Minutes from weekly target meeting held 6th of November 2001 in 888

Schedule for the following week:

a) TE-calibration will continue until next Tuesday.

b) When TE-calibration is finished, we take EPR-line at high temperature 
about 1.4 K with the IMPATT diode microwave source from Bochum. This is 
expected to improve signal-to-noise ratio compared to the use of EIO-tubes. 

Results from last week:

c) The maximum polarization achieved with 100 ppm field homogeneity was about 
10 % less than what we got in normally trimmed SMC magnet.

d) Interesting results from relaxation time and superradiance measurements.
The relaxation time at zero field is about 7 - 8 minutes. During superradiance
measurement the speers were recorded for bolometry. Maser like behaviour 
was observed. SR resulted in spin ordering to 0-level. Yuri suggested the
use of such tensor polarized target for the transverse spin polarization 
measurements.

e) Technical run of the dilution cryostat showed that the dilution cryostat
is working well. Different still heatings 6 V, 8 V, 10 V and 15 V were tried.
Cooling power of 1 W could be seen at 0.5 K with 15 V still heating. At this
high circulation mode the minimum temperature was about 86 mK, while for
the lower still heatings the minimum temperature was about 50 mK. The minimum
mixing chamber temperature about 45 mK could be achieved with still heating
of 5 V. In single shot with still heating of 6 V, minimum temperature of
25 mK could be achieved.

f) During the recovery of the helium mixture about 10 500 m^3 of gas was put
to the tanks compared to the inventory of last March where 8 500 m^3 gas was
found. The big 1 m^3 tanks had to be pressurized up to 1.8 bar. This extra 
helium can be due to shielding gas that was added to the system when the roots
pumps were repaired or it could be initial precooling gas that was not 
removed before the mixture was condensed in. In the worst case there is an
internal leak from the evaporator volume to the dilution cryostat volume.
New gas inventory has to be done and leaks between evaporator and dilution
cryostat checked.

g) There was some brief discussion about the nonlinear corrections of NMR-
signals. According to Gerhard 30 % modulation depth leads to about 1.5 %
error in the polarization measurement. One of the Q-meter channels is very
noisy and the series resonance Q-value is about half compared to the other
ones. Signal sizes which are about half of the normal ones indicate smaller
filling factor and that the target cells are not completely filled with
6LiD.