hera_minutes_030128.html

Positron beam bake-out at 12GeV was done last week. The current was limited to about 32mA by a maximum beam pipe temperature at H1 of about 70deg C. No significant improvement of the vacuum was observed at the north IP. During the positron beam bake-out proton beam was kept in the machine for HERA B. There were only 2 interuptions in operation due to technical problems.
The positron beam intensity was increased during 2 shifts. The beam loss effect observed a few weeks ago has disappeared (not understood).
A positron current of 40mA was accelerated to 27.5GeV and stored in HERA for 2 hours without problems. The current was limited by the temperature at the ceramic windows of the SC cavities. It is presently difficult to go to higher currents. The hope is to reach 45mA. Safe operation above 50mA requires repair of the SC cavities, which is planned for the shutdown.
The GO/GG magnets were warmed up yesterday. It was not possible to keep the proton beam during the warm-up. The proton background was too high at H1. NEG pumps were activated (north) and regenerated (south IP). GO/GG are being cooled down today.
HERA is ready to resume luminosity operation.

HERA B data taking was very successful, see number of collected J/Psi. Last night 12000 J/Psi events were collected per shift, 1380 J/Psis /h compared to typically 30 events/h in 2002. The detector is in good state. The J/Psi is slightly higher than expected.
The target rate was relatively unstable. The tungsten wire which is presently used (so called emergency wire) is not well adjusted. It will be replaced during the maintenance day next week. The wire thickness will be increased from 50 to 100um. Replacing the wire will take 2 shifts, one night of pumping and final leak test the next day.

During the bake-out the positron current was limited by the temperature of the H1 beam pipe. 75deg C is the maximum temperature. A decrease of the BTS background rate was observed during the bake-out. The background monitor was unstable on the weekend because of a high radiation dose. It is stable again after reloading the thresholds.
The background rates decreased during the cool-down of GO/GG this morning.
Warming up of the solenoid will take 10 days. It was proposed to do polarization studies in the last week before the start of the shutdown when the solenoid is not needed.

During the bake-out a high pressure increase was observed close to the IP. The pressure increase decrease slightly as a function of time.
For the next few days the positron current should be limited to 15mA in order to do HV studies of the CTD.

Continue luminosity operation, starting with Ip=15mA, Ie=35mA. After a few days increase beam intensities. If no collisions are found within 30 minutes continue with separated beams (no collisions).
The proposed shutdown activities will be reviewed. The first review, modification of ZEUS C5 collimators, will take place Friday at 9am.
The access Thursday next week will be extended to Friday for the replacement of the HERA B wire.
H1 is the coordinating experiments.

Uwe Schneekloth