Until Saturday HERA delivered 4 luminosity fills with positron currents
of up to 40mA. The maximum luminosity was about 3.5 10**31 cm-2 s-1 at
H1 and ZEUS, the specific luminosity about 1.5 10**30 cm-2 s-1 mA-2.
Beam instabilities and blowup of the proton emittance could be avoided.
The proton collimator positions were re-optimized. The rate at the
collimators (10kHz) was much higher than normal (1-2kHz). The reason
for the proton background is still not understand, possibly a
longitudinal instability. Power supplies of the 52 and 208MHz proton
RF system are checked.
The leak at the absorber SR11 electron flange happened again on Thursday.
It reopened at the end of the next fills and could not be repaired by
gluing. The south IP was vented on Saturday and the seal was replaced.
Positron beam operation started Sunday to Monday night after the GO/GG
magnets were cold again.
Until this morning HERA continued positron beam operation for beam
bake-out, polarization studies and HERMES.
The shielding at the absorber SR 11 was reinstalled this morning.
The plan is to do one test luminosity run with small beam currents
and to continue luminosity operation with full proton current and
slightly reduced positron beam depending on the background conditions.
Polarization increased to about 40% during ep operation and up to
45% during positron beam operation.
ZEUS
After the collimator positions were re-optimized there was one fill with
perfect background conditions. In general the proton background spikes
start to appear immediately after beam are brought into collisions
at ZEUS.
ZEUS is waiting for improving the vacuum and background conditions.
H1
During luminosity operation the efficiency was very good (80% HV on).
The slope of the integrated luminosity was quite good.
Yesterday during positron beam only operation the CJC chamber current
was slightly higher than expected.
HERMES
Was very happy. The proton background improved. Data taking was
very efficiency, including the positron beam only period over the
weekend.
Polarimeter
The LPOL/TPOL ratio is now close to one. This is probably related to
a change of the positron beam size at the transverse polarimeter.
Schedule
Do a luminosity test run with small currents, 10 bunches.
Continue luminosity operation with full proton current and
slightly reduced positron beam depending on the background conditions.