Minutes from target meeting held August 3 2007 in 888 and meetings July 24 - 27

These minutes are available also from:

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

a) Norihiro: on Friday July 20 heater on the LN2 trap flexible bellows off 
due to short circuit. Soon alarm from roots back pressure P3 exceeding 500 
mbar. The flow rate ok and pressure drop P3-P10 ok. Ramp up solenoid to check
polarization, which is zero due to high 1 K temperature. Start recovery
of 3He/4He mixture and isolate LN2 trap. Try circulation again with Tapio, but
now complete blockage of return line after 2 minutes. Needle valve NV2 is 
tested to be working. Continue recovery of 3He/4He mixture. Warm up LN2 trap.
Lot of gas inside. Big hole found from LN2 trap inlet tube. The mixture is
recovered with continuous pumping by Saturday 12:00. The leaking bellows
is fixed on Saturday morning by a welder. Pump LHe from 4He evaporator and 
evacuate 3He condensation line while keeping low pressure helium in the mixing
chamber. Restart pumping the 4He evaporator on Sunday morning 07:00. 
The evaporator empty on Monday morning 02:00. At 06:00 the TPR4 at 250 K and
TPR5 at 90 K. Pump inlet line from 04:00 to 06:00 with accessory pump.
NV2 open and NV3 closed. At 08:00 fill LN2 trap and start circulation with
10 mmol/s of 4He. Temperature around 1 K ok. Remove 4He between 14:00 and 
17:00. Recheck LN2 trap, no impurity in one hours circulation. Condense
big tanks O1-O4 on the roof of pump room. Immediate increase of P3 to 800 
mbar. On Tuesday morning 01:30 5 - 6 mmol/s flow. On Tuesday morning start 
condensing 3He tanks. Flow below 20 mmol/s. Blockage seems to be close
to the evaporator. System needs to be warmed up again. Start recovery of
3He/4He back to tanks. LN2 trap was leak tested to 10^-8 mbar l/s.

b) On Tuesday stop 4He evaporator pumps. Circulate warm 4He gas from the 
separator outlet to speed up the warming. Evacuate dilution cryostat from 
condensation line using leak detector and from pumping line with PR4 and PP4 
at the same time with NV2 and NV3 closed. Yuri: impure 4He gas that does not 
have any 3He should be thrown away. Possible contamination of H2 and O2. 

c) On Wednesday morning mixing chamber at 48 K, cavity at 47 K, evaporator 
73 K, precooler middle 150 K and bottom 110 K. At 02:00 small bumps in P10 
history probably due to removal of blocking nitrogen. 

d) On Thursday start circulation of 4He gas from the gas panel. Restart 
evaporator pumps. Check gas from tank O2 on the roof. Only 4He with 6 % water 
and 9 % of N2. Precool mixing chamber to 2 K Thursday - Friday night with
gas from tank O2.

e) On Friday morning start to condense 3He/4He mixture from the tanks. Condense
tanks O2, O1, O3 and O4 from the roots back side. Check the contamination and 
3He/4He ratio in the tanks #1 - #9 before condensing. #8 and #7 no 
contamination. N2 in tanks #6 16 %, #5 15 %, #4 7 %, #3 55 % and #2 10 %.
No contamination in #1 that was not used when the incident took place.
Condense the tanks #6, #5, #4 and #2 from the roots inlet side after stopping
the pumps. #3 is too dirty and is not used. At 19:00 restart roots. First 
polarization tests in the evening. On Saturday morning condense mixture from
tank #9. Low level of LHe in buffer dewar Friday - Saturday. Restart 
polarization Saturday noon.

f) Transverse data taking with dipole field from Sunday July 29 14:00 to 
Wednesday August 1 08:00. Repolarize from 11:00 to Thursday noon. -83.2 %, 
+81.9 % and -75.0 % polarizations reached. Yuri: set still heater to 10 V.
No polarization increase during the night with flow 54 mmol/s. In morning set
still heater to 12 V and the polarization starts to increase again. 

g) Yuri: superimpose SMC and COMPASS NH3 NMR signals to same plot with 
polarizations 60 % and 80 %. The signals lineshapes are identical and 
calculated correlation is 0.998 - 1.000. Jaakko: area ratio would give more
direct check to polarization error.