HERA delivered about 3.7pb-1 in 8 luminosity fills last week.
There were several hardware problems: a fake quench alarm, 3 electron
transmitter problems, a leak at the absorber SR11 and 2 proton RF
failures.
Only one 52MHz proton RF system was in operation for a few fills,
causing some satellite bunches and somewhat higher proton background.
Both proton RF systems were repaired and are now in good shape.
Last week a leak at the electron flange at SR11 occurred after a
beam loss.
The pressure increased to 10**-7mbar. It was fixed on Friday by using
vacseal. Another leak at the same flange happened during the meeting.
It was again repaired by vacseal.
The positron current should presently not exceed 40mA in order to
avoid high temperatures and further leaks.
Procedures were reoptimized.
The positron injection efficiency was improved.
The proton beam orbit was retuned, decreasing the number of
background spikes.
A new lumi file was prepared. Fine tuning of the positron orbit is still
needed. A new procedure was developed in order to avoid a blow up
of the proton beam emittance: increase vertical positron emittance
before collisions, collide at H1 (beams separated at ZEUS), collide
at ZEUS, decrease positron emittance again. A specific luminosity
of 1.6 10**31 cm-2 s-1 mA-2 was achieved at H1. There was no significant
decrease. Going to luminosity optics at the end of positron acceleration
still needs to be tested.
Operation was disrupted by 3 power glitches (Saturday, Sunday and Sunday).
Recovery from the power losses was quite fast.
ZEUS
The solenoid tripped once last week. Diagnostics had been disconnected
before. Cables for monitoring were still connected which could have
introduced noise. There have been no further trips.
It is not yet clear why the positron beam was dumped last night.
The detector HV could not be switched on last night due to high
proton backgrounds. There was a lengthy discussion whether rules
should be established for dumping the proton beam. A proposal will
be made next meeting.
The new electronics for the calorimeter injection inhibit is ready.
Beams can now be dumped with the calorimeter closed. Positron
acceleration with calorimeter closed should be tested with small positron
current.
H1
The detector is in good shape, but still suffering from background spikes.
Turning on all HVs is now faster.
New correction was applied to the luminosity measurement. The online
value will increase by 7%.
HERMES
The target was repaired during a 3 hour access last week. In general,
background conditions are fine, although the TRD rates have to be tuned
at the beginning of each fill.
The display in the HERA control room will be improved.
Polarimeter
The depolarization kicker is working. To be tested with beam.
A meeting will be held to define the parameters.
A scraper scan (OR36) was done last Tuesday with small positron current
in order to understand
the source of the synchrotron radiation background in the LPOL cavity.
The background was reduced significantly when the scraper was moved
in (8mm distance to the beam).
The cooling of the scraper is however not sufficient for full beam
current. A new collimator is in preparation.
Lead shielding will be installed during the next maintenance day
to protect the electronics. A short access some time this week
was requested in order to remove dosimeters.
Schedule
Continue Luminosity operation.
The position of the spin rotators will be changed during the
maintenance day next week.