Minutes from target meeting held December 7 2007 in 892-1-B09

These minutes are available also from:

http://wwwcompass.cern.ch/compass/detector/target/Minutes/2007/

a) 1.0 K empty target cell calibration from Friday November 30 23:00 to Sunday
12:00. Kaori: retune coil #9 Q-curve to center of frequency window. Take data 
with retuned coil Sunday 12:30 - Monday 11:30. No change in TE-area compared 
to before. The second empty target cell measurement gives a little higher
polarization values than Yuris asymmetry analysis for coils #2 - #7 while
for coils #1, #8 and #9 the value is little lower, see 
http://wwwcompass.cern.ch/elog/target_polar/11 . In general there is good 
agreement between Kaori, Yuri and Takuma. Takuma checked also the Yale card
gains. These are close to the values from 2006.

b) PLC CPU failure on Thursday morning 7:40.

c) Norihiro: new mircowave power supply and EIO tube from CPI expected end of
March. Power supply test planned for March.

d) Yuri: paramagnetic centers probably important in understanding of the
polarized ammonia lineshape. Cross calibration between NMR-line shift and
polarization from thermal equilibrium needed. Disagreement in coil #9 analysis,
to be understood.

e) Fabrice: liquid helium dewar on platform empty on Tuesday December 4. 
Thursday 10:00 magnet liquid helium vessel empty. Flash card to be installed
to the magnet slow control PC. Less sensitive to magnetic field induction.
During warming up of the target the helium liquefier online purifier 
regenerated every 4 hours while the oxygen level was 6 - 8 ppm at the target
platform.

f) Helium-4 pump system replacement was discussed. The oil consumption on the
roots shaft means that at least the lip seal needs to be replaced.


Comments from Fabrice:

Dear all,

Just for additional info concerning the cryogenic control of the magnet: After
an organized power cut in November in the compass hall, I could not restart the
PC managing the slow control of the cryogenics because the hard disk had
probably suffered from the large amount of magnetic cycles of the target. This
is an "industrial" PC running a real time Operating System and which has some
special features. The sensitivity to the magnetic field is probably coming from
the aluminum frame of the PC which does not constrained the field lines and
"unprotect" the hard disk. A well known solution is to replace the hard disk by
a flash memory card specially formatted for such an application.

The consequences of this crashed disk are the definitive losses of the
historical data concerning the magnet (flows, pressures, temperatures, solenoid
and dipole currents, ...). Fortunately I was well inspired to create a small
application to write online the values of solenoid and dipole currents onto a
separated support and which was running since March/April 2007.

Regards,

Fabrice