Magnetic design of large-bore superconducting quadrupoles for the AHF. Page: 2 of 5
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Magnetic Design of Large-Bore
Superconducting Quadrupoles for the AHF
Nikolai Andreev, Vladimir S. Kashikhin, Member, IEEE, Vadim V.Kashikhin, Peter J. Limon,
John Tompkins, Fermilab
Andrew Jason, Peter Walstrom, LANL
Abstract- The Advanced Hydrotest Facility (AHF), under study
by LANL, utilizes large-bore superconducting quadrupole
magnets to image protons for radiography of fast events. In this
concept, 50-GeV proton bunches pass through a thick object and
are imaged by a lens system that analyzes the scattered beam to
determine object details. Twelve simultaneous views of the object
are obtained using multiple beam lines. The lens system uses two
types of quadrupoles: a large bore (48-cm beam aperture) for
wide field of view imaging and a smaller bore (23 cm aperture)
for higher resolution images. The gradients of the magnets are
10.14 T/m and 18.58 T/m with magnetic lengths of 4.3 m and 3.0
m, respectively. The magnets are sufficiently novel to present a
design challenge. Evaluation and comparisons were made for
various types of magnet design: shell and racetrack coils, cold and
warm iron, as well as an active superconducting screen. Nb3Sn
cable was also considered as an alternative to avoid quenching
under high beam- scattering conditions. The superconducting
shield concept eliminates the iron core and greatly lessens
the cryogenic energy needed for cool down. Several options are
discussed and comparisons are made.
Index Terms- Superconducting Magnets, Quadrupole,Large
Bore, AHF, Magnetic Design.
T HE Advanced Hydrotest Facility (AHF) , under study by
LANL, utilizes large-bore superconducting quadrupole
magnets to image protons for radiography of fast events .
The magnetic optics of this facility is based on large bore
quadrupole magnets. The large quantity ( ~ 84 ) and large
length 3 m - 4 m of this magnet are the reasons careful
optimization of all steps for magnet design.
One of the challenges in this design is obtaining a high
quality ( 10~4) quadrupole (magnetic) field in 100 % aperture.
This follows from the beam optics aberration analysis .
Another challenge for the magnet design is a severe space
limitation in magnet width. Because quadrupoles will be
installed very close to each other, no fringing fields will be
allowed. The limited space for return flux in the median plane
directs the design to a "Figure-8" type quadrupole.
Manuscript received August 4, 2002.
N.Andreev, V.S.Kashikhin, V.V.Kashikhin, P.J.Lirnon, J.Tompkins with
FERMILAB, Batavia, IL 60510, MS 316, USA. E-mail: firstname.lastname@example.org,
A.Jason, P.Walstrom with LANL.
One of the options to reduce magnet weight and eliminate
fringing fields is to use an active shielding winding. The lower
magnet weight and dimensions compensate the larger quantity
The rather attractive option is to have a cold iron core which
help to reduce the quantity of superconductor but iron
saturation effects should be carefully investigated.
The large magnetic forces of -300 t/m can cause problems
with mechanical stability. The racetrack type coils can
accommodate these forces easier than shell type coils but have
Because of rather high magnetic field 6 T - 8 T in the area
of superconducting coils the proper choice of superconductor
NbTi or Nb3Sn also should be investigated.
II. BASIC DESIGN PARAMETERS
The project is oriented towards lowering overall magnet
system cost, achieving a high field quality, and using existing
superconducting magnet manufacturing technologies.
There are two types of superconducting quadrupoles to
work with different image resolution.
Main Quadrupole Parameters
Parameter Large Small
Nominal quadrupole gradient, T/m 10.14 18.58
Maximum quadrupole gradient, T/m 13.18 24.15
Aperture diameter, mm 482.6 228.6
Magnetic length, mn 4.3 3.0
Magnetic field nonlinearity, % S 0.01 s 0.01
at the reference radius, mm 241.3 114.3
Total quadrupoles width, m 1.92
LHe Cooling, K 4.2 4.2
The total width of both quadrupoles should not exceed
1.92m in most narrow space between magnets. The width of
each quadrupole can be estimated taking into account the same
magnetic resistance for the return flux and relations between
winding radiuses and gradients as :
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Jason, A. J. (Andrew J.); Walstrom, P. L. (Peter L.); Andreev, N. (Nikolaĭ); Kashikhin, V. S. (Vladimir S.); Limon, P. J. (Peter J.); Kashikhin, V. V. (Vadim V.) et al. Magnetic design of large-bore superconducting quadrupoles for the AHF., article, January 1, 2002; United States. (https://digital.library.unt.edu/ark:/67531/metadc930825/m1/2/: accessed March 25, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.