Minutes from target meeting held April 16 2010 in 892-2-009

These minutes are available also from:

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

a) Warm up LN2 trap in helium-3 circuit on Friday. About 0.2 bar gas 
(probably water) found. Leak test helium-3 roots cooling water circuit on 
Saturday. The leak detector connected through the LN2 trap to pump outlet
and helium flow into the water circuit after draining. No leaks detected.

b) Monday morning about 60 K reached in the mixing chamber and 56 K in the
helium-4 evaporator. Fill LN2 bath for target loading. Pressurize the
mixing chamber to atmospheric pressure with helium. Remove empty target
holder from mixing chamber and put it into the LN2 bath. Use plastic plug
to close the mixing chamber. Cool down the metallic plug in LN2 and replace
the plastic plug with it in the access tube. Fill the target cells with
ammonia and replace indium wire. Remove the metallic plug from the access tube
and insert the target holder into the mixing chamber. NMR coils, heaters
and thermometers working after loading. Leak test target holder vacuum and 
access tube volume. Pump out air and helium mixture from the mixing chamber
until 0.7 mbar pressure reached. Fill in helium gas 0.2 bar into the mixing 
chamber and start circulating the gas through the LN2 trap.

c) Tuesday morning start cooling down the dilution cryostat and filling the
magnet with LHe. Start the helium-4 pumps. Condense helium-4 into mixing 
chamber in the evening. Helium-3 roots stopped on Thursday morning due 
the cooling water flow switch. Readjust the switch threshold. Motor #8 "avant" 
cooling fan stopped. Replace #8 "avant" and #7 "derrier" fans on Thursday.

d) Start polarizing the ammonia on Thursday evening at 1.0 K temperature. 
Polarize first the central cell to positive polarization. About 50 times
increase in signal size observed. After switching off the microwaves the
NMR signal relaxation time about 20 - 25 min. Test also negative polarizations
for the up- and downstream cells. Yuri: one of the coils could be used
to measure nitrogen-14 NMR signal. Fine tuning of the microwaves needs to
be done at lower temperatures.

e) Kaori: no problem in the Yale card found at Bochum. The signal ok with
gain 1 but distorted with gain 207. Increase time out parameter to cure
the PXI communication lost error. Independent network between the PXI crate
and the NMR PC was discussed. Jaakko: check the Yale card in situ and buy
some spare components. 

f) Dilution cryostat PLC restart procedure was discussed. Norihiro: before
resetting the PLC the helium-3 roots cooling water interlock needs to be 
bypassed, isolation vacuum diffusion pump stopped and the helium-3 gate valve 
closed.