B.Holzer summarized HERA operation of last week,
see transparency
HERA delivered several luminosity fills last week, except for the
maintenance day on Thursday followed by machine studies and a break
on Saturday. There were a few technical problems: a power supply for
a correction coil failed and was replaced, two ghost quenches and some
cryo problems. Once the positron tune jumped when the tune was
readjusted, causing large background and a beam dump fired by the ZEUS
radiation monitor.
The intermediate frequency generator was repaired and reinstalled on
Thursday. The signal to noise ratio is much better than before.
This
is also seen on the input to the proton RF system. Side lines, which
were visible before, have disappeared. The coasting beam production
is reduced significantly. Some diffusion of protons into the neighboring
buckets is still observed. The proton bunch length is shorter with less
satellite bunches, see transparency .
At the end of the last luminosity fill the coasting beam was 4mA.
Other sources for the coasting beam production are being studied.
Five proton beam position monitors were repaired. This is important
to avoid poor lifetimes and high backgrounds during acceleration and
background tuning.
An electron ring quadrupole magnet (GJ SR8) had a ground fault after the
access. It took several hours on Saturday to remove the shielding in
order to get access to the magnet. A cable was shorting the magnet
current leads.
During the machine shifts the electron transfer line from PETRA to HERA
was retuned. An efficiency of 90% was achieved. There was no time to
optimize injection into HERA.
The positron current was increased to 45mA without vacuum problems. HERA
will continue to increase the current in small steps.
This morning 50% polarization
(transparency )
was obtained by tuning harmonic bumps and beam tunes.
The initial specific luminosities were typically around
1.3 10**30 cm- s-1 mA-2 at the beginning of fills, decaying slowly.
More routine operation is needed to increase the stability.
Magnet current jumps (QP27N current changed by 50 bits) and background
spikes causing HV chamber trips were observed when the main station C
transformer is switched. This happens about 10 times during a luminosity
run. Some power supplies were already readjusted to reduce the
sensitivity to voltage changes.
For the first time the HERA control system was affected by a virus.
For most of the fills the efficiency was very poor due to spiky
background conditions. From Monday to Monday 1.5pb-1 were delivered,
0.6pb-1 written to tape. The conditions improved significantly after the
repair of the frequency generator. Last night conditions were very
good (only
5 HV trips, 0.4pb-1 written to tape) except for the end of the fill
when background conditions deteriorated.
The baseline background is excellent after the regeneration and
activation of pumps during the maintenance day. The proton beam gas
background is a factor of two below the extrapolation from November.
The positron background improved recently and is also below the
extrapolation.
H1
D.Pitzl summarized the H1 status.
In April chamber currents increased by about 30%,
pumps were not regenerated
during the April maintenance. After the warmup of GO/GG and regeneration
and activation of pumps last week the background decreased again,
see transparency .
The dependence of the CJC current as a function of beam currents is
as expected, see transparency .
Last night there were 3 HV trips in the outer, 4 in the inner chamber.
HERMES
Successful data taking. After the access the spare power supply for the
lambda wheel detector broke. The lambda wheels are presently off.
In case of an access, HERMES would like to use the opportunity to
to repair or replace the power supply. There were some DAQ problems
when HERA was down on the weekend.
Huge proton background spikes (MHz rate) were observed during proton
injection, causing trips of the hodoscopes at standby voltage.
The proton orbit will be reoptimized by HERA.
Tried to speed up switching from the atomic beam source to unpolarized
target for the end of fill runs.
The TRD background is still high at the beginning of luminosity
operation.
Polarimeter
B.Zihlmann presented a transparency prepared
by S.Schmitt.
The polarimeter group is ready to switch on the kicker magnet and
scan the frequency until resonances are found.
2-3 hours will be needed to do a rise-time calibration.
It was agreed to do the depolarization studies at the end of luminosity
fills instead of the HERMES high density runs during normal
working hours.
The first test will be done tomorrow.
Schedule
Continue luminosity operation. Increase positron current in small steps.
During day time depolarization studies will be done at the end of
fills (at Ie=20mA for about 2hrs) instead of the 1h HERMES high
density run. The first test will be done tomorrow.
