MAGNETIC DESIGN OF A HIGH GRADIENT QUADRUPOLE FOR THE LHC LOW B INSERTIONS. Page: 1 of 3
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BNL-69121
MAGNETIC DESIGN OF A HIGH GRADIENT QUADRUPOLE
FOR THE LHC LOW-0 INSERTIONS
G. Sabbi, S.A. Gourlay, J. Kerby, M.J. Lamm, P.J. Limon, F. Nobrega, I. Novitski,
J.B. Strait, A.V. Zlobin, FNAL1, S. Caspi, R. Scanlan, LBNL1, A. Ghosh, R. Gupta, BNL'Abstract
Fermilab, Lawrence Berkeley National Laboratory and
Brookhaven National Laboratory have formed a consor-
tium to provide components for the Large Hadron Collider
(LHC) to be built at CERN. The U.S. contribution includes
half of the high gradient quadrupoles (HGQ) for the inner
focusing triplets. In this paper a description of the HGQ
magnetic design is given, including short sample limit for
field gradient, sources and expected values of systematic
and random field errors, and possible strategies for field
quality correction.
1 INTRODUCTION
In order to achieve a luminosity in excess of 104 cm2s1
at the LHC, special high gradient quadrupoles are required
for the final focusing triplets [1]. These magnets must pro-
vide a field gradient of 235 T/m over a 70 mm bore, with a
sufficient margin in order to withstand the heavy heat load
due to secondary particles from beam-beam collisions. At
the same time, due to large and rapidly varying values of
the ,3-function, a high field quality is required. To meet
these severe constraints, a design based on a two-layer coil
geometry has been proposed [2]. The magnet uses SSC-
type NbTi superconducting strands and operates in super-
fluid helium. The first short model of this design is being
fabricated and will be tested this fall. In this paper, the mag-
netic design for the HGQ straight section is discussed.
2 MAGNET DESIGN
The HGQ design is based on four two-layer coils connected
in series, surrounded by collar and yoke laminations. A
thick-wall stainless steel beam tube also serves as an inter-
nal beam absorber. With respect to the last status report [2],
the coil prestress is now entirely provided by the collars.
For this purpose the collar material has been changed from
aluminum to stainless steel, and the collar width at the mid-
plane has been increased from 20 to 25 mm. The yoke inner
radius at the midplane is now 92.56 mm while the outer ra-
dius remains unchanged at 200 mm. The yoke lamination
features four round holes for the Hell heat exchanger and
four rectangular holes for electrical connections, as well as
special cutouts for magnet fabrication. In the pole regions,
eight rectangular gaps between collars and yoke house tun-
ing shims for field quality adjustment [3]. The resulting
HGQ cross section is shown in Figure 1.
The cables for the magnet models are made of SSC NbTi
strands with a critical current density of 2.75 kA/mm2 at 5 T
ISupported by the U.S. Department of Energy.Figure 1: HGQ cross-section
and 4.2 K. The SSC strands will eventually be replaced with
improved ones that are now under development, with the
goal of increasing the critical current density to 3.4 kA/mm2
at 5 T and 4.2 K. Table 1 shows the HGQ short sample limits
at 1.9 K operating temperature, calculated for both existing
and new strands.
Table 1: Short sample limits.
Jc(5T, 4.2K) G,., I,, Bm12er B m"Ner
kA/mm2 T/m kA T T
2.75 253.8 14.2 9.9 8.2
3.4 270.2 15.2 10.4 8.8
The operating current is 0.8 kA at injection and 13.1 kA
at nominal gradient. At nominal current, the magnet will
operate at 93% along the load line with the SSC conductor
and at 87% with the improved one.
3 FIELD QUALITY ANALYSIS
The design low-order harmonics for the HGQ central
field, resulting from the cross-section optimization with
a circular yoke of infinite permeability, are b6=-2-10-3,
blo=-1.3.10-5. All other normal and skew harmonics with
n< 14 are zero. The harmonics here and below are given in
units of 10-4 of the main quadrupole field at 1 cm reference
radius.
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Sabbi, G.; Gourlay, S. A.; Kerby, J.; Lamm, M. J.; Limon, P. J.; Nobrega, F. et al. MAGNETIC DESIGN OF A HIGH GRADIENT QUADRUPOLE FOR THE LHC LOW B INSERTIONS., article, May 12, 1997; Upton, New York. (https://digital.library.unt.edu/ark:/67531/metadc733366/m1/1/: accessed April 19, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.