Minutes from target meeting held May 3 2007 in 888

These minutes are available also from:

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

a) Norihiro: hot spots were found from EIO tube microwave isolator. 
The isolator needs to be replaced. With modified wave guides 3 W was measured 
at the target platform using full 15 W power from the EIO tube. The power
controller reduces the power by 50 %. A collector resistor will be added
to the vacuum valve power supply to protect the EIO tube.

b) Kaori: Q-meter capacitors were retuned to get the circuit resonance to
the center of 600 kHz frequency window. 

c) The mixing chamber was filled with 4He and second thermal equilibrium 
calibration was started on Wednesday. Two temperatures 1.5 K and 1.0 K were
used. The magnet control for baseline taking needs to be done manually by
running a small script in the magnet control computer. 

Kaori: good fit to Curie law with typical errors 0.6 - 2.4 % and
4 - 6 % for coils #1 and #10. The error from back ground protons is assumed
to be small, but needs to be checked after the physics data taking.

d) Optimization of the 3He/4He mixture was discussed. In the initial 
condensation 3 tanks were not used to avoid too much 3He in the system. 
The mixing chamber cooled to 50 - 60 mK. Testing the helium level in still and
optimizing the 3He/4He mixture takes 1 - 2 days.

e) Magnet field rotation procedure from 2.5 T to 0.6 T dipole field was tested.
This includes the linear field gradient to avoid sudden loss of negative
proton polarization during ramping. Problem when going from -2.5 T to 0.6 T, 
all other procedures working. 1 T operation with linear field gradient has
not been implemented.

f) Fabrice: Gaussmeter shows that the dipole magnetic field is pointing down
inside the target cell. The NMR coils give central field of 0.632 T.