Studies of performance and field reproducibility of a precision 40kG superconducting dipole magnet Page: 1 of 5
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Proc. 1973 Particle Accelerator Conference BNL-17825
Son Francisco, Calif. March 5-7,1973
STUDIES OF PERFORMANCE AND FIELD REPRCD1CIBILITT OF A PRECISIO 40KG SUPEP.CONDUCTING
DIPOLE MAGNET
J. Allinger, G. Danby, B. Devito, S. Hsieh, J. Jackson, A. Prodell
Brookhaven Nat'l. Laboratory. Upton, L.I.,H.Y.
AbstractAn 8" bending magnet system for 30 GeV primary
protons from the Brookhaven AGS is to be installed in
the samer of 1973. This band requires operating two
magnet modules, each 6-ft. long, at an excitation up to
37kG. The cold bore I.D. is 3.375-in. A 20-in. long
full-scale cross section model has been extensively
tested. Multiple field components due to the magnet
circuit, produce field error -I x 10 c parts below
20kG out to the measurement radius at 827 of the radius
to the superconductor. The "good field" (.JzlO parts)
shrinks to a radius -50% of the radius to the super-
conductor by 40kG. Diamagnetic effects in the super-
conductor are completely negligible by Sko, with the
exception of the (r4, 59) multipole. This contributes
6.5 x 10'4 parts to the field at 82% of radius. End
effects are sufficiently small that for 6-ft. long
magnets little or no modifications of end contours are
required for even very exacting applications.
The magnet has operated to 45kG with no evidence
of significant training. The magnet has been thermally -
cycled several times, and the field aberrations allowed
by magnet design symmetries reproduce exactly from the
first to last measurement runs. At 19.1kG, all allowed
multipoles, i.e., 50,78,99,110, with 38 tuned to zero
agree to 1x10"* parts error over the duration of ex-
perimental measurements. However, ferromagnetic effects
due to martensitic transformations in the stainless
steel inner form on which the coils are wound have
grown with repeated thermal and magnetic cycling. These
effect particularly the remanence and the lower
harmonic components at the lower dipole field levels.
Model Magnet .
The 80 superconducting magnets are of the rec-
tangular aperture "window-frame" type with the iron
core surrounding a rectangular cross section dipole
coil package. The magnet cross section is shown in
Fig. 1. The aperture in the iron is approximately 4-in.
high by 6.25-in. wide. The overall dimensions are
14.875-in. high , by 17.125-in. wide. The iron
core, closely coupled around the coil, reduces the -
ampere turns required for magnetic fields below satu-
ration by a factor greater than 2. The images of the
coil in the iron give extended dipole sheets, pro-
ducing very uniform fields below 20kG. Above satu-
ration at the pole surfaces, the ampere turns require- t
ment, increases, growing by 21% at 40kG compared to
infinite permeability. The systematic aberrations due e
to saturation require an auxiliary correcting coil
which is approximately an aircore sextupole: The
excitation required of this correcting coil commences
at .20kG and grows linearly to several percent of the
dipole coil ampere turns by 40kG. The combination of
the two separate coils, the dipole and the correction,
permits precision fields at all levels, as well as
providing available sextupole "tuning" where desired.
The dipole coil is wound with 340 turns of a Nbri
composite with a rectangular cross section of 0.054-in.
by 0.113-in.
d
The conductor has 1.25 to 1 copper to sbpercon-
ductor ratio and contains 361 filaments of 3 mils
diameter, twisted one turn to the inch. Between each
single vertical layer of conductor are placed sheets
of anodized high purity aluminum, These shgets are
*Work performed under the auspices .
of the U.S. atomic Energy Commission
mASTERgrooved to provide vertical LHe channels over 50% of
the surface area. The high diffusivity and conduc-
tivity of the alaintmn provide enhanced thermal and
dynamic stability.
TABLE I
20-In. Model Magnet PerametersAperture, Diameter
Magnetic Field-Intensity
Ampere-turns, Dipole Coil
Ampere-turns, Sextupole Coil
Current, Dipole Coil
Current, Sextupole Coil
Current Density,
Dipole Coil Conductor
Current Density,
Sextupole Coil Conductor
Stored Energy
Inductance, Dipole Coil3.375 in.
40kG
408,000
18,000
1, 2OGA
300A2
3.05 x 104 A/cm
3.71 x 104 A/cm2
48kJ
55mHThe coil construction techniques and the test
assembly of the-20-in. model have been described in
more detail 1 -Fig. 2 shows the completed model.
The construction of the 20-in. model was used to
develop the techniques used in the construction of the
full sized magnets. Indeed these have proceeded with
no difficulties, in construction. Fig. 3 shows one of
the completed 6-ft. long magnets.
Magnet Performance
The 20-in..magnet is extremely stable. It can
be simply switched on to or off from its operating
field of 37kG. This results in current rise or decay
in seconds. The magnet has a solid core, and such
treatment result's-in very large losses. This fact
has been confirmed by a wattmeter measurement, as well
as by observed pressure fluctuations in the devar.
Nonetheless, the magnet does not go normal. Initial
tests were performed with large 120V SCR power supplies
with considerable ripple, and the magnet operated up
to 40kG. A remote switching failure in one of these
upplies resulted in the dipole current supply re-
maining on after a quench for an extended period.
The dear was boiled dry, which requires energy
dissipation 10 times that stored in the magnet. No
harm was done to the magnet.
After low voltage, highly filtered power supplies
were used, the magnet was excited to above 45kG. No
systematic attempt was made to raise this level by
repeated quenching.
In Fig. 4 is shown a normalized excitation func-
tion for the dipole field of the 20-in, magnet. Com-
puter results assuming Vitrenamel and M-36 permeability
lata are also sbwn. Vitrenamel sheet is a low carbon
teel which is close in composition to the plate used
in the magnet. It suffers some deterioration in
ermeability compared to thick plate, however, due to
he rolling process. In additiort iron at 4oK should
avg a slightly higher saturation induction than at
00 -. As a result, the fact that the model performs
etter than computations predict at 27.5kG and 30.6kG
DITRBUIO GJ Ta3 DQPN[i N iA~
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Allinger, J.; Danby, G.; DeVito, B.; Hsieh, S.; Jackson, J. & Prodell, A. Studies of performance and field reproducibility of a precision 40kG superconducting dipole magnet, article, January 1, 1973; Upton, New York. (https://digital.library.unt.edu/ark:/67531/metadc1022147/m1/1/: accessed March 18, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.