From MORSE@bnlarm.bnl.govThu May 23 17:22:26 1996
Date: Wed, 07 Feb 1996 13:18:13 -0500 (EST)
From: MORSE@bnlarm.bnl.gov
To: earle@buphy.bu.edu, monich@buphyc.bu.edu, varner@buphyc.bu.edu,
    OUYANG@buphyc.bu.edu, CAREY@buphyc.bu.edu, krienen@BNLDAG.AGS.BNL.GOV,
    messier@buphy.bu.edu, miller@buphyc.bu.edu, roberts@buphyc.bu.edu,
    worstell@buphyc.bu.edu
Cc: c.disco@wmw.utwente.nl, koniczny@princeton.edu,
    lowenstein@BNLDAG.AGS.BNL.GOV, tkirk@bnl.gov, yamin@BNLDAG.AGS.BNL.GOV,
    roser@BNLDAG.AGS.BNL.GOV, lessard@BNLDAG.AGS.BNL.GOV, barton1@bnl.gov,
    geller@bnlux1.bnl.gov
Subject: Magnet News
Resent-From: MORSE@bnlajc.bnl.gov
Resent-Date: Wed, 7 Feb 1996 13:19:17 -0500 (EST)
Resent-To: woodle@ad1.ags.bnl.gov, YIM@INP.NSK.SU, dz@budoe.bu.edu

               Magnet News - 7-Feb-96  - Bill Morse.

     Let me review where we are in the magnet testing program. We 
went to half-field (2450A) on January 1, 1996. There was one
surprise previously. Namely, that the wedges moved. We now understand 
that this is due to the mu of the iron changing from 10^4 to 300 
from low to full-field. The wedges give a uniform field at 5200A.
Iron moves in a non-uniform field, which we get on the way up to
full-field. A simple fix was installed, which worked amazingly well.
We are now working on an even better fix, which has been on the
back-burner for a while. Extensive magnetic measurements were made at
half-field. The time stability of the magnet is impressive: precision
magnetic measurements can be made within half an hour of ramping up.
Of course, without time stability we don't have an experiment. The
azimuthal field uniformity was about what we expected. However, some of the
changes in field going from one pole piece to another exceed our 
tolerance. This is correlated with the pole gap. We now know the
step must be less than .001". This was our goal in constructing the
magnet, however, some steps are larger. We extracted the energy and
remapped the field. The quench-back data agrees with our quench
analysis. The "umbrella" effect due to eddy currents in the iron was
+-10ppm. This is within our tolerances. 

     The cryogenics, magnet power supply/ quench protection, vacuum,
and field measurement systems have generally worked well. An
important part of this process is getting operating experience with
these big systems. On January 27, 1996 we were ready to go to
full-field. However, at 3650A, we extracted the energy because the
outer upper - lower coil voltage difference exceeded 50mV. We also
heard the outer coil move. The good news is this did not cause the
magnet to quench. The bad news is: it isn't supposed to move enough
to cause a 50mV coil voltage difference. Serge and Nick have built a
precision Hall probe device to measure the radial magnetic field in
the muon storage region. They used this device to measure the radial
field at many locations around the outer coil. The design of the
outer coil was that center be 0.5 - 1mm below the centerline, so the
vertical magnetic force is in the same direction as gravity. Their
measurements show the coil is about 1.5mm above the centerline. This
gives an upward magnetic force, which changes the forces on the
straps and radial stops from what we considered during the design. We
calculate that the upward magnetic force is about equal to half the
coil weight at 3600A for a 1.5mm displacement above the centerline.
We have analysed the different coil movements possible due to the new
force on the straps. We have come to the conclusion that these forces
are within safe tolerances. We have analyzed our quench-back data to
see how high the energy extraction trigger can be. We have concluded
that it can be safely set to 0.5V. Our immediate problem is that
since we lost lab power last Friday for 30 minutes, we have not been
able to make liquid Helium. We are doing tests now to understand the
problem. Once we understand the origin of this problem, and once we
make liquid Helium, we will resume our tests with the energy
extraction system coil voltage difference trigger set to 0.5V. We can
readjust the height of the outer coil so it is below the centerline.
However, the coil must be warm to do this, and we would have to take
off the top yoke sections. This would take about two months, including
warm-up and cool-down.