15 April 1996
					G. Bunce


g-2 Ring News
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	The g-2 ring is being reassembled after removing the top iron to
lower the coil 2 mm and to prepare ports in the side of the cryostat to
accept a new radial stop design, and for windows to observe coil movement.
At this time, the iron is back in place, and the yoke is being leveled to
+/- .005".

	We have decided to use 8 radial stops based on an ANSYS study by
Chien Pai, and the analysis by Francis Farley in g-2 Note 255.  Chien studied
the 4-stop case, and qualitatively reproduced our observed coil movement.
(This is qualitative because friction is involved, and also we have not
resolved the expected radial force gradient yet.)  If we compare 8 and 4
stops with the ANSYS program, the radial shift of the coil for the same
force difference in azimuth is 3% for 8 stops vs. 4 stops.  Therefore, for
the same starting difference in radius, we expect to see the same movement
at 33x higher force for 8 stops.  We had our first movement just above half
field with 4 stops.  For 8 stops we would expect movement at 2.9x full field.
Francis studied the stability of a beam (mandrel) considering the force
gradients involved.  If the radial force gradient is chosen to match
observations with 4 stops (the coil appears to become unstable at 0.7 x full
field), for 8 stops the coil would be stable for any field.

	The stops will include springs.  The design by Lou Snydstrup and Jim
Cullen limits the stop motion radially in both directions.  Recall that the
stops are on the inside radius, mounted on the cryostat.  As the mandrel shrinks
when cooled, it first touches the stops at 85 K (as before).  Cooling to 5 K
compresses the springs 1 mm (before, the stops were rigid).  With the 8 stops
the force will be about 1000 lb.  The stop motion radially inward is limited to
3 mm.  As the coil is powered, the stop returns to its outer radial limit and
the coil is held there as long as its force doesn't exceed the preload of the
spring.  With this design, we reduce forces when cold, but maintain a fixed
position for the coil when powered.  The design includes the capability to
change springs and preload or to change to fixed stops after warming the ring
to 100 K.

	We will have 7 windows in the cryostat to monitor the coil position
as we cool and power.  We will be able to monitor radial, vertical, and
azimuthal motion.

	We are planning to use 8 stops (vs. 4) for the inner coils also, and
the stability of these coils is being studied.

	As already mentioned, Francis Farley has a g-2 note #255 on coil
stability, and Sergei Redin and Nick Ryskulov have written note #256 on radial
field measurements, including the measurements which detected the coil shifts.
Bill Morse is writing a summary of the measurements and analysis.

	The work on replacing the nitrogen heat exchanger in the refrigerator
cold box with an external one is underway and on schedule.

	We plan to begin the cool down May 1.