Minutes of HERA/Experiments Coordination Meeting Wednesday, 08.05.2002
_________________________________________________________________________
Agenda
- Present status
(Progress on HERA commissioning, understanding of background conditions,
work of HERA task force,...)
- Strategy for improving background conditions
- Postpone May shutdown
Conditions/date for switching to electrons
- Plans for and preliminary date of Christmas break/shutdown
- Date of next meeting
- AoB
Presentations:
HERA F.Willeke transparencies
The electron machine is in reasonable condition after replace-
ment of a defective quadrupole magnet. Polarization tunes at
luminosity conditions are still a problem.
The positron beam currents are limited by the vacuum in the
north interaction region (NR); maximum currents so far 31mA at
12GeV, 22mA at 27.5GeV.
Conditions are good enough for initial luminosity operation
with up to 20mA.
The proton beam optics is in good state. The beam is more un-
stable at 40GeV than before. There are breakdowns of the
lifetime at 64GeV. The maximum beam current accelerated to
920GeV is 45mA.
Luminosity operation is still difficult and not yet routine
operation. The measured specific luminosity is 0.9 to 1.4*10**30
cm-2 s-1 mA-2. HERA operation has been relatively inefficient
because of technical failures.
Background conditions at H1 and ZEUS are still very high and
have to be understood.
H1 D. Pitzl transparencies
Doing two-person shifts since March. Background conditions are
still very high, main source is backscattered synchrotron
radiation. There was one luminosity run with trackers on
(Ip=34mA, Ie=4mA). The maximum specific luminosity is 1.3*10**30
cm-2 s-1 mA-2.
ZEUS W.Zeuner transparencies
The ZEUS detector was switched on for short periods of time
with full HV on the inner tracker with machine currents of 3.5
mA of e+ and 9mA of protons. However, extrapolating the obser-
ved chamber currents, save operation is currently possible
only up to about 10mA for each beam.
The main source of background is synchrotron radiation,
hitting the absorber at -80cm. There are indications that the
radiation is reflected from -11m. Another source of background
are off-momentum positrons, hitting the inner part of the rear
calorimeter.
Recently also large proton background was observed. In a dedi-
cated p-only run it should be checked that last weeks improve-
ments of the p- RF systems reduced this background to a
tolerable level.
Radiation damage of the micro vertex detector is still a con-
cern. Up to now a dose of about 20 kRad has been received.
HERMES M.Bouwhuis transparencies
The beam loss monitor is fully functional, but not connected
to the beam abort kicker.
The Lambda wheel detector was installed in March and is being
commissioned.
Background conditions are acceptable, slightly higher than in
2000.
HERA B A.Spengler transparencies
The target operation just before Christmas 2001 allowed HERA B
to start the debugging and calibration of the detector. All
means to continue along this path without new data have been
exhausted, therefore we have a strong interest to collect more
data (at the level of 8 hrs per week). However, theses requests
have to be scheduled in a reasonable way in order not to
hamper the efforts of the machine crew to bring Hera into
operation.
Polarimeter T.Behnke
The polarimeter upgrade is finished. Both polarimeters are
ready. Should be able to measure polarization with a few %
error.
The installation of an optical cavity, upgrade of the longitu-
dinal polarimeter is planned for January. Two weeks are needed
for the installation.
HERA performance/Background conditions
D. Trines said that regular meetings are now being held to improve the perfor-
mance and to reduce the rate of technical failures. The effort is concentrating
on the water cooling system, superconducting magnets at IRs and quench protection.
Bi-polar chopper will be built (power supplies of superconducting IR magnets).
In order to make progress on the synchrotron radiation background, it is planned
to do one week of dedicated background studies, mainly during day time, and
to provides stable beam for HERMES and HERA B during night shifts. Details
will be discussed in the weekly HERA meeting next Tuesday.
Plans for Christmas break/shutdown
HERA A break of PETRA operation from 06.01. to 21.02.2003 is presently
foreseen.
Added after the meeting: The work scheduled for the extended September
maintenance day requested in the meeting will be done in January.
H1 Installation of the Very Forward Proton Spectrometer, ready in January.
Repair (replacement of electronics) of central inner proportional
chamber. Time estimate for both items 10 weeks.
ZEUS Repair of the yoke under-carriage would take 4 weeks.
HERMES About 2 weeks. No major activities.
HERA B About 2 weeks. No major activities.
Conditions/date for switching to electrons
U. Schneekloth made the following proposal:
Time constraints:
not during summer
at least 2 months before Christmas break/shutdown
HERA parameters:
L > 2.0 10**31 cm-2 s-1 (maximum achieved in 2000) and
Lsp > 1.6 10**30 cm-2 s-1 mA-2 (design value - 10%) and
Backgrounds acceptable if scaled to Ip = 100mA, Ie = 50mA
If all 3 conditions are achieved until beginning of September, switch to
electrons in September. If not, continue with positrons until Christmas
break/shutdown.
F. Willeke proposed to run without interruption until the Christmas shutdown
and to switch to electrons in January.
In view of the present situation, i.e. readiness of HERA and poor background
conditions, there was no decision on the date or conditions for switching to
electrons. It will be reconsidered in the next HERA Coordination Meeting in
September.
Date of next meeting
Every last weekly HERA meeting of the month will be an extended meeting with
spokes person of the experiments and members of the directorate present.
The date of the next coordination meeting is Monday, 02.09.2002 10:00hrs
Uwe Schneekloth