Luminosity operation was stopped last Wednesday for machine studies
before the access.
Activities on the maintenance day included warm-up of GO/GG magnets,
regeneration
of NEG pumps and installation of quadrupole magnet power supply alarms
in the South IR.
A cavity window in the NL RF section broke on Friday, venting the vacuum
section. The cause of the damage is not understood. Windows are replaced
during shutdowns if necessary.
Machine studies, trying to understand the low specific luminosity, were
performed after the repair of the RF window.
The results of the beam scans will be discussed on Thursday.
Luminosity operation was resumed on Sunday without any problems with
somewhat reduced beam currents and lower positron lifetime due to the
poor vacuum in the RF section. The positron current has been increased
slowly (yesterday 25mA).
The newly installed power supply monitor gave a few false alarms,
aborting the proton beam. It has to be checked out.
The so called Horn ACCT beam current monitor, delivering the
bunch current through the HIT system, is defective. Since it is
no longer supported it was replaced by the "Neumann" current monitor
on Saturday.
The currents of the Horn monitor were about 6% too high. The
discrepancy between the specific and instantaneous luminosities
is now gone.
Polarization is still low. Longer fills are needed for re-optimization.
The fact that the polarization increased to almost 50% when the H1
solenoid went off 2 week ago is an indication that the spin is not
completely longitudinal at the IP.
H1
The noise of the VFPS was improved during the access. One station is
now operational, the 2nd station not yet. 3 out of 4 FPS stations are
operational. They will now be operated during HERA fills.
Maintenance work was performed on the SPACAL and solenoid.
H1 took data since Sunday. Sunday to Monday night the positron beam
was dumped due to high background.
The latest NEG pump regeneration gave a 30% reduction in the proton
induced background, which translates into a 13% reduction of the total
chamber current at Ie*Ip=55*105 mA**2.
The p-gas background is now slightly less than the SynRad plus
e-gas background, where the latter is expected to decrease again
after recovering from the vacuum leak at the cavity NL78m last Friday.
At high luminosity we were always willing to increase our chamber current
limit from 150 to 200 microA, which allows to run at 50*100 mA**2 now.
The operating voltage of the CJC was increased last Thursday (5.2.),
leading to a 20% gain and current increase, for increased hit efficiency.
This effect was taken out in the plots attached.
At higher beam currents we have the option of reducing the gain again.
ZEUS
The proton background improved significantly after the access,
see presentation. It is
now a factor of 2 below the parameterization of December. Although the
positron background is slightly higher than the parameterization, the
overall background situation is excellent. Chamber operation at design
beam currents is possible.
The pump at the absorber SR11 shows a slow increase of pressure,
consistent with saturation of the TSPs. High pressure is also seen at
the photon vacuum chamber SR25. There might be a small leak.
A leak search should be performed.
High background caused by bad proton tunes was observed. Two positron
beam losses resulted in some increase of the MVD dose.
The power supply of the solenoid was grounded on the access day.
There have been no magnet trips since then.
A request was made to extend the next access to 48 hours. There are
2 reasons: Maintenance of the emergency cooling system, this requires
a period of 6h without any cooling, and repair of the concrete underneath
the rails. The new concrete has to dry for 24h.
HERMES
Service work was done during the access.
The experiment has been running smoothly. Background conditions are
better than in the previous week. A gate valve continues to close
during proton acceleration.
The end of fill running as discussed. Since the positron current
is still lower than before the leak on Friday, the high density run
will not start at Ie=13mA, as decided last week, but at 12mA.
Schedule
Continue luminosity operation with increasing beam currents with 120
bunches. (Increasing the number of bunches will be discussed next week.)
HERMES high density target runs will start at Ie=12mA.