Minutes from target meeting held on 4th of September 2002 in 892-1-D20

a) Kaori presented the preliminary polarisation data from the 80 days
of run 2002 so far. Maximum polarisations of +55 % and -45 % were achieved.
The polarisation was lost 2 times in this period. Kaori presented also
sample of polarisation data, where the negative field TE-calibration was
used for the negative field polarisation measurement and positive 
TE-calibration data for the positive field direction. The spread between
different coils after field rotation was significantly reduced.

b) Gerhard R. talked about idea to check the polarisation with only one coil
at a time by terminating the others to 50 ohms. When this has been tested
no dependence of the signal area on the microwave power has been seen.
Then the TE-calibration could be done one coil after the other. The NMR
system has been tuned now only to the positive field. Gerhard M. commented 
that there could be some effect between the different
coils through common coupling to the target material. 

c) Jaakko showed that the NMR-signals seem to fit well to the microscopic
theory of dipole-dipole interaction in positive field. After field rotation 
unsymmetric "dispersive" lineshape is observed in upstream coils. This can 
be partially corrected using Krames-Kroniger relation and by shifting the 
phase, but the resulting signal does not fit as well to the memory function
as before the field rotation in positive field. 

d) Yuri said that the most likely reason for the different behaviour between
positive and negative field directions is due to elliptically polarised
RF-excitation. This can be checked during the next MD by using only one coil
and terminating the others to 50 ohms. Yuri said that not all the necessary
measurement instruments for testing the NMR coils and their mutual coupling
are available. In the SMC experiment a vector voltmeter was used for this 
purpose.

e) Werner said that the NMR-problem can be fixed for next year. Gerhard M.
asked whether the spread between the polarisations measured by different
coils is understood. Stefan said that the spread in polarisation measured 
by different coils seems to be a real physical phenomena. It can not
be attributed to different radiation doses of different patches, since
the same behaviour was observed already last year and the material was
remixed during the material loading this year. Gerhard M. said that 
if there is a good idea to improve the design of the cavity to get more
uniform and higher polarisation, this could be done for the next year.
Werner said that testing such modifications is time consuming in the
big system of COMPASS. 

f) Werner said that about 100 ccm more material was filled this year compared
to last year. The material needs to be weighted after the run to determine
the filling factor. 

g) Jaakko said that coil #6 inside the target material is showing a little
lower polarisation compared to the outside coils. The reason for this could
be screening of the microwaves by the target material. Yuri said that there
could be small microwave leakage from upstream which could explain the lower
polarisation. Stefan said that the next coils #7 and #8 show high polarisation
and microwave leakage should show low polarisation near the stopper which
increases when moving away from stopper. Gerhard M. said that the microwave
leakage should be quantified during the technical run. Yuri said that the thin
one wall stopper foil is never exactly straight and is probably concave
on one side and convex on the opposite side resulting in different microwave
distribution. Yuri said that typical microwave power needed is about
0.1 mW/ccm for 6LiD. Gerhard M. asked why the different coils show different
asymptotic behaviour during polarisation. 
 
h) Jaakko presented the summary of the technical problems in run 2002.
Solved problems were: leak to TH iso vacuum, shorted SMA connectors inside
TH iso vacuum, 6LiD leaking out from target cell, frozen target plug inside
access tube and ice in dilution cryostat, and too small current capacity
of pump room fuses. Partially solved problem is the connection between
the NMR cables/coils and thermometers, which caused noisy NMR signals, 
dependence on microwave power and on field direction. Remaining problems
are magnet LHe vessel leak, automatic LN2 trap filling, roots cooling
water pressure drop, magnet PSU demineralised cooling water drop, rare
problems with trim PSUs and "tiroir inversion",  broken EIO tube, 
complaints about impure returning gHe and liquefier problems, one beam
interlock failure, one field rotation failure, and dipole PSU current
lead interlock failure (was solved later). Yuri proposed to use thermal
protection for the solenoid and dipole supply transistor banks instead
of cooling water interlock.

i) The possibility to recover from solenoid PSU slow discharge was discussed
after Gerhard M. asked about this point. Gerhard R. said that in the SMC
this was done by setting the current to a lower value, which caused the
ramp down to stop at that value.

j) The technical run after the beam time ending 18th of September at 10:00
was discussed. The most important part is the TE-calibration of the deuterium
NMR-signals. Thus the TE-calibration should be done first. Stefan wanted
to check how the EPR-lines from upstream and downstream target cells shift
from the centre at different spin polarisation values. For this the 
polarisation can be build step by step in two days. The polarisation
build up is done with IMPATT diode microwave source, to check how fast
with their limited power the polarisation can be build up. Gerhard R. wanted
to check if the proton spin temperature follows the general spin temperature
of the other nuclei. This could be done by re-tuning the small coil #6
inside the target material to the proton frequency at 2.5 T. Going from
dilution cryostat mode to 4He mode is expected to take about 1 day.
Norihiro wanted to check the cooling power of the dilution cryostat. Jaakko
said that this is a good idea, since there can be ice to deteriorate the
performance of sintered heat exchangers. At least 2 weeks are needed
for the technical run.

k) The situation of the microwave EIO tubes was discussed. Presently there
are two old vacuum valve PSUs and one old working EIO tube. In addition
there is the "SMC spare" EIO tube and 2 new tubes from Nagoya. One new
semiconductor PSU without FM possibility is also available. Yuri and Stefan
checked the specifications of the new and the spare EIO tubes. The cathode
voltage needed by it is 6 kV and the old PSU can only provide 5.2 kV.
Thus the old PSU is not directly compatible with the tube.

l) The 300 mW IMPATT diode should be enough for polarising especially if
the microwave source is placed close to the target to avoid losses in the
wave guides. Even 500 mW IMPATT diodes are available from USA, where their
price is about 10 kEuro while the Russian diodes with lower power are
typically 2500 Euro. Gerhard M. reminded that the EIO tubes will 
be needed for polarisation of ammonia. Possibility to repair the broken
EIO tube at Varian was discussed. Werner said that the price is probably
20 % less than a completely new one. The second semiconductor EIO tube
with FM possibility would cost about 47k$. One possibility is to do 
the modifications to the PSU is at Bochum workshop.  

m) After the run several parts of the target need maintenance. Saclay will 
take the responsibility of the SMC magnet for 2003 and make the necessary
work on the magnet PSUs. Yuri said that the roots pump #5 in 3He pump system
has low oil level and is noisy. Jaakko said that the noise is probably
from the cooling fan and we need to buy spare fans. The oil for this system
needs to be changed. In addition to oil change for the 4He rotary and
roots also the oil filter has to be changed. The oil change should include 
also leak testing of the pump system.

n) The draft SPS schedule was discussed briefly. The real physics data taking
will start 26th of May and the area will close on 19th. Preliminary date
for target loading would be after Easter around 20th of April.

o) Possible spare 6LiD material production was discussed. The Lithium
and Deuterium are available, but some of the equipment (furnace etc) are 
missing. One person would be needed permanently at Bochum to do the necessary
work, which is expected to take about 6 months. The irradiation cryostat
should also be updated, but for the spear material production the old one
could be used as well. Stefan pointed out that the 6LiD is very sensitive
to humidity or water, which produces white LiHO on the material surface.
This surface impurity could also explain the difference between the negative
and positive polarisation values.

p) Fabrice presented the shift load of target members permanently at CERN
and those outside. Typical shiftload between weeks 20 and 40 has been
51 for the members at CERN (by scaling week coordination to correspond to
6 shifts) and 6.8 for those outside. Gerhard M. said that there has to
be better planning for the availability of the experts in the beginning of the
run.

q) Gerhard M. reported briefly about progress in the work on the Oxford
magnet. The plan is to test the magnet at CERN in November 2003 and to
have it ready for 2004 run. Gerhard M. said that help is welcome to
the magnet preparation process.