Minutes from target meeting held June 19 2015 in 892-1-B09

These minutes are available also from:

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

a) Start removing helium-3 rich mixture on Sunday afternoon. Pump out the
helium-4 rich mixture over the night. On Monday prepare the helium-3 vapor
pressure thermometer. Set dilution cryostat over pressure valves to open
configuration. Start to condense helium-4 from gas panel.

b) On Tuesday morning mixing chamber filled with superfluid helium-4. Ramp
up the magnet to 2.5 T field with negative solenoid current. Six of the
helium-3 roots pumps were running and the mixing chamber was at about 1.4 K.

For certain time periods high noise in the NMR signals was observed. Improve
grounding of the NMR rack under the target platform. Change position of
frequency synthesizer and Q-meter power supply to allow better passive air 
cooling. These devices were fixed more carefully to the rack. The
noise condition became better after 20:00 on Tuesday evening.

c) On Wednesday morning start one more roots pump to reach lower temperature.
All the roots pumps were switched on from midnight to reach temperature
around 1 K. 

d) On Thursday evening start to pump out helium-4 from mixing chamber.
Use mixing chamber heater on Friday afternoon to get out the helium-4.
The mixing chamber warmed to 27 K to remove possible blockage in the
connecting capillary of the helium-3 vapor pressure thermometer.

Change over pressure valves to closed circulation configuration. Start seven
roots pumps. Use small amount of gas from tank O1 to cool down from 27 K to 
below 2 K. During this operation at the start of the Joule-Thomson cooling
oscillations in dilution cryostat pressures are observed and high helium-4
flow from the evaporator is used. After the stable temperature in the mixing
chamber below 2 K was reached open tanks O1 - O4 and start to condense slowly
from VC11 in the gas panel.
 
e) Problem in reading resistive thermometers from one of the AVS47 bridges.
Open AVS47-IB box and examine connections with multimeter. Check the
solderings on the PCB. Check the correct power supply voltage 5.0 V. Check 
presence data in GPIB lines DIO1 - DIO8. DIO1 did not show any data flow.
Finally problem found from bad GPIB connector external of the AVS47-IB box.  

f) Fabrice: update magnet power supply software. 

Change LHe transfer valve CV0004 set point in the magnet from 85 % to 90 %. 
This should remove the occasional CV0004 open too long time alarm and
allow more efficient magnet filling.

g) Fabrice: The pump room air conditioning unit replacement is planned for 
end of November.