Minutes from target meeting held October 13 2006 in 888

These minutes are available also from:

http://wwwcompass.cern.ch/compass/detector/target/Minutes/2006/

a) Norihiro and North Area operators: helium liquefier compressor was changed
on Tuesday October 3. On Thursday night the online purification cycle went 
from the normal 12 hours to 3 hours. Each warming up and rinsing of the 
purifier consumes helium and this gas needs to be cleaned separately before 
it can be used for production of liquid helium. Low stock of pure helium gas 
during the weekend October 7 - 8 made the liquefier operation critical. 

b) On Monday October 9 the returning helium gas was analyzed with Teledyne 
3000T. 35 ppm oxygen impurity was found in the total flow from the magnet
and dilution cryostat. After the dilution cryostat helium pumps 80 ppm was 
measured with the flow of 140 mmol/s. The gas flow from the magnet was the
nominal 2 x 0.4 g/s or 200 mmol/s. Thus after adding the separator and screen
flows the total target consumption was about 400 - 450 mmol/s. This corresponds
to liquid helium consumption of about 30 - 35 l/h. The liquefier was boosted 
with the online LN2 purifier to 100 l/h capacity in August 2001.

c) On Wednesday October 11 the helium return from the pump system was separated
from the magnet return. Now the magnet, dilution cryostat separator and screen 
flow gas is returned to the liquefier as pure gas. About 16 ppm oxygen impurity
is observed in this gas. The gas from the pump system is collected for offline 
purification. Fabrice: North Area operators will analyze sample of returning 
helium gas to find the origin of the impurity. Norihiro: during field rotation
the online purifier pressure drop increases due to large evaporation of helium.

d) The target polarization was restarted on Wednesday October 11 at 18:00 and
was continued until Thursday midnight. The initial polarizations were
-47.7 %, +54.6 % and -48.5 %. Final values were -48.1 %, +55.1 % and -49.5 %.
Yuri: the polarization difference between positive and negative cell is now 
104 %. The record value is 106 % so we are within the present error at the 
highest polarization. More experiments in setting the microwave parameters are
needed. The 8 h field decay due to SM1 makes the frequency tuning difficult.

e) Kaori showed results from the September and July TE-calibrations. The error
in the polarization is typically 1.5 - 2.5 %. For coils #1 and #4 it is 
clearly bigger up to 8 %. 

f) Target removal for the hadron run was discussed. Preliminary estimate is
about 2 weeks. In the SPS draft schedule for 2007 the physics data taking
starts on May 26 and ends on November 11.