HERA delivered about 1.3pb-1 in 5 luminosity fills last week.
The new lumi procedure is working well. Maximum luminosities of
about 3 10**31 cm-2 s-1 were achieved at ZEUS and H1.
The positron background at ZEUS was improved by retracting the
collimator SL15 by a few mm.
There was no significant progress on the coasting proton beam. Jumps
of the proton bunch marker occurred several times. The phase loop cannot
be used. Experts are still trying to find the reason for the
coasting beam.
The horizontal position of the electron vacuum chamber SR19 was changed
during the maintenance day, in order to prevent stress on the electron
flange at SR11 and which was probably the reason for the recent leaks.
Closing the ZEUS calorimeter (fast movement) at injection energy was
tested during the machine studies. Acceleration with closed calorimeter
did not cause any problems. The calorimeter is now closed routinely
after positron injection is finished.
New positron files were established for the new rotator settings.
A new file for slightly lower energy is still needed in order to
perform energy scans.
Beam based alignment was tested in the arcs. The hardware needs
to be improved.
The beta beat of the positron optics was reduced from 30% to 10%.
Luminosity operation resumed Friday late evening. Operation was
interrupted Saturday to Sunday night by a failure of the HERA B interlock
system. The vacuum pressure went up. In total 16 hours were lost.
A power failure (outside of DESY) happened yesterday morning. It took
9 hours to recover.
A polarity switch of a power supply failed last night. The positron
orbit (40mA at 24GeV) was displaced by about 2mm, causing again a
leak (pressure up to 3 10**7 mbar) at the absorber 4 electron flange.
The leak was sealed using vacseal.
The horizontal wire for the proton emittance measurement is broken.
The proton tune is still somewhat unstable. Magnet power supplies
are being checked for noise.
HERA is now back in operation with reasonable background conditions.
A worry is still the reliability of the whole system. The operating
efficiency is presently about 40%.
After the change of the rotators the polarization is about 10%.
The beam energy is about 20 MeV too low. An energy scan will be performed.
Work on beam based alignment and on the depolarizer is in progress.
Last week the delivered luminosity was 1.28pb-1, 0.73pb-1 on tape with
HV on. Since Friday an offline correction factor of 1.09 has been applied
to the online luminosity.
Work on the VFPS and FPS was done during the maintenance day.
One VFPS station is now fully operational.
On Saturday the CJC current was 25-30% on Sunday 15% higher than expected.
Spikes in the positron background were observed at the beginning of the
fills.
The pressure at the IP increased (2 10**-7 mbar at NR3.6), when the
ZEUS calorimeter is closed at injection energy, resulting
in high proton background. It would be better to
close the calorimeter at higher energy (24 GeV).
ZEUS
Data taking was not efficient due to high backgrounds. The
positron background is much better since the maintenance day. Although
the baseline proton background is fine, there are many background spikes
causing CTD HV trips.
The new calorimeter closing procedure at injection energy is working fine.
Other options are to close at 24GeV or before positron injection.
The positron injection efficiency has to be optimized before the full
beam is injected.
The calorimeter calibration had to be repeated several times after the
access. The electronics needs some time to get stable after being turned
on again. After the next maintenance a calibration should also be
done between the machine studies and beginning of luminosity operation.
HERMES
Data taking was not efficient. The positron background, synchrotron
radiation in the TRDs, was high at the beginning of the fills. HERA
should start optimizing using the vertical upstream beam bumps.
There was a communication problem between the HERMES and HERA control
rooms.
A lot of work was done during the maintenance day. The front drift chamber
had sagged, pushing down the beam pipe by 3mm. The drift chamber was
moved up again. The support was improved. The beam pipe is again in
the correct position.
The target polarization measurement is presently suffering from noise
(grounding problem).
At the polarimeter the vertical beam size is much smaller than before.
The ratio of TPOL/LPOL polarization is now close to one.
During proton injection the background is intolerably high (1-2 MHz).
This should be improved.
Schedule
Continue luminosity operation with positron current of about 40mA.
Try closing ZEUS calorimeter at 24GeV and before positron injection.