Minutes from target meeting held January 9 2015 in 892-1-D20

These minutes are available also from:

http://wwwcompass.cern.ch/compass/detector/target/Minutes/2015/

a) On Tuesday December 2 2014 condense helium-4 rich mixture after removal of
helium-4. Ramp up magnet to nominal field on Wednesday. First NMR signals 
from unpolarized ammonia could be seen. Test polarization build up at around
1 K temperature.

On Thursday condense same helium-3/4 mixture that was used in run 2011. On 
Friday test polarization build up at about 110 mK. Remove helium-3 from mixing 
chamber for the weekend. 

b) After beam time on Monday December 8 exchange horizontal and vertical
screen flow controllers. Normal horizontal screen temperature 25 K reached.
Start to re-condense helium-3/4 mixture to mixing chamber.

On Tuesday run dilution cryostat with nominal mixture. High back pressure
makes operation difficult.

Pump out helium-3/4 mixture from Tuesday to Wednesday.

c) On Thursday December 11 analyze gas composition after helium-3 roots pumps. 
The mixing chamber was at 1 K at this time and pressure below 10 mbar. 
Repeat the same analysis on Friday afternoon when mixing chamber was warmed 
to 55 K. The helium-3 pumping line pressure was at 105 mbar due to evaporation
of gas from mixing chamber. Analyze gas sample again on Tuesday afternoon
after unloading of the target material. This is the gas that was circulating
just before opening of the access tube.

mass   gas candidate     11 Dec[%]   12 Dec[%]  16 Dec[%]
2      H2                 6           0.5        0
3      helium-3           0           0          0
4      helium-4          68          97.5       99.5
17     NH3                2           0          0
18     H2O               12           0.8        0
28     N2                11           0.5        0.5
32     O2                 0           0          0

d) On Tuesday December 16 2014 unload polarizable solid ammonia target. The
material temperature about 74 K just before removal of target holder. 
The unloaded material was stored in LN2 dewars.

Close access tube with plastic plug that has a small air leak. Pump out gas
from mixing chamber and fill in 0.8 bar helium gas. On Thursday the access
tube thermocouple shows a temperature of 182 K.

e) On Wednesday December 17 close main water valves  behind barracks. Purge
helium-3 and helium-4 pump cooling water circuits and valve manifold. Leave 
purge valves on pumps and manifold open.  

f) On Wednesday December 17 warm up LN2 trap in helium-3 circuit. Stop
automatic refilling of LN2 trap. 

g) On Wednesday January 7 2015 access tube at 242 K. Pump out gas from mixing
chamber and fill in 0.9 bar of helium gas.

On Friday afternoon open access tube and replace plastic target plug with
metallic one. The metallic plug is leak tight and prevents further air
humidity from entering into the access tube and mixing chamber volumes. 
Pump out gas from mixing chamber and fill in 0.8 bar of helium.