Minutes of HERA Meeting      10.09.2004

HERA

• Six BU coils were exchanged north left. Two coils showed some green color, one was rusty. The major work will be finished next week. The activities are two days behind the original schedule.
• There is a candidate for another short BU east left. The suspected ground fault can however not be detected. The removed coils will be repaired in order to have spares.
• In the south the tunnel will be close on Monday 13.09. In the north both sides will be closed 27.09.

• There is no complete understanding how the GI NR7 vacuum chamber was damaged. The opening of the vertical emergency absorbers was enlarged in early 2002 in order to reduce the back-scattered synchrotron radiation. The water cooling of absorbers 1 and 2, not absorber 3, was turned off to increase the sensitivity to synchrotron radiation. The first incident (vacuum burst) happened on 26.06.2004. There were 10 more vacuum bursts in the following two week. Synchrotron radiation hit the GI chamber in the middle causing local heating and deformation. The hot spot moved towards the flange on the IP side during further incidents. The chamber sagged up to 5mm. One of the upper coils was damaged.
• In principle, there are two solution to improve the passive safety: 1) Go back to the original size of the vertical absorbers. This is not possible within the present schedule. 2) Galvanic coating of the stainless steel chamber, which would be too time consuming. The decisions was to leave the absorbers as they are. New absorbers 2 will be prepared for the north and south IPs.
• During this shutdown the safety will be improved by beam dump signals of new temperature sensors on the GI chamber, the BTS rate and vacuum interlock of individual pumps. Temperature alarms were already used successfully at the end of the running period. The present pump interlock includes the whole section, not individual pumps. Water cooling of absorber 3 will be turned off.

• It is being investigated whether the controlled areas are still required in the north, east and south halls.

H1

• The damage of the FST was due to a leak of the water cooling. A crimp connection of a plastic water tube failed after 3 years of operation. The leak caused serious corrosion of hybrids. The FST will be rebuilt.
• The BST has blocked cooling pipes. It will be repaired in Zeuthen. The plan is to re-install the vertex detector next summers, needs a 7 week shutdown.
• A new background monitor, one scintillator plane with PMT readout, will be installed instead of the BST pad radiation monitor.
• The absorber 4 was removed. The new absorber with additional Cu inserts will be installed. The proton and electron vacuum chambers will be welded in situ.
• The GI NR7 vacuum chamber was severely damaged by synchrotron radiation. Temperature sensors will be installed. The vacuum pressure will be monitored. In addition, the BTS counters will be connected to the electron beam dump.
• New FPS Roman pot stations were installed at NL 61, 80/81 and 90m.
• Minor repair work on the main detector is in progress. H1 will be closed as scheduled on 1.10.2004.

Schedule

• There are only minor modifications of the original schedule.
• After beam startup HERA will try to go to electron operation as soon as possible. The detailed operation (beam bake-out if necessary) will be scheduled depending on the vacuum and background conditions.

                Uwe Schneekloth