUS
A.Geiser summarized the ZEUS status transparencies .
- ZEUS was able to turn on quickly after some brief initial background
tuning.
The conditions were quite good, similar to the e+ p conditions
last May. Data was successfully taken with all components with about
90% data taking efficiency.
- There was a major radiation incident Saturday evening. After the
electron beam was dumped by the radiation alarm the
proton background continued to be very
high for several minutes. A total dose of 5krad was collected
by the radiation monitor, about 10% of the integrated dose since
October 2003. High proton backgrounds are potentially very
dangerous and can cause severe radiation damage.
F.Willeke remarked that some margin is needed when the machine
is setup for luminosity operation.
There will be a separate meeting to discuss when the proton beam
should be dumped in case of high background.
H1
D.Pitzl summarized the H1 status
- Moving the detector on Wednesday was delayed due to problems with a
step motor. On Thursday the detector was moved by 7mm. This was
the maximum. In the closed position the yoke is now touching the
magnet bridge. In principle, the GO tip could still be moved by
another mm if necessary.
- A scalar factor in the luminosity determination was changed by 20%.
The luminosity at H1 is now similar to ZEUS.
- The background is still a factor of 5 worse compared to the conditions
after the leak in July (history plot) .
The CJC2 current limit was reached at a proton gated BToF rate
of 50kHz (plot) .
Now the slope of the background rate versus product of beam currents
is significantly steeper than in July
(plot) .
The HV was turned on briefly on Monday. The current was consistent
with the extrapolation from the BToF rate.
The vacuum pressure (plot) is still
significantly worse than 3 weeks after the leak in July
(plot) .
HERMES
- HERMES did not take data due to problems with the DAQ system, which
will be fixed today. Background conditions seem to be fine, although
the TRD was not yet in operation.
- The target dissociator tube broke. It will be exchange tomorrow.
Schedule
Assuming no surprises with the vacuum system north right.
- Maintenance day tomorrow: stop beam operation 05:30hrs, access until
23:00hrs (all interlocks set). Access to the tunnel north and south
until 12:00, east and west until 17:00hrs.
- Thursday continue with luminosity operation with 60 bunches.
Note added on Wednesday, 8.12.. Repair of the leak in the GI NR7 vacuum
chamber requires venting of the vacuum system and opening of the GI
magnet. No beam operation is expected until Saturday.
ZEUS is the coordinating experiment.
Uwe Schneekloth