hera_minutes_020507.html

HERA was not very successful in delivering luminosity last week. Collision were achieved several times, but the colliding bunches were usually lost.

There were several technical problems: broken NMR in proton reference magnet, proton beam position monitors (electronics was repaired), proton 208MHz RF system and timing system, power supply in west (being repaired today). Electron RF transmitters failed (being repaired today). Several magnets got hot on the weekend due to a broken pump of the cooling system (was repaired yesterday).
Stable positron beam was delivered to the experiments on Wednesday.
Yesterday during the machine shifts, the dynamic aperture of the electron ring was studied. It seems to be very tight. Analysis is still in progress.
Improvements of the proton RF system resulted in a better beam lifetime, shorter bunch length and smaller emittance. No satellite bunches were observed anymore. The proton background at the experiments is expected to be considerably better now.
The attempt to go to high positron currents with collisions was not successful. It was difficult to monitor the colliding bunches. In addition, the positron current was limited by the vacuum in the north IP. A leak test will be done during the access today.

During the stable positron fill (Ie=8mA) on Wednesday the background was reasonable (chamber current of central tracker 90muA), but higher than Sunday last week.
The chamber current was low during the stable proton beam Friday evening.

The CTD HV was successfully turned on during the stable positron beam run. The scaled maximum positron beam current is about 12mA.
The background was low during the proton run.
During collisions the trigger rate of off-momentum positron runs was a few 100Hz.

The detector was turned on during two long positron fills (1.05. and 3.05.). After moving in the collimators the background conditions were acceptable and scale with the conditions in 2000.

Couldn't do much because of lack of stable proton beam. On the weekend the proton background was low, much lower than the previous weekend.

After the access, stable proton beam for about two hours, continue with colliding beam operation.
Optimize background conditions and try to increase the beam intensities. Tuning backgrounds for H1 will be done first until Friday. ZEUS has priority on the weekend.
Do one single bunch positron beam run when protons are not available.
Machine studies on Monday and Tuesday.
H1 is the coordinating experiments until Friday. ZEUS will be coordinating during the weekend.

Uwe Schneekloth