Minutes from target meeting held May 7 2010 in 888

These minutes are available also from:

http://wwwcompass.cern.ch/compass/detector/target/Minutes/2010/

a) Start condensing helium-3/4 mixture on Monday morning. Dilution cryostat
partly blocked due to nitrogen in tank #3 from July 2007 accident. The other
tanks have already almost pure mixture. Warm up heat exchangers above helium-4
evaporator and try to restart circulation around midnight. Blockage still 
present. On Tuesday warm up the helium-4 evaporator to 22 K. Pump helium-3
condensation line from VH5 on top of the dilution cryostat with leak detector. 
Flush with warm helium gas from bottle with the LN2 trap connection valve
VC5. Nitrogen ice melts on Tuesday afternoon. Restart normal circulation with
small amount of helium-4 from the tanks.  

b) Restart helium-4 pumps on Wednesday morning. Condense helium-3/4 mixture
and finish at around 14:00. Test dilution cryostat with different still heater
voltages. Ruthenium oxide thermometer TTH5 indicates temperatures below its
lowest calibration point at 50 mK. Probably around 40 mK reached.

c) NMR system ready on Wednesday. First analysis of the empty and filled cell 
thermal equilibrium calibration done by Kaori. Ramp up the magnet to 2.5 T
on Wednesday evening. EIO microwave tubes warmed up during the day. The first
polarization values low due to error in the thermal equilibrium polarization
value. Deuteron value was used instead of proton. The magnet Danfysik current
transducer (DCCT) reported 646 A for the nominal field while in 2007 it was
651 A. Restart polarizing on Thursday morning. About 0.7 (70 %) reached in
10 hours. Small microwave leakage in the downstream stopper. At 18:00 switch 
off the microwaves and ramp down the magnet. Recover helium-3 back to 
the storage tanks and continue to circulate remaining 6 m^3 of helium-4 in 
the dilution cryostat.    

d) Norihiro: pump room door should be kept closed for the air conditioning.
LN2 dewars can only be filled in exceptional cases. Horizontal screen heating
cable may have a short circuit. Jaakko: the circuit breakers on the Saleve
side open in the magnetic field. Vacuum gauge PT48B under the platform on
the Jura side needs to be connected to safe power supply line. Loss of this
reading can result to fast discharge in the magnet.

e) Fabrice: new network to the magnet PC and VME crate. The software updated
by Jean-Francois. Connection to the NMR PC works now.