Minutes of HERA Meeting
14.01.2003
HERA
- The last luminosity fill was on Tuesday. After this it was no longer
possible to store high positron currents in the machine. At currents
above 25mA it takes 2 to 15 minutes until the lifetime gets very poor
and the beam is lost or dumped by the experiments. Very high background
rates are observed at HERMES and ZEUS.
The effect only occurs at high currents. Several shifts were spent
trying to find the reason for the beam losses. A similar effect
behavior was present in November. There are indications that the
source is in the south straight section.
- Friday afternoon there was an accident involving the quench protection
system.
A PLC, control of the dump switches in the west, broke. The stored energy
of 250MJ was dumped into the dump resistors west right. This was
caused by an error in the communication between the PLCs.
Some parts of the tunnel got hot and was covered with slag.
The dump resistors were replaced yesterday. The tunnel was cleaned. The
electronics was repaired. A final test is done today.
- Two leaks at the north straight section occured on Saturday (NR14, flange
between GM magnets) and Sunday to Monday night (NR11, flange of main
absorber). Tightening the bolts was not sufficient to seal the leaks.
Glue was used in addition. The leaks were caused by bad beam orbits,
illuminating part of the beam pipe with synchrotron radiation and
resulting thermal stresses.
Temperature sensors will be installed to monitor the temperature at
critical flanges.
- The wire of the electron machine wire scanner was broken. It was repaired
yesterday. 1 to 2cm of the wire was missing. It unlikely that the broken
wire was the reason for the beam loss effect.
HERMES
- The positron timing is stable again.
- The magnet was unstable during some tests, which were performed
without notice.
ZEUS
- Last week the MVD radiation monitor received a dose of 8krad.
Schedule
- Today: final tests of quench protection system. Inject low current
positron beam.
- Try ep collision with 20 x 20 mA.
- Continue study of positron beam losses.
- High positron currents on Thursday.
- HERA B is the coordinating experiments.
Uwe Schneekloth