Minutes from target meeting held September 16 2011 in 892-1-B09

These minutes are available also from:

http://wwwcompass.cern.ch/compass/detector/target/Minutes/2011/

a) Start to polarize on Friday September 9 noon and continue until Saturday
14:00. Polarizations of -88.6 %, +86.8 % and -84.1 % reached before going to
frozen spin mode. Field rotation done from solenoid +646 A to -646 A (2.5 T).
During the field rotation the trim coil B1 was set to zero current and voltage
and the power supply was switched off. 

b) Last normal solenoid current read on Sunday 10:40. After this slowly
decreasing current observed from DCCT. Alain with help of Saclay experts:
let the solenoid current decrease to -230 A. After this start to ramp
up the dipole field first to 100 A. Try to mimic the normal field rotation
as close as possible. When the dipole current reached 450 A the solenoid
power supply was put into local mode and reset. After this 1 T field rotation
was done and finally the field was raised from 1 T to 2.5 T (+646 A). 
Practically no polarization was lost due to the slow discharge. See comments 
40017, 40024 and 40029 in http://wwwcompass.cern.ch/runLogbook/dirphp

c) After recovering the 2.5 T field on Sunday the normal Q-curves did not 
show up. Unmount the Q-meter varactor diode power supply and check the 
voltages. After remounting the normal baselines could be seen again except 
for coil #4 where it seems to be shifted. See
http://wwwcompass.cern.ch/elog/target_polar/137

d) On Monday afternoon meeting to discuss the recent magnet repair, tests and
the status of the trim coils. Alain: the loss of trim coil G1 happened most
likely during the power cut of July 10. See more details in the weekly reports
of September 16.

e) Start to polarize on Wednesday 14:30. Polarization increased from -85.5 %,
+84.3 % and -81.8 % to -88.9 %, +86.1 % and -82.9 % by 21:20. Fit exponential
growth function to the build up. At least 24 hours of continuous pumping of
microwaves is needed for 90 % polarization values. With the microwave 
parameters used the downstream cell polarization is increasing slowly compared 
to the upstream.

f) Fabrice: the trim coil G1 status could be tested by observing shift in
frequencies of nearby NMR coils. Now equal polarization build up is difficult
for both up- and downstream cells due to less homogeneous magnetic field.
New trim coil settings could be tested to compensate this. The old trim coil
power supplies (ET systems) need maintenance. Some of the displays do not work,
current is not regulated correctly or the supply can not be controlled 
remotely.

g) Norihiro: unmount remote controlled microwave attenuator motor coupling
piece during the field rotation on Thursday together with Takahiro. The motor
axis is bend due to the strong magnetic field. 

During the start up of the microwaves on Wednesday an interlock prevented 
the normal start. Probably the emergency stop contactor needs to be replaced 
with a new one.

h) Plot SPS period P4 average target cell polarization. See
http://wwwcompass.cern.ch/elog/target_polar/135

i) Integrated areas and first moments from June 15 to September 13 2011
http://wwwcompass.cern.ch/elog/target_polar/136