Luminosity operation started 11.10.2003. Standard operating procedures
have been established. Typical present beam currents are:
Ie 15-20mA, Ip 50mA in 120 bunches.
The injection efficiencies are acceptable. The specific luminosity
is not yet at the design value. At H1 it is about 20% higher than at
ZEUS.
Polarization is about 30% (without any tuning since September).
Some high temperatures are observed at NR/SR. Background tuning is
still time consuming.
Several problems occurred in September and early October.
The south IP was vented on 26.11.2003 due to a beam induced leak at
absorber 4 (SR11). The reason was found
(synchrotron radiation, caused by large orbit displacements, hitting
a flange). Measurements were taken to prevent any further leaks.
The vacuum at the IP recovered relatively quickly after a few days
of 12GeV beam bake-out.
A ground fault occurred in the BU NL73 magnet (vertical proton
bending magnet). Replacement of the defective coil would take about
4 weeks. In order to continue operation, the grounding scheme was
changed. 9 new BU coils were ordered. The first 3 coils will be
delivered
in March 2004, the last one in August. Replacement of all BU coils
NL is planned for the next shutdown.
Vacuum conditions at the IPs are quite good. Large pressure increases
are no longer observed during positron injection. At a positron current
of 15mA the IP pressure is about 1 nTorr.
The maximum positron current is presently limited to about 30mA because
of RF trips. Cavities are now conditioned between fills.
The RF station which was affected by the fire in June will
be back in operation in December. Another limit might be the temperature
of vacuum chambers and flanges NR/SR.
The presented schedule for 2003 is the same as in July. The only
significant change is that luminosity operation was delayed by 2 weeks.
First look at operation in 2004/2005
Try to minimize 2003 Christmas break. Continue running if possible.
A 5 week break is needed in 2004 for various activities: interlock
tests, exchange of BU NL magnet coils, DESY II main choke, maintenance
and improvements. The break should not be during summer school
vacations.
H1 started data taking with all components. The central inner
proportional chamber is operational including the trigger. One quarter
of the silicon vertex detector is defective. Repair would require a
6 week shutdown (not requested now). The VFPS fiber detector was
installed.
Background conditions have improved significantly.
For the positron
only fill (25.09.2003) the background was better than during the last
running period. Synchrotron radiation background is no longer visible
when the positron beam is tuned properly. This hasn't been achieved
under luminosity conditions. The GO magnet was raised to improve the
beam orbit. The number of hits in the CJC is reduced due to the new
lead shielding.
The CJC current is small for p-only.
During ep operation (Ie=14.5mA, Ip=51mA) the CJC1 current was at 50%
of its limit.
Requests:
The lumi detector needs a position scan (no change of beam orbit)
and a beam tilt scan at 27GeV.
The VFPS detector requires a special p orbit at NL220.
An isolated positron bunch is required to separate background
contributions (12 empty bunches before, 5-8 empty bunches after
isolated bunch for both beams).
Plans:
Beam currents should be increased: Ip x Ie = 60 x 25 mA**2. Achieve
design specific luminosity.
Optimize positron polarization. Change to left-handed after 5pb-1,
pol >= 40%.
Long, stable data taking in 2004. Exceed HERA I integrated luminosity.
All detector components are operational and ready for data taking.
Some recent problems were:
Defective electronics of the solenoid control. This was solved
by swapping units. Spare parts are now available.
A leak at absorber 4 (see presentation by F.Willeke).
A smoke alarm in the electronics trailer due to a defective power
supply of the CTD electronics.
The background conditions have improved significantly.
At present, the synchrotron radiation background is no longer visible
in the CTD. There is no indication for delayed hits due to backscattered
synchrotron radiation. The positron beam gas background is back to
the level before the leak. The proton beam gas background is about
20% less than early this year. At present beam currents, the CTD current
is 1/2 of the maximum chamber current.
Beam currents should be Ip x Ie = 60x 20mA.
There is no need for a shutdown next year.
Note added after the meeting
Ratio of CTD current over expected current vs. day
plot during luminosity operation. The expected
CTD current is derived from a fit to the data of the last running period
including a factor of 10 improvement in synchrotron radiation and a
factor of 2 in e-gas background. Note that there was very limited beam
operation at 27GeV after the venting of the IP and the first luminosity
runs. When the beams are properly tuned ratios of 1.4 and 1 have been
obtained.
Under these conditions, the CTD limits would be reached at beam currents
(Ip x Ie) of 100 x 30 and 100 x 45mA**2.
The parameterization of the CTD current still has to be checked for higher beam currents.
The detector is fully debugged. The transversely polarized hydrogen target
is in operation (polarization 82%). The lambda-wheel detector is running
with the transverse target coil turned on. The longitudinal polarimeter
is working. More than 200 runs have been taken. Alignment data has been
taken.
The main problem is large synchrotron radiation background in the upper
detector. This was reduced by optimizing upstream beam bumps (EL 17-101).
Conditions were much better last night.
A systematic study, including simulation of the upstream synchrotron
radiation, would be very useful.
The positron beam current should be increased.
No major work is planned during the Christmas break.
The plan is to install the recoil detector in the next shutdown.
A shutdown in August is not desirable, as the luminosity would not be
sufficient for the transversity measurement. Another later shutdown would
then be necessary for the recoil detector.
Both polarimeters are in operation (LPOL since Friday) plot.
The TPOL could not be turned on
12.10.2003 due to problems with the cooling system. It was repaired the
next day. A hole was burnt in the LPOL lead shielding. The damage could have
been caused by synchrotron radiation when the polarimeter was accidentally
left in the beam position. The LPOL is switched off for Ie < 10mA.
The mean value of the LPOL/TPOL ratio is presently 1.07
plot Friday afternoon the ratio was
close to 1. The calibration is being improved.
Only one positron only fill was available for polarimeter studies so
far. Studies will be continued during luminosity operation.
Rise time curves are necessary in order to get an absolute calibration
of the TPOL. This requires a flat machine with solenoid turned off.
The time estimate is one week. It was not clear whether it could be
done faster. A measurement of rise time curves is not essential for this
year.
The polarimeter status should be checked by the shift screw of the
coordinating experiment. In case of problems with the transverse
polarimeter the experts should be called. Instructions will be provided.
Discussion of schedule
Operation in 2003
Continue luminosity operation with 120 bunches until at least 17.12.
Increase beam currents (Ip 65-70mA, Ie 25mA). Optimize polarization.
Change positron polarization during December maintenance day (4.12.)
if integrated luminosity on tape > 5pb-1 with Pol > 40%.
The option of running over the Christmas and New Years holidays was
discussed. In case the accelerators are turned off, efficient running
would resume in mid January.
Running over the holidays (providing shift crews and sufficient experts
on call) will be discussed within the experiments, machine division and
directorate. A decision will be made in the HERA meeting next Tuesday.
Operation in 2004
A shutdown of about 5 weeks will be necessary some time next year for
interlock tests, exchange of BU coils, maintenance and improvements.
Schedules will be worked out for a shutdown in August or end 2004/
beginning 2005. A decision will be made in the next coordination meeting
in December. The schedule will of course change in case of another
BU coil failure.
There will be no HERA meeting tomorrow.
Starting tomorrow ZEUS will be the coordinating experiment.
Date of next meeting
The date of the next coordination meeting is Tuesday, 02.12.2003 10:00hrs,
building 30b room 459.