shutdown including interlock test: 17.08. - 10.10.2004
startup and studies: 11.10. - 24.10.2004
luminosity operation: 24.10. - 18.12.2004
machine studies starting 18.12.2004
The positron current has been slowly but steadily increased
(about 0.1mA/day). The proton bunch currents are already similar
to 1999/2000. The machine is running close to the beam-beam limit.
It is time to increase the number of bunches.
The maximum luminosity obtained so far with 120 bunches is 2.2 10**31
cm-2 s-1.
The luminosity measured by H1 is well described by the measured beam
parameters. A reduction factor of 0.874 has, however, to be included.
The reduction is due to optical imperfections, beam ellipse tilts
and errors of the emittance measurement. A decrease of the specific
luminosity is observed during long fills. A blow-up of the proton beam
at the beginning of a run occurs about every 10th fill.
The positron beam gets unstable
when beams are brought to collisions, causing a rapid increase of the
proton beam emittance. This is not yet understood.
The specific luminosity can be improved by compensating the beam-beam
beta beat (10% improvement) and fine polishing of the optics (5-10%
improvement). Beam-beam effects will also be decreased when the number of
bunches is increased from 120 to 180. The overall improvement factor
is 1.5. The expected peak luminosity is 3.8 10**31 cm-2 s-1.
The overall efficiency (average 41.6%) is still poor due to major
technical problems. The average time between luminosity fills is
10hrs, the average fill length 7hrs. 2/3 of all fills are ended
non-intentionally.
On average the delivered luminosity is 0.335 pb-1/day.
Assuming a factor 1.8 increase of peak luminosity and 1.25 improvement
of the overall efficiency, the expected delivered luminosity for 2004
is 135pb-1.
The HERA procedures are working well. Improvements in progress are:
proton orbit feedback, automatic proton tune control, simplified
injection and acceleration.
Background tuning is very efficient due to recent tools.
High temperatures at the absorber SR can be avoided by better
orbit steering, local cooling and interlock system.
The proposal is to increase the number of bunches to 180. A new
fill pattern was discussed with the experiments reducing the number
of pilot bunches. (180 p and e+ bunches, 7 p and e+ pilot bunches.)
Technical improvement program
Preventive maintenance of power supplies has increased the mean time
between failures.
Work is on progress on the RF klystron protection circuitry.
Extensive measures have been taken to prevent major uncontrolled
proton beam losses. Two power supply failures happened since December.
Both times the proton dump was triggered by the improved alarm system.
Polarization
During collisions beam polarization is 30-40% The maximum achieved without
collisions is 50%. Further improvement plans are presented by
E.Gianfelice-Wendt.
Changing the spin rotator positions was foreseen for the March maintenance
day.
Requests
Close ZEUS calorimeter at 12GeV. Dump proton and positron beams
with calorimeter close to speed up operations. (See ZEUS presentation.)
All shutdown activities should fit in the present shutdown schedule.
Two days are required for dedicated polarization tuning.
Switching to electrons
Two weeks are required for adjusting the IR magnet positions.
In addition about two weeks are needed for beam steering and studies.
Background conditions should be studied before switching to electron
operation.
The present polarization of 30 to 40% was established in December and
January with parasitic polarization studies.
For an ideal machine with 3 spin rotators the expected polarization
is 75% without detector solenoids.
Including the H1 solenoid it drops to 70%. Including random errors
simulations give polarizations of 67.5% without solenoids, 64% with
solenoids and 57% if non-linear effects (no beam-beam effects) are
taken into account.
The observed polarization rise time is not as fast as expected from the
simulations. Beam-beam effects are not well simulated.
Dedicated studies with positrons only (optimizing betatron tunes, energy
scan and tuning of harmonic bumps) are essential for improving the
present level of polarization. More than 50% should be obtained.
There are indications for a blow-up of the positron emittance during
collisions, which could reduce the maximum polarization. Studies are
planned to understand the emittance growth.
The time estimate for the polarization studies is 6 shifts.
Changing the position of spin rotators can be done during a normal
maintenance day. Some additional time for polarization tuning will
be necessary.
Both polarimeters, LPOL and TPOL, are running with minor problems.
The LPOL/TPOL ratio increased from 1.07 to 1.12
(figure ). Systematic studies
are in progress to understand the discrepancy.
The LPOL cavity was locked with the HERA beam. Bremsstrahlung spectra
have been recorded. Significant synchrotron radiation background from
the transverse target magnet is seen in the sandwich calorimeter
introducing a large pedestal shift
(figure ).
It is planned to use the beam scrapers in the east straight section
to shield the calorimeter against synchrotron radiation
(figure ).
Water cooling will be connected to the scrapers during the access day
next week. It is however important
to assure that the collimator jaws will not get too hot.
Both LPOL calorimeter give similar polarization values. So far no reason
for the large ratio has been found. Spare parts for the laser
arrived.
Systematic studies of the TPOL hardware give no clear indication
for the large ratio. The offline analysis gives the same polarization
values as online, although with unreasonable linear light polarization.
Figures:
tpol correlation ,
table .
Reanalysis of the CERN test beam data is in progress to check the
analyzing power.
Rise-time calibration curves will be mandatory if the reason for the
large LPOL/TPOL difference cannot be found using the current data.
No dedicated time will be required if the measurements can be done
with a non-flat machine, otherwise the rotators have to be turned off.
The depolarizer has to be recommissioned.
The delivered integrated luminosity is 22.6pb-1. 21.0pb-1
have been written to
tape, 12.2pb-1 with full HV. At the beginning of a fill the
specific luminosity is typically 1.3 10**30cm-2 s-1 mA-2, dropping
to 1.3 10**30cm-2 s-1 mA-2 at the end of the fill. Spiky background
conditions are now the main reason for the reduced HV efficiency.
The beam gas background rates decreased by a factor of 4 since November.
The chamber currents achieved in February allow operation at design
beam currents. HERA operation is no longer background limited.
The CJC HV was recently increased to get slightly higher hit
efficiency and dE/dx resolution.
A big improvement of the proton rates was observed after the NEG
regeneration in February. A slow increase has been observed recently.
NEG pumps should again be regenerated next week, including warm-up
of GO and GG.
The synchrotron radiation background in the CJC is now a factor of 2
smaller than in 2002, mainly due a better alignment and beam steering
and installation of lead shielding in the backward region.
Plans
H1 is ready to run with 180 bunches and 90mA proton current.
The positron current is expected to increase from 35 to 50mA in
small steps.
The chamber trip levels will be increased at high beam currents.
The proposal is to switch to left-handed positrons at the maintenance
day next week.
Further machine studies should be done to understand and improved the
specific luminosity.
The priorities are: 1)highest luminosity, 2) high duty cycle and
stable running and 3) high polarization.
The shutdown activities are: Upgrade of FPS Roman pots at NL 61,80
and 90m.
Repair of EM SPACAL cells. The central silicon
detector will not be repaired, as it requires breaking the vacuum.
All shutdown work can be done within 5 weeks. The repair of the
BU magnets needs to be coordinated with the machine group.
H1 prefers to continue high intensity e+p running aiming for
another 250pb-1 until summer 2005.
The delivered integrated luminosity
since January is 12pb-1. The gated luminosity is about 5pb-1 (HV on).
All detector components are working.
The background conditions have improved significantly. The detector
can be turned on at design beam currents.
Recently, the data taking efficiency suffered from spiky background
conditions (instability of positron and proton tunes, beam emittance
growth).
Since January occasional fast discharges of the solenoid occurred
without any apparent reason. The ground connection of the power
supply was improved. Operation is much more stable after the
exchange of several relays. A major overhaul of the electronics
(quench protection and power supply) is planned for the summer shutdown.
In the future the calorimeter will be closed when proton acceleration
is finished. A modification of the interlock electronics will be completed soon. Beams can then be dumped without opening the calorimeter.
The injection veto cannot be overwritten by HERA.
Plans
Prefer not to change the spin direction next week to avoid disturbance
of machine operation and understanding of polarization.
Increase number of bunches to 180.
A decision on switching to electrons should be taken soon.
Decision of whether or not running over Christmas should be taken before
this summer.
HERMES has been taken data with high efficiency. The spectrometer is
fully operative. The target magnet is now ramped up before luminosity
running is declared.
About 1.9 10**6 transversely polarized DIS on H and a similar number
of unpolarized DIS during end-of-fill runs have been accumulated.
Large asymmetric synchrotron radiation background was observed until
a few weeks ago. It is much lower now.
A big effort is expected to improve beam polarization.
There are no objections to changing the spin rotators, although it
should not have any impact on the stability of HERA and should not
compromise increasing polarization.
Plans
The recoil detector will be ready
for the summer shutdown, installation would take 4-6 weeks.
The decision whether it will be installed depends on how long HERA will
be in operation. A data sample of 7 10**6 transversely polarized
DIS with reasonable polarization is required. Both electron and positron
data should be taken with the recoil detector. The preferred schedule
is: run until summer 2007, switch from positron to electron operation
summer 2004, installation of recoil detector summer 2005 and switching
back to positrons in fall 2006.
Moving HERA B out of beam position
K.Sinram summarized the present planning for moving HERA B out of the
beam position. There are two options:
Move the detector to the parking position, rebuild the shielding
as it is now. The time estimate is 5 weeks. Moving the HERA tram
into the tunnel would take about 1 week once the detector is in the
parking position.
The disadvantage is that the hall would remain a controlled area.
Disassemble the detector and rebuilding of complete shielding.
This would take 8 to 9 week, i.e. longer than the schedule shutdown.
Access to the tunnel would take 4 weeks.
Another option would be to start removing the electronics hut before
the start of the shutdown.
R.Klanner and D.Trines will contact HERA B and MEA.
Schedule
Increase number bunches to 180 as soon as possible.
Two days of dedicated polarization studies will be performed after
the maintenance day next week.
The spin rotators will be moved during the April access day (01.04.2004).
The long term schedule, i.e. end of HERA operation and date for switching
to electron operation, will be discussed in the next coordination
meeting.
This week HERMES is the coordinating experiment.
Date of next meeting
The date of the next coordination meeting is Tuesday, 20.04.2004 10:00hrs,
building 30b room 459.