Minutes of HERA Meeting
18.11.2003
HERA
B.Holzer summarized HERA operation of last week, see transparency
- HERA delivered 7 luminosity runs last week. Operation on the weekend was
very efficient. Beams were refilled very quickly without any breaks.
Beam currents were 24 to 26mA positrons (intensity limited by temperature
at SR11) and 21 to 31mA protons (current not limited in principle).
- There was a break last week due to a GN magnet power supply trip. It took
some time to repair the power supply and to make sure that it is
working properly. Trips of GN power supplies could cause similar proton
losses as the GA power supply a few weeks ago. Fast monitoring of
power supplies is needed.
- The BPM proton beam abort was tested.
- Presently the most severe problem is the positron current limitation due
to high temperatures at the proton beam pipe flange at the absorber SR11.
At about 25mA one sensor goes up to 60deg C. The limit is 65deg C
(beam dump).
The positron beam orbit was checked. It seems not to be possible to
reduce the temperature by beam steering.
The temperature sensor will be checked during the next access.
- There were 3 trips of the proton 208MHz RF system. The system was repaired.
- The vertical angle of the proton beam at the south IP was corrected
yesterday (0.5mrad). The luminosity at ZEUS increased and is now similar
to the value at H1. The proton lifetime and backgrounds at ZEUS
also improved.
- The luminosity is still somewhat lower than expected. The proton beam
emittance is quite good (approx 15 mm mrad). The positron emittance
is worse than the design (30 to 50 instead of 22 nm). The dispersion
has not been corrected so far. The new procedure will be tested this week
during positron injection (few hour test with low positron current).
- Positron polarization is still around 30%. Harmonic bumps were used
for trying to increase polarization. Studies will continue during
luminosity operation.
- The positron beam was lost several times at the end of a luminosity run
when the ZEUS calorimeter was opened, once at the beginning of a fill
when it was closed. The reason for the beam losses is that the
automitic orbit
correction is not working properly (SEDAC error of the HO coil).
ZEUS
R.Carlin summarized the ZEUS status, see transparency
- Yesterday the positron background decreased after upstream orbit steering.
The proton background was improved significantly when the proton angle
at the IP was changed. Both positron and proton backgrounds are now
below the October extrapolation. CTD operation at IpxIe 60x50mA**2 or
100x40mA**2 should now be possible. Today the particle background was
good, but there was some synchrotron radiation background which was
reduced by orbit steering. Better monitoring of synchrotron radiation
background us needed (work in progress).
- After changing the proton angle the luminosity is now similar to H1.
- Some increased radiation mainly during beam losses was observed by
the MVD radiation monitor.
- ZEUS is considering beam dumps and possibly positron injection with
close calorimeter. Need to get clean injection and dumps first.
H1
- H1 had 8 good luminosity fills, Lint. 640nb-1. The luminosity is similar
to data taking in 1996 or 1/2 of 2000. The background conditions are
quite poor. The drift chamber is operated at its limits. There were
3 massive HV trips. The vacuum pressure is still a factor of 2 worse than
before the leak. Background conditions are getting worse.
After regeneration of NEG pumps last week, without warming up of GO/GG
magnets, the pressure improved in the straight section, but not at the IP.
The NEG pumps should be regenerated this week, including warmup of
GO/GG.
HERMES
- The synchrotron radiation background was bad (top part of detector) for
all filss, except the last one. The detector could only be turned on
2 hours after the beginning of the fill.
- Would like to ramp up the target magnet including compensator.
This will be done after positron acceleration is finished starting next
fill.
- Waiting for higher positron polarization.
Schedule
- Continue luminosity operation. Ie 20mA, Ip 30mA increase to 40mA.
- Thursday early morning stop beam operation, warmup GO/GG north and south
for regeneration of NEG pumps. Start proton beam operation late evening.
- DESY received the permission to continue operation until middle of August
and to perform the interlock tests in August.
HERMES is the coordinating experiment.
Uwe Schneekloth