B.Holzer summarized HERA operation of last week,
see transparency .
HERA delivered 7 luminosity fills with varying background conditions.
HERA operation suffered from 5 severe problems:
Until Wednesday there were 5 power glitches. It took 1 to 2 shifts to
recover.
The power company, HEW, was contacted.
The source of some power outages was outside of the Hamburg
electricity net.
Another leak at the absorber SR11 electron flange happened yesterday
morning after a positron beam dump. The pressure increased to 10**-7
mbar. The leak was repaired using vacseal. There is now some
understanding what is causing the leak. Measures will be taken on
Thursday.
Sudden proton beam losses occurred during acceleration. Power supplies
were checked. One was found to be unstable.
Coasting proton beam has been present since Friday afternoon causing
poor background conditions. One fill had up to 15mA coasting beam.
The proton RF system was checked yesterday.
The input of the phase loop shows spikes. Experts are presently
investigating.
ZEUS has suffered from large positron background when the luminosity
file is loaded. The source of the background is not yet understood.
It was improved several times by changing the coupling of the positron
beam. HERA will check whether there is an upstream (SL) aperture
limitation.
The beam separation, displacement of the proton beam, was improved during
the positron ramp.
The proton injection efficiency was improved. The maximum proton
current was 103mA.
Since yesterday both beams are dumped with the ZEUS calorimeter closed.
ZEUS
Background conditions were terrible over the weekend, see
transparencies .
There was only one good fill, late Thursday. Large positron background
occurred when the luminosity file is loaded. It is a factor 3 to 4 higher
than expected. The proton background was clearly correlated with the low
proton lifetime. HERA was not able to reduce the backgrounds.
The positron particle background increased by a factor 5 to 10 during the
HERMES high density runs, compared to only a factor of 2 at H1.
The high density run is only acceptable if the other backgrounds are
manageable.
Both beams are now dumped with the calorimeter closed. Positron
injection with calorimeter closed is also possible. To be tested.
H1
H1 took data with all components. The proton background was high in
the forward muon detector, but still acceptable. Some data had wrong
timing, which was attributed to satellite bunches before and after the
main bunch.
The radiation monitor has not issued any false alarms anymore since
last week.
A slow control computer will be replaced during the maintenance day.
Warnings, e.g. GO/GG cryo alarms, should be ignored.
HERMES
Some background fine tuning was needed at the beginning of the fills.
The proton background was increasing during the runs. Rate increased
from few kHz to 50kHz. The trigger had to be prescaled.
There was some problem starting a high density run at high positron
current. In principle, the density can be varied.
There is a major problem that tracking chambers moved downwards and are
now touching the beam pipe. The chambers will be put back into position
on Thursday. Since this is a very delicate operation, the interaction
region will be vented with dry nitrogen in order to reduce the risk
of damaging the beam pipe.
Guidelines for Dumping both Beams
Always measure proton beam emittance with wire scanner after beams are brought
to collisions, before lumi run is declared.
If proton beam emittance > 30 pi mm mrad, dump both beams.
If proton background too high for all three experiments, measure proton
beam emittance (requires turning off HV).
If proton beam emittance > 30 pi mm mrad, dump both beams.
If proton background too high for one experiment, background acceptable
for other experiments, try to tune background conditions for about 1 hour, including measures which may require turning off HV (e.g. moving proton
collimators).
If not successful, measure proton beam emittance (requires turning off HV).
If proton beam emittance > 30 pi mm mrad and Ie < 20mA,
HERMES high density run for 1 hour.
Dump both beams after HERMES high density run.
If proton beam emittance > 30 pi mm mrad and Ie > 20mA,
dump both beams.
These guidelines should be not used as strict rules. They should help the
experiments to come to an agreement when the beams are dumped.
The final decision whether the beams are dumped will be taken by HERA.
Schedule
Continue luminosity operation.
Maintenance day, Thursday 01.04.2004
Stop beam operation 05:30
If the proton beam is lost during the night shift, HERA will do
some machine studies until 05:30.
Access to tunnel 06:00 - 12:00
Change position of the spin rotators.
The modified power supplies will be tested by MKK in the
afternoon. All measures against uncontrolled proton beam losses
will then be completed.
All interlocks closed, turned on accelerator 22:00
1 shift for startup.
2 shifts machine studies.
Continue luminosity operation Friday late evening.