Last week was very rough. Luminosity was delivered until Thursday
evening. The machine group tried to get the longitudinal proton beam
instability under control by modulating the 208MHz RF voltage.
After this the situation was very bad, very large coasting beam
production.
Luminosity operation was interrupted on Saturday in order to find the
source for the coasting beam production. Some correlation was found
between ramping the electron magnets and the increase of coasting beam.
It was tried to run without the 208MHz system. On Sunday afternoon
a preamplifier of the 208MHz system A broke.
The coasting beam production was back to normal, about 2-3mA at the end
of a long luminosity fill, after it was replaced.
Irregular behavior of the cavity voltage is no longer observed.
New diagnostics for the RF system is in preparation.
In general, background conditions are still critical at the end of fills.
Better optimization of the collimator positions and beam tuning upstream
of the interaction regions is necessary.
The coasting beam production is now similar to the situation in
1999/2000.
There was some discussion whether the collimator system could be
improved,
e.g. a more transparent collimators or the use of HERA B wires.
The coasting beam kicker, which was in operation in 1999/2000, was
too weak, the bandwidth not sufficient. In addition, some part of the
beam was excited.
Improvements of the RF system are being considered (improved filtering,
better RF reference).
The first goal is to improve the background
tuning by better operator training (collimator optimization).
The proton bunch length is rather large. A blow up is observed at 600GeV
(coupled bunch mode). It is driven by narrow impedences. The impedence
mismatch will be improved when the HERA B vertex tank is removed during
the shutdown.
Positron polarization is quite high, reaching 50%. 53% was achieved
this morning. Some (5% level) improvement is still possible by doing
beam based alignment and fine tuning. The progress on the BBA is slow.
The currents for the opposite rotator position are recalculated.
The overall efficiency has not improved. At the beginning of a fill
the specific luminosity is about 1.3 10**30 cm-2 s-1 cm-2. It was
1.6 10**30 three weeks ago. Some retuning of the machine is necessary.
A small leak NR developed on Friday after dumping a high current (46mA)
positron beam. The pressure is at several 10**-10mbar. The leak is
most likely at the electron beam pipe flange of the absorber NR11.
It case the leak rate becomes more serious it will be sealed using
vacseal.
The communication between the HERA control room and experiments was
discussed. One suggestion was using conference calls.
In case of bad background conditions experts from the experiments
should be in the HERA control room.
H1
In general the situation is quite good, except on Saturday when
the proton beam orbit was off far upstream of the IP causing high
proton background.
There are no problems when the coasting beam is 2mA.
The CJC1(2) current limits were increased to 210(250)muA for high
positron currents (Ie>40mA).
The access on Friday was used to work on the FPS. Both FPS and VFPS are
operated routinely. They are not at the final positions.
Longer fills are preferred, i.e. starting the HERMES high density run
at less 20mA.
There were no major ZEUS hardware problems. The main problem is still
background spikes tripping the CTD. Almost no luminosity was taken
Thursday to Sunday.
The timing structure of the spikes
was studied. There seems to be two types of spikes: sharp (<4ms),
mostly single peak spikes and longer spikes with some ringing.
HERMES
Smooth data taking. Proton spikes are observed during normal data taking.
The proton background is still very high at injection. This will be
improved by HERA (local orbit steering).
There is a small problem with the target gas analyzer. In case of a
break HERMES would like to go in for repair.
Schedule
Continue luminosity operation. Start HERMES high
density runs at Ie=20mA. No depolarization studies until hardware is
checked.