HERA delivered luminosity for most of last week (transparency ) except two interruptions:
a break for HERMES on Thursday and technical problems on Sunday, when
the septum did not fire correctly due to water interlock problems. The
repair was quite lengthy. In addition a computer was affected by a virus.
Yesterday an RF transmitter had a faulty pump, causing some delay.
Otherwise operation was rather smooth. Luminosity fills were shorter
than before. The HERMES high density runs were started at Ie=20mA.
The main problem is still the large coasting beam production. The RF
system was checked during the break on Thursday. Large 50Hz noise (twice
the synchrotron frequency) was found on the input of the 208MHz system.
One of the temporary synthesizers
is noisy. It is a good candidate for the coasting beam production.
The positron current was increased. The maximum current was 47mA.
Above 40mA 5 to 6mA were always lost. Work is in progress to improve
the electron RF system.
Last night the positron beam was dumped due to a temperature alarm.
The beam orbit was not optimized.
The present positron ramp procedure is to load the luminosity optics
while the beam is accelerated from 24 to 27.5GeV.
Background tuning at the beginning of a luminosity run is now quite
fast. The orbits are very reproducible. Moving in the proton collimators
takes the longest time.
Some time of the machine shifts after the maintenance day will be spent
on improving the positron injection efficiency. In principle, a factor
of 2 improvement is possible.
The intermediate frequency generator will be restored during the
maintenance day on Thursday. The strong production of coasting beam
is expected to disappear, although there might be other sources.
A major overhaul of the frequency generators is planned for the summer
shutdown.
HERMES
HERMES had a really nice week. Data taking was very efficient.
The access for repairing the target last Thursday was acknowledged.
The TRD background continues to be high at the beginning of the fills.
High density runs should not start at positron currents greater
than 20mA.
H1
Last week HERA delivered 3.1pb-1, 1.7pb-1 was written to tape with HV on.
The HV efficiency was somewhat lower than before due to increased
background conditions. Turning on all HV still takes about 20 minutes.
The fills Saturday morning and last night had very good background
conditions. More messages on the HERA screen or entries in the log book
would be useful in case there are delays like last weekend.
The increase of noise in the silicon detector is a concern. It is
correlated with proton beam losses. Presently, 1/3 of the BST pad
detector is inefficient.
ZEUS
ZEUS can usually turn on at the beginning of luminosity operation, see
transparencies . Background conditions
deteriorate as a function of the coasting proton beam, causing many
CTD HV trips. Conditions are not tolerable when the coasting beam is
between 2 and 3mA.
The CTD HV trip threshold was increased by a factor of 2. The integration
time cannot be increased. There was one good fill (Saturday to Sunday).
Data could could be taken although the coasting beam was up to 6mA.
Last night the baseline background was quite good. Beam gas interactions
is not the main background anymore.
Radiation damage has been observed in the luminosity spectrometer.
Since 20.04.2004 HV trips of the spectrometer PMTs have occurred when the
positron beam reaches full energy.
Schedule
Luminosity operation until maintenance day.
Thursday: stop beam operation 06:00hrs, warm up GO/GG magnets.
Access to the tunnel (except east) will be limited to 12:00hrs.
Power supply/magnet tests will be done in the afternoon. Access for
the LPOL will be possible until 23:00hrs.
The intermediate frequency generator will be restored.
Thursday to Friday night: proton machine studies.
Friday: positron injection studies, beam based alignment in the arcs.