hera_minutes_021105.html

F.Willeke summaried HERA operation of last week plot of beam currents

HERA managed to collide beams with polarization tunes. After minimal tuning the specific luminosity was 1.4 to 1.5 10**30 cm-2 s-1 mA-2. There was no difference whether beams were colliding at both or only one IP.
Since Wednesday HERA started delivering luminosity without polarization tunes. Beam currents were relatively low, about 20mA. The specific luminosity was 1.8 10**30 cm-2 s-1 mA-2.
There were only a few technical problems, no major ones. The 8th electron RF station will be turned on again soon. The water cooling of the cavities (a plunger overheated a week ago) will be improved.
Wrong lumi files were used twice causing some confusion.
After loading the luminosity file, luminosity was immediately obtained at ZEUS. It was usually very difficult to get luminosity at H1. It is not absolutely clear whether this is due changing beam positions or problems with the luminosity monitor. An H1 lumi expert should be present in the HERA control room at the beginning of the next fills.
Operation has been relatively stable. HERA will slowly increase the positron current.

No major problems. The CTD HV could be turned on (95% of nominal HV) at the beginning of most fills. The present current limit is about Ip*Ie = 600mA**2
Early Sunday morning the electron collimators were moved in at 25 GeV, causing high radiation background in the MVD.

The main problem was a radiation monitor, Si pad detector, which was damaged on Sunday during positron injection. The HERA injection efficiency was very poor. Another pad detector is now used for radiation monitoring. It is the last one, which is still alive.
The solenoid was off since Sunday. It was repaired today.

Beam conditions are fine. 35000 DIS events were taken last week. Higher positron currents are needed.

The time spent on production running has increased significantly. Conditions were ideal on Sunday; 57% of 24hours were used for physics data taking. This is the first time HERA B has taken long runs of up to 8 hours without any problems. Clear mu mu J/Psi peaks are seen online. In total 15 10**6 lepton pair triggers were taken. HERA B should be able to collect the data sample expected for this running period if the conditions continue as last week. A display of the data taking efficiency amd collected data sample is now available.
Background spikes were observed during positron injection. Spikes also occurred during movement of the ZEUS calorimeter and insertion of the H1 FPS. They are no major problem.
For the tungsten wire the interaction rate is more stable during collisions.

Although the proton background for proton only runs has decreased since the temperature of the GO/GG beam pipe was increased from 50 to 110K, there is no indication for a decrease of the ZEUS CTD chamber current during ep operation. The reason is that the pressure close to the IP SR is better for proton only fills. During ep operation the pressure SR IR to 30m has not improved.
The H1 CJC current, normalized to the beam currents, is now slightly worse than before increasing the GO/GG beam pipe temperatures.
After the access, the GO/GG beam pipes will be operated at room temperature. They will be cooled down again after some running.

Various vacuum activities during the access today and tomorrow: bake-out of pumping station, RGA analysis, warmup of GO/GG beam pipes, regeneration of NEG and Ti pumps.
The interlock should be set by tomorrow noon. The tunnel will be closed at 15:00hrs. Beam operation is expected after 18:30hrs.
HERA will continue luminosity operation with the conditions defined last week. The positron currents will be increased.
Some machine studies, a few hours during injection, are planned for next week.
HERA B is the coordinating experiments.

Uwe Schneekloth