Magnetic properties of iron yoke laminations for SSC dipole magnets Page: 2 of 3
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RIRTIOM HI II
Table 1 give* B0 for a current iweep using the 0.7 (1.8)
Oe materials. Both the normal curve and the descending
curve are shown. (The normal curve is approximately
the average of the ascending and descending curves.) The
difference between the normal curve and the descending
curve gives AB0 = 1.0 (0.96) gauss for the Hc — 0.7 (1.8)
Oe. There is an additional contribution from the change
in permeablility that is associated to the change in Hc.
We see a change in B0 of 1.87 gauss for a change of Hc
of 1.1 Oe. As these affects are correlated we add there
contributions. Assuming that this difference represents a
variation in Bot the allowable variation in Hc is estimated
to be 1.1 Oe. which is quite large. Figure 2 shows the
RMS variation in He for steels used in and proposed to
be used in a number of different accelerator^ verses Hc.
The lower He steels are final annealed to various extents.
The higher He steels are not annealed. Some of the larger
AHc is supposedly due to working of the material to
make laminations. It is expected that the variation in Hc
will not be a problem and that requesting AJTC < 0.25
Oe should be attainable.
Table 1: B0 verses I normal and descending curves
corresponding to materials with He = 0.7 Oe and 1.8
Oe, respectively. The normal curve is the average of the
ascending and descending curves.
3 demonstrates this correlation. Hc is chosen such that
fs will be greater than 500 gauss/Oe for essentially all
samples. This procedure indicates that < Hc > should be
less than 1.8 Oe.
8 03 00
Figure 3: Permeability, /> verses Hc for different steels
used in existing and proposed accelerators.
He = 0.7
ffc = 0.7
Bc = 1.8
He = 1.8
3. OPERATING FIELD REQUIREMENTS
At high field the variation in field is due to variations
in the saturation magnetisation, Ms- To determine
the allowable variation in Ms, different B-H curves are
derived corresponding to a known deviation in Ms- These
B-H relations are obtained by using the Frohlich-Kennelly
COERCIVE FORCE I oersteds I
Figure 2t ABC verses Hc for different steels used in
existing and proposed accelerators.
The desired mean value of Be i* selected based on the
correlation between He and the permeability, ft. Figure
where a(H) is chosen to be a function of H so that it
corresponds to our standard B-H curve and Ms is allowed
to vary by a small known amount. Table 2 shows B0 for
various currents corresponding to the standard B-H curve
and to curves with Ms increased and decreased by 78 Oe.
At 6500 amps we find that with
a = 0.187 where a depends primarily on the geometry
of the yoke. The allowable tolerance permits a RMS
AMs = ±57 Oe.
Measuring AMs to sufficient accuracy to be useful
to monitor the production of the steel is not easy. As
Ms is primarily dependent on the chemistry of the s-
teel, monitoring the steel chemistry may be the practical
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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. (https://digital.library.unt.edu/ark:/67531/metadc1092938/m1/2/: accessed March 23, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.