Minutes of HERA Meeting
23.04.2002
HERA
The plan for last week was: vacuum "bake-out" with high intensity positron
current at night, trying to collide beams during the day and machine
studies on Monday and Tuesday.
- First the positron current was limited to 13mA (at 12GeV) by the
vacuum in the interaction regions reaching 10**-6mbar. The pressure
increase was probably mainly due to gas desorption off the cold surfaces
of the GO and GG magnets caused by higher order losses.
The maximum current at injection is presently limited to 23mA by the
cooling of the normal conducting cavities.
- Beams of about 10mA protons and 7mA positrons were brought to collisions several
times. Collisions are now achieved routinely, although the procedure is
still somewhat complicated. Improvements of the software are in progress.
The duration of the luminosity fills was limited. There was not enough time
to go through a full optimization of background conditions.
The proton collimator positions were optimized only once.
- The measurements of the dynamic aperture were confirmed. The roll angle
of the GO magnets in the north and south IRs was checked. The positron
injection efficiency was increased to 86%.
- Proton beam operation is not possible at present. A UPS for the cryo
system in the south straight section is defective. The repair will start
this afternoon.
- The wire alignment system in the south hall is now available.
ZEUS
- Luminosity measurement is available since Friday. The specific luminosity
is similar to the one measured by H1.
- The background conditions are still high during collisions. The high
voltage of the CTD was limited to 90%. The events which were taken have
a significant contribution of halo proton and off-momentum positron
events.
H1
- The CJC was at full HV during collisions. Above Ie = 2mA the chamber
background is dominated by positron beam background. At about 4mA the
current is close to the limit. The chamber tripped several times because
of proton background spikes.
The forward tracker was not at full HV. The outer muon detectors have
high background rates. A high rate of off-momentum positrons is observed
in the SPACAL (ring inside). The proton background is dominated by
halo protons hitting the collimators at 80cm and 1.5m right of the IP.
HERMES
- Still waiting for positron beam. The fills were not long enough to
optimize for H1 and ZEUS and to turn on HERMES.
HERA B
- The detector was switched on Friday night, took beam gas data. Planning
to repeat this for the next proton fill. Still no regular shift crew.
Schedule
- After repair of the UPS in the south hall, try to collide beams during
the day, vacuum bake-out with high positron beam during night shifts.
- Machine studies on Monday and Tuesday. The program will be discussed
tomorrow at 11:00hrs.
- Do a luminosity beam scan and test the wire scanner to determine the
specific luminosity.
- Note, added after the meeting. The meeting of the HERA task forces
proposed to continue machine studies until Friday.
- H1 is the coordinating experiments.
Uwe Schneekloth