Minutes of HERA/Experiment Coordination
Meeting 23.04.2004
Agenda
- Brief status reports
- Operation until summer shutdown
- Update of shutdown activities
- Discussion of long term schedule
- Date of next meeting
- AoB
Minutes:
Present Performance
- The luminosity has been steadily increased as the beam currents are
increased. The peak luminosity doubled since January. The maximum
achieved so far is 3.5 10**31 cm-2 s-1. The accelerator physics
issues have been solved. The luminosity is scaling with Ip x Ie.
The goal of 4.5 10**31 cm-2 s-1 should be obtained within a few months
as soon as 50mA of positrons can be stored. The total delivered
integrated luminosity is about 36pb-1. The integrated luminosity
has suffered from technical failures. Although the maximum daily
luminosity is 1.0pb-1, the average is only 355nb-1. The improvement
of the accelerator efficiency is presently the largest challenge.
- The present technical problems are:
- High beam pipe temperatures SR/NR with the risk of vacuum leaks.
A new absorber with additional protection of the adjacent flanges
is ready. Two absorbers with coating will be ready for the August
shutdown.
- Ground faults of the BU-type proton magnets. Not present for the time
being. Nine spare coils were ordered. The first one will be delivered
in May, first 6 coils end of June. The remaining 3 coils will probably
be here in September.
- Noise in the RF frequency generator, which is a likely source of
the coasting beam production causing severe background spikes.
Yesterday the intermediate frequency generator was replaced by a set
of synthesizers. The original frequency generator is now being
checked and repaired.
- Frequent technical failures of various components.
- Operational efficiency: improved operator training.
- The projected delivered luminosity until the summer shutdown is 108pb-1.
- Obtaining high polarization was more difficult than expected.
Before the change of the rotator position 1.04.2004 polarization was
between 30 and 40%. (50% was achieved without collisions.)
Presently it is up to 50%. The rotator settings will be checked.
- Background conditions
- HERA beam currents are no longer limited by background conditions at
H1.
- The vacuum recovered very quickly after the two 2 recent leaks and
venting of the ZEUS interaction region.
- Presently, the main problems are proton spikes. The frequency generator
and BU magnet could be the source.
Electron operation
- The expected running conditions with electron proton
collisions are based on the experience in March 1999 (all integrated
ion pumps in the arcs had been replaced by NEG pumps in 1998):
- Electron currents of 35mA, instead of 45mA for positrons.
- Beam lifetime expected to be somewhat shorter (11->8h). It is
unclear whether the lifetime will increase as a function of time.
The 1999 running period was too short to draw any firm conclusions.
- The particle background is expected to increase due to tails in the
transverse e- beam distribution.
- More frequent background spikes are expected.
- The heating NR/SR due to synchrotron radiation will be larger.
- Slightly larger proton background due to larger synchrotron radiation
load.
- e- luminosity production will be somewhat less efficient.
- The expected e- p luminosity performance was taken into account for
the different running scenarios: switching to electrons
summer 2004, Christmas break 2004/05 or summer 2005.
The total delivered integrated luminosity is about
700 +- 30pb-1, depending on the scenario.
- The machine division is prepared to switch to electrons, although would
prefer to postpone the switch until HERA has demonstrated full
performance for some time.
- From the machine point of view it would be advantageous to decoupled
switching to electrons, i.e. change of polarity and moving of IR magnets,
from the shutdown activities. One option would be to stop luminosity
operation 1 or 2 weeks before the shutdown to change polarity (electron
operation with the same orbit as for positrons) or to change the
magnet positions in addition.
Shutdown
- The shutdown dates are unchanged.
- It is not yet decided which BU magnets, other than the defective coil
NL, will be equipped with new coils.
- The machine group is offering to run between Christmas
and New Year, with a very short break for the Christmas holidays.
HERA Improvement Program
- A rich improvement program consisting of 70 items is underway.
The main items are: proton RF system, better pumping in the electron RF
sections and upgrade of the cryogenics system.
The existing manpower is sufficient. It will become critical if project
money is delayed.
- There is a general concern about the reliability and aging of
components.
Luminosity operation and backgrounds
- The delivered luminosity is 37.2pb-1. The slope is similar to 2000
with much lower duty cycle, but higher specific luminosity.
The peak luminosity so far is 3.5 10**31, compared to 1.8 10**31 cm-2 s-1
in 2000. 22.1pb-1 have been written to tape with full chamber HV.
- The high voltage efficiency spreads from 60 to 90%. For fills with long
periods of background spikes, the HV efficiency is below 50%.
- In particular for high positron current the HV efficiency is not yet
as good as in 2000. Stable running conditions are required to profit
from high luminosity. For e- p operation in 1998/1999 operation was
inefficient for electron currents above 28mA.
- The improved background conditions from February 2004 have been almost
maintained.
Stable chamber operation is now possible at Ie x Ip = 40 x 90 mA**2.
- For electrons the synchrotron radiation background in the CJC will
increase by 40%. With proper collimator setting the e-gas background will
be unchanged. The p-gas rate will increase by 15% due to increased
photo-desorption. At Ie x Ip = 50 x 105 mA**2 the expected CJC current
is 220muA, instead of 190muA for e+ p.
First HERA II Physics Results
- First physics results (polarized charged current cross section and
new events with isolated high p_t lepton and missing p_t) and
the high luminosity physics program for e+ p and e- p were presented.
Future Running
- High luminosity and clarification of the anomalies observed in e+ p
scattering is the highest priority. H1 would
like to collect an integrated luminosity of 300pb-1 before switching
to electrons.
- H1 is ready to operate the detector beyond the end of 2006 and wants
to complete the original HERA II program including e- p and low
energy running.
Shutdown Plans
- The shutdown plans are unchanged:
- Upgrade of the FPS Roman pot moving system.
- Repair of a few EM Spacal cells.
- Repair of the Central Silicon Detector and repair of a few
channels of the CIP chamber does not fit within the scheduled
shutdown and will not be done unless there are other reasons
to extend the shutdown.
Data taking
- The delivered integrated luminosity of 28pb-1 is disappointing.
The luminosity written to tape is only about 12pb-1 due to too many
HV trips of the drift chamber. The HV trips are mainly caused by
spikes in the proton background, which have been occurring for the
last 1 1/2 months. The time structure of the spikes
is being investigated. The hope is to make the CTD less sensitive.
- The vacuum pressure and background conditions recovered very quickly
from the two recent leaks.
- The detector, including the solenoid, is operating stably.
- No major work is planned during the summer shutdown.
Request for HERA II planning
- The primary goal is high luminosity data taking with e- p and e+ p.
ZEUS is requesting to switch electrons in summer 2004. If there
are serious limitations with electron running, we still have time
to investigate and fix them. Even if electron running is less efficient
we are likely to get more physics results out quicker than with
continued positron operation.
- For e- p operation background conditions should be similar to e+ p
running and will be manageable.
Data taking
- The detector is fully operative. The data taking efficiency is high.
Background conditions are under control most of the time. The target
polarization is greater than 85%. The slope of number of polarized DIS
events versus time is still a factor 2 lower than expected.
- HERMES will continue taking transversely polarized H and unpolarized
high density end-of-fill runs (D, Kr and Xe) until the summer shutdown.
High (>50%) beam polarization is important.
Shutdown activities
- Minor repairs of the detector will take 2 weeks.
- The recoil detector will be installed in a 4 week shutdown, latest in
summer 2005.
Long term schedule
- In order to obtain maximum physics output from the recoil detector,
positron and electron data are necessary. Switching to electrons
this summer and back to e+ summer 2006 (scenario 3) is the preferred
option. Switching to electrons during the 2004/05 Christmas break is
not optimized for the transverse polarization program.
Going to electron operation in summer 2005 is not acceptable.
- Both polarimeters are still running smoothly. There is however still
some discrepancy. Comparisons of the LPOL/TPOL ratios did not show
any dependence on the LPOL operational parameters. For HERA I the
TPOL was calibrated using the polarization rise-time after
depolarization.
This has not been done yet. The LPOL/TPOL ratio shows a clear correlation
with the positron beam size at the position of the TPOL laser.
- Offline analysis of TPOL data is in progress. The depolarizer hardware
has been reactivated in order to do calibration runs. If necessary,
turning off the spin rotators may be required for the rise-time
calibration. The depolarization activities will be presented and
discussed in a special meeting.
- The LPOL cavity electronics suffered from radiation damage, synchrotron
radiation emitted from the HERMES transverse target magnet. The
electronics is repaired. A two day access is needed for installation
(electronics and lead shielding) and alignment of the laser.
The date for the installation will be discussed in the weekly HERA
meeting.
- There is not much progress on a new more radiation hard calorimeter
for the LPOL cavity. Scintillators of the present calorimeter would
have to be replaced every month if it is operated continuously.
- The requirements for the west hall are: move detector out of
beam-position for fast tram access, clear separation of HERA B and HERA,
improve shielding in hall and HERA B no longer on call.
- Three different scenarios were discussed. The decision was to
leave the detector inside the interlock area: move detector into tram
position, remove vertex detector vessel and move muon detector (+x side)
outside of shielding. The activities can be done within the shut-down
schedule. Moving in the HERA tram would take 8 days.
Long Term Planning
- There was no agreement between the experiments on the date for switching
to electron operation, HERMES and ZEUS requesting to switch this summer,
H1 requesting next summer and HERA preferring to continue with positrons
until the machine has demonstrated full performance for some time.
There was a consensus that it would be better to decouple switching
to electrons from the shutdown activities.
R.Klanner said that the directorate will take a decision on the date
in the near future.
- R.Klanner also mentioned that the Scientific Council (WR) and the
Administrative Council (VR) have been informed about the proposal
to continue HERA operation until the middle of 2007. The next meetings
of the WR and VR will take place in June.
- The directorate discussed the conditions for a prolongation of HERA
operation in case of a major discovery. A document on the conditions
has been prepared.
Date of next meeting
The date of the next coordination meeting is Tuesday, 06.07.2004 10:00hrs,
building 30b room 459.
Uwe Schneekloth