The BU magnet ground fault did not reappear. The main problem is
strong production of unbunched proton beam during luminosity operation.
Two measures were taken to reduce the unbunched beam. They are only
effective for the first couple of hours of a fill.
On Thursday the intermediate frequency generator, a possible source for
the production of unbunched proton beam, was replaced by a farm of
external synthesizers. Some of these have noise problems.
The original frequency generator is being repaired and will be reinstalled
during the maintenance day next week. The hope is that this will
cure the coasting beam production.
Conditions should then be similar to January/February.
4 proton beam losses occurred due to ghost alarms of the quench
protection system.
The source for these fake alarms has not been found yet.
A few other beam losses happened due to trips of the proton RF system.
At the beginning of the weak the coasting beam was about 5mA at the
beginning of luminosity operation. The RF voltage is increased today
to reduce the sensitivity to noise. At present it is reduced during
acceleration to decrease beam instabilities.
In general, the initial luminosity was quite good (3.2 10**31 cm-2 s-1
last night). After a few hours the specific luminosity usually decreased
from 1.5 to 1.3 10**30 cm-2 s-1 mA-2. More fine tuning is needed.
The "new" luminosity procedure, collisions at H1 before bringing beams
into collisions at ZEUS, was abandoned. Beams are again brought to
collisions at the same time. This was possible after improvements of the
optics and reducing of the angle of the beam at the IP.
Polarization was around 40%. There was no polarization tuning due to
the proton background problems.
Data taking was usually OK at the start of fills, but degrading fast
due to frequent proton spikes causing CTD HV trips and very inefficient
data taking. The number of CTD trips is clearly correlated with the
amount of coasting beam and the proton lifetime. Data taking is impossible
for lifetimes < 50hrs (<100hrs last night). CTD trips are correlated with
spikes in scintillation counters on the fast ZEUS online monitor,
typically
one 0.2s bin. The time structure of the spikes has been studied. They
last for about 15ms showing a double peak structure.
A 300Hz structure is seen. This is particularly visible at inejction.
F.W.: The time
structure of the BU ground faults is somewhat similar, but shows
no double peak structure.
Measures are underway to reduce the CTD sensitivity to short background
spikes.
The GO/GG magnets should be warmed up, NEG regenerated next week to
reduce the base background.
H1
Data taking improved a lot after tuning on Friday. It gets much
less efficient after 6-8 hrs (Ie about 20mA) due to proton spikes.
The time structure of the spikes in being investigated.
An increase in the vacuum pressure, lumi e gas rate and chamber
current was observed when the GO/GG shield temperature temporarily
increased by 6K, indicating a high gas load on the cold surface.
The GO/GG magnets should be warmed up, NEG regenerated next week.
HERMES
Successful data taking. The turn-on procedure was changed. TRD
rates are now available early for background tuning. Trigger prescales
were changed when the proton background was high.
Schedule
Continue luminosity operation with shorter fills. Start HERMES
high density run at Ie=20mA.
Fire TSPs after fill with increased positron current.
The maintenance day next week (6.05.) will be extended to about 24hours
for warmup of the GO/GG magnets and regeneration of NEG pumps.
The intermediate frequency generator will be reinstalled.