The vacuum in the south IR recovered very quickly after the repair of
the leak SR11 before easter. Unfortunately, on Thursday another leak
occurred at the absorber SR11. A feed-through of a TSP was damaged. The
pressure went up to 10**-4 to 10**-3 mbar. It was decided to vent the
IR with nitrogen to replace the defective feed-through.
The pressure recovered very fast. Positron beam operation started
again early Saturday morning. The first luminosity run started Saturday
evening.
The reason for the leak was poor electrical connection of one of the
connectors of the TSP due to a mistake during
assembly. All TSPs from 10 to 60m from the IP were checked in the north
and south.
A ground fault in the main proton circuit happened on Sunday. It could
not be localized. Luminosity operation resumed Sunday afternoon after
the ground fault had disappeared. The short happened again yesterday
during proton magnet cycling. It was finally traced to one of the
BU magnets east left. It disappeared after applying 1kV to ground.
The ground fault is not a permanent short, only lasting for 1 - 2 sec.
It could be the cause for some of the proton spikes.
The frequency generator for the accelerators is not in good shape.
The instabilities could be the major source for coasting beam and
background spikes. More diagnostics was installed. The frequency generator
electronics is presently rebuilt.
Proton collimator positions were readjusted. The collimator WR33 (outside)
is used to reduced the coasting beam.
Polarization was between 40 and 50%. It is presently being studied
why polarization is higher at this rotator setting. The only significant
difference is the correction which is applied for the H1 solenoid.
Study of the time structure of the proton spikes would be very useful.
The vacuum recovered very quickly after the recent leaks. The pressures
at the IP and at SR11 are about a factor of 2 and 10 worse than before
the venting. The chamber background is about 30% higher compared to
the last fill before easter.
The main problem is spikes in the proton background causing very
frequent CTD HV trips and low data taking efficiency. High dose
was observed in the MVD when the proton beam was scraped, affecting the
performance of the MVD.
The time structure of the proton spikes is being investigated.
H1
In general, successful data taking. High background was observed during
the positron ramp and setting of positron luminosity optics. The rate
went up to 1MHz. This has to be improved.
(The ramp file is not in a good state. Will be improved.)
HERMES
The detector could be turned on very fast. The high polarization is
appreciated.
The positron only fill on Saturday and of the fill on Sunday was
lost due to electronics problems.
Polarimeter
The LPOL cavity laser and lead shielding for the electronics is ready
to be installed. The time estimate is 2 days. (The next maintenance day
should not be extended to 2 days.)
Schedule
Try to continue luminosity operation with the present problems. Interrupt
if necessary for repairs.
Keep increasing positron current to 45mA. TSPs will be activated before
going to high positron current. The positron injection efficiency
will be improved.