Magnetic properties of iron yoke laminations for SSC dipole magnets Page: 1 of 3

rresentea at
1991 Particle Accelerator Conference
Sheraton Palace Hotel, San Francisco, California
May 6-9, 1991
DE91 014783
S.A. Kahn and G.H. Morgan
J < i
Accelerator Development Department
Brookh&ven National Laboratory, Upton, NY 11973
JUL 0 8 ISO?
We examine the magnetic propcrtie* for the iron
used in. the SSC yoke laminations so that the accelerator
tolerances can be met. The accelerator requirement* for
field quality specify a tolerance on the variation in the
central field. At machine injection the variation in field
is attribnted to eoercivity, Hc. Requiremeida on the
magnitude and the variation of Bc are presented. At the
8.65 tesla operating field the variation in the saturation
magnetisation dominates the magnetic tolerance for the
A high degree of central field uniformity is required
for the SSC main ring dipoles. This requirement is
specified by a RMS tolerance in < 0.001. It
is assumed that a tolerance half of tlis value can be
safely assigned to variations in the iron properties of the
yoke. Since iron properties are independent of magnet
construction errors, these tolerances can be added in
quadrature. Tolerances for Fourier harmonics higher than
the fundamental, JBo, are not significantly influenced by
variations in iron properties.
In this study iron properties are examined at loir
field corresponding to beam injection, at medium fields
with rapid changes in permeability, and at the high
operating fields. At low field the variation is expected to
be dominated by Hc or effects correlated to Hc such as
the low field permeability. Low field properties tend to
be related to grain sise, work hardening, etc. The final
processing that is done to the steel has a large effect on
Bc as it also has on other properties such as the yield
strength of the material. In this report we only conrider
the magnetic properties of the yoke material, however
mechanical properties are considered so as not to make
inappropriate specifications. The magnetic effects at high
field are dominated by the iron saturation. The iron
saturation is governed by the chemistry of the iron. In
this report we describe the calculations that hsve been
done to establish the desired iron properties for the SSC
main ring dipole magnets. A similar type of analysis was
performed on the yoke steel for ISABELLE magnets.1
aperture from, the remnant field in the iron we can apply
Ampere’s law to a closed path through the aperture and
around the yoke. Figure 1 shows the flux lines for the 5
cm dipole magnet at injection field. Applying Ampere’s
law assuming that there is no current in the magnet gives:
Bo X lf.r + Biton X lire. = 0
The mean ratio of ^ can be determined by taking the
flux average of the lengths. This ratio is
/£-):* 1.71
' ‘tv '
We would expect the variation, AB, in the aperture
region due to variations in Bt to be
where dll, is allowed to be 3.3 gauss by the previously
mentioned tolerance. This provides a rather achievable
requirement that ABe < 1.9 Oe.
Hi -
12.! *
11.0 1S.0 l*.0
1.0 t.O S.0
10.0 12.0
Figure 1: 5 cm SSC dipole with flux plot corresponding
to injection field.
At machine injection energy, the main ring dipole A more complete analysis of the low field behavior
magnets see a field of 0.68 tesla. At injection current of this magnet was performed using the finite dement
the variation in field is dependent on remnant fields program PE2D* with normal B-H tables corresponding to
from previous excitations and deviations in the low field Bt = 0.7 Oe and 1.8 Oe.3 To simulate the hysteresis effect
permeability of the steel. Both of these effects axe on these curves Bc is subtracted (added) to each of these
dependent on Be. To estimate the sise of the field in the curves corresponding to the descending (ascending) carve.

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Kahn, S.A. & Morgan, G.H. Magnetic properties of iron yoke laminations for SSC dipole magnets, article, January 1, 1991; Upton, New York. ( accessed April 22, 2019), University of North Texas Libraries, Digital Library,; crediting UNT Libraries Government Documents Department.

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