F.Willeke summarized HERA operation of last week
( transparencies).
HERA delivered 4.85pb-1 last week. Up to 900nb-1 was delivered in one
fill. The efficiency was still relatively poor (46.3%).
The source of the background spikes is still unclear. Small beam
movement were observed in coincidence with background oscillations.
Power supplies are still being checked.
For the recent fills the proton collimators were individually
moved to the beam. The beam position at the collimators
has not yet been changed to check whether possible damage of the
jaw surface causes any problems.
There are no indications for problems with the RF system.
Friday and Saturday there were 2 fills with 18 additional electron
bunches. The idea was to accelerated the conditioning of the vacuum
system by increasing
the electron current. Since HERA was still suffering from serious
background problems, the machine went back to the
standard bunch pattern Saturday afternoon. The machine parameters
should not be changed as long as there are problems.
Polarization of non-colliding bunches was above 45%. Polarization of
the colliding bunches is reduced by beam-beam effects. It grows
during a fill as the proton beam size increases, reducing the
beam-beam effects.
A test was performed observing polarization after the proton beam was
dumped while keeping the tunes unchanged. Polarization of the non-colliding
bunches decreased. Polarization of the colliding bunches went up.
The electron only fill last night had very high polarization. 54%
was achieved very quickly. It decreased slightly during a
bump scan and didn't recover when the scan was finished.
The quench protection is causing problems since Sunday. The reason
is not yet known. Proton operation was not possible last night.
The maintenance day already started this morning.
ZEUS is taking data. The background conditions are however
not satisfactory (15% loss luminosity due to tuning). The beam
gas background is low. Large spikes are causing CTD HV trips.
All measures are supported to diagnose and improve the background
situation. A plan should be made how to attack the
problems systematically.
The proton background is predominantly observed on the ring outside.
ZEUS is able to run at beam currents of Ie=40mA, Ip=90mA
under the present conditions. The currents should be increased
as soon as possible.
H1
D.Pitzl
The chamber current did not improve since last week, see
plot
of CJC2 currents vs. product of beam currents.
Regeneration of NEG pumps this week should improve the vacuum.
The total delivered luminosity in January was 13.2pb-1
( plot), 4.4pb-1 with CJC2
HV on, only 1.7pb-1 with full HV.
The main problem is proton background spikes. Big spikes
( plot) have a fast rise time and
few minute decay and lead to HV trips.
The CJC HV can survive most of the smaller one or two minute
frequency spikes
( plot,
plot).
The background improved after the collimators were readjusted on
Sunday ( plot).
The HERA crew should continue to monitor power supplies. If one
is suspicious, it should be checked immediately.
HERMES
HERMES is very happy with the running conditions, except
for the low electron current. It should be increased as much
as possible. 34mA was the largest electron current injected so far.
The high polarization of last nights fill was appreciated very much.
The glass dissociator tube will be replaced tomorrow. The work may
not be finished before 15:00hrs.
Schedule
The maintenance already started this morning.
The position of the spin rotators will be changed.
The goal is to restart beam operation in the evening shift tomorrow.
3 shifts will be spent on machine development.
Continue luminosity operation with 120 bunches colliding bunches
after the machine shifts. Increase the electron current up to 35mA.
Discuss increasing number of bunches next week.
Background conditions and measures to be taken will be discussed
tomorrow at 15:00hrs.