Magnetic properties of iron yoke laminations for SSC dipole magnets Page: 3 of 3
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4. INTERMEDIATE FIELD
In the intermediate field region the permeability
variei substantially across the yoke. The attributes
that affect the permeability are the chemistry which
determines Ms and the grain sise, etc. that affect Bc at
low field. The Frohlich-Kennelly relation was originally
intended to be a phenomenological expression describing
the approach to saturation where a(H) is generally chosen
to be a constant or a low order polynomial in In this
application however we are assuming that the entire H
range, which is four orders of magnitude, can be described
by the relation where a(H) is chosen so that the correct
B-H relation holds. Over this range a(H) varies by only
a factor of 5. Although a(H) itself is not a physical
quantity, it describes in some sense attributes related
to the permeability that are independent of Ms- In a
procedure similar to that which was used for Ms we
change the B-H curve by varying a(H) by a small amount
and using the Frohlich-Kennelly relation to reconstruct
the curve. Table 3 shows the results for a variation of
Aa = ±5 x 10~s. Although this chosen variation of Aa is
considered large it is not unrepresentative (unfortunately)
of what one can obtain. (We received a shipment of steel
which appeared to be “mechanically worked” to the extent
that the variation in a(H) was this large.)
Table 3: B0 verses I for curves corresponding to the
standard B-H curve and to those with a(H) increased or
decrease by 5 x 10-s.
Table 2: Ba verses I for curves corresponding to the
standard B-H curve and to those with Ms increased or
decrease by 78 Oe.
3. Data supplied by Armco Inc., Middletown, Ohio..
4. Data for this figure come from iron samples used for
ISABELLE, SSC prototypes, FNAL new maiming
project, LEP, and HERA. Published references are
• K. Sinram et al,77ie Influence of Fine
Blanking on the Magnetic Propertie* of
Soft Magnetic Iron, DESY (19S0).
• H. Laeger et al, Production of the Soft
Magnetic Steel Lamination* for the LEP
Dipole Magnet*, CERN LEP-MA/87-52
• Also we would like to thank Armco and
LTV for the use of their data.
“Work supported by the U.S. Department of Energy
Table 2 indicates that small effects of the onset of
the variation in saturation are present in the intermediate
region at 5000 amps. If we assume that the full allowable
tolerance in Ms is used at 8500 amps, then AMs at 5000
amps would represent only about 30% of the tolerance.
Since Ms and a are presumed uncorrelated, Aa can
take 95% of the allowable’ tolerance implying that Aa <
1.0 x 10~4 which we believe can be achieved.
1. M.J. Tannenbaum et al., Magnetic Propertie* of the
Iron Lamination* for CBA Magnet*, IEEE Transac-
tions on Nuclear Science 30-NS p3472 (1983), BNL
2. PE2D is a computer program for the 2D calcula-
tion of Poisson’s equation. PE2D Reference Manual,
VF088924, Vector Fields Ltd., Oxford, England..
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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/m1/3/: accessed March 21, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.