LBL program of 1 meter long, 50 mm diameter bore, dipoles with fields greater than 8 tesla Page: 3 of 7
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LBL PROGRAM ON i METER LONG* 50 MM DIAMETER BORE. DIPOLES WITH
FIELDS GREATER THAN 8 TESLA*
Vi. V. Hassenzahl, W. Gilbert, C. Taylor, and R. Meuser
Lawrence Berkeley Laboratory
University of California
Berkeley, California 94720
Abstract
Model dipole superconducting magnets with central
fields above 8 tesla are being developed for future
mult^-TeV colliding beam accelerators. The first
three models are I meter long, have nominal 50 nn
dianeter cold bores* and utilize Nb-Ti superconductor
operating in He II at 1.8 K. None of the three
models had an Iron flux-return yoke. The maxima*
central fields achieved are 8.0, 8.6, and 9.1 tesla
— all short-sample performance at 1,8 K for the
conductors used. At 4.3 K the maximum central fields
are from 1.5 to 2.0 tesla lower. In one design, the
superconductor is arranged in four concentric
cylindrical layers, sometimes called a four-shell
geometry. With higher current density Nb-Ti we
expect this design to reach 10 tesla central field
and a two layer design to reach 8 tesla. The other
design uses 8 flat pancakes with upturned ends.
Improved Nb-Ti should also allow this design to reach
10 tesla central field. This geometry is being used
for our WnSn wind-and-react dipole to be operated
1n He I at 4.3 K.
Program Suamary
Existing high-energy accelerators have reached a
size that appears to be a limit of machines using
conventional magnets, and the first accelerator using
superconducting magnets is now in the process of
being commissioned and should soon be operational.
Because they allow both size and operating costs to
be reduced superconducting magnets appear to be the
clear choice for future high-energy synchrotron
accelerators, unless same other acceleration tech-
nology is developed.
operation. To reduce cost we have used 58.5 mm for
our recent magnet development program and see no fun-
damental limitation down to about 40 mm. Special
consideration must be given to the ends of small mag-
nets due to difficulty in bending conductors around
the snail radius at the pole.
T:ie development of magnets that operate 1n the 8
to 10 T range is an extension of the development of
lbwer-vr1eld magnets. The local body forces are a
product of current density and field. At higher
fields •'he current density in the superconductor
decreases and with no other changes this product
would raeain roughly constant. At high fields,
however, Increasing the current density in the wind-
ing is very effective in terms of the quantity of
superconductor required. This 1s accar.plIshed by
developing superconductors with increased critical
current capability and by ••educing the copper-to-
superconductor ratio. The resulting pressure at the
mldplane of the raiding, even for 50 an bore coils,
can approach 136 H>a (20,000 psi), which is about a
factor of two greater than the pressure in the Fer-
milab doubler colls.
We use two commercial superconductors: an alloy
of niobium and titaniun (Nb-Ti), and a compound of
niobium and tin (NbgSn), for accelerator dipoles.
The approximate field limits for these materials are
shown in Table I.
Table I
Kaxlmu* Design Field for Superconducting
Accelerator Dipoles
The optimijn field and bore of the superconducting
magnets destined for future machines are not so
certain. The choice of these parameters will be
based un tradeoffs among many factors. The lower the
field, the larger the accelerator. On the other hand
the required quantity of superconductor Increases
faster than the design field . At very high field,
greater than about 11 T, the current carrying capaci-
ties of conmerclally available superconductors be-
comes too small for consideration. It 1s certain
that there will be an optimal cost at some Interme-
diate field. In addition, at very high energies,
synchrotron radiation, which increases as the local
field to the fourth power, may be a limiting consi-
deration because of the Increased refrigeration
load. A likely upper limit imposed by these consi-
deration 1s 10 T. This field was set as an ultimate
design goal for the magnets we are developing.
Material
Temperature Maximal Field
Nb-T1 4.3 K ST
Nb-T1 1.8 K 10 T
«>3Sn 4.3 K 10 T
Operation of magnets at l.Q K in liquid heliun
at atmospheric pressure is a fairly recent develop-
ment. It has been straightforward, considerably
simpler, and more reliable than many expected. The
experience of laboratories that work with magnets
in this temperature range is that the anticipated
problem of superleaks has not materialized. This
propitious result is because good seals (in particu-
lar, heliarc welds) for liquid heliun are also super-
*Tuid tight. The Nb-T1 dipoles tested generally
reach about 3OX higher fields at 1.8 K than at 4.3 K.
The design bore of an accelerator is determined
by cost, field quality, alignment accuracy, and the
ease with which the beam can be steered. Recent
experience at Fermi lab indicates that a 75 ran inner
winding dianeter is satisfactory for synchrotron
*This work was supported by the Director, Office of
Energy Resesearch, Office of High Energy and Nuclear
Physics, High Energy Physics Division, U.S. Dept, of
Energy, under Contract No, DE-AC03-76SF00098.
During the past year we have built and tested
three Nb-T1 dipoles. Two are of the layer design,2,3
as shown 1n Fig. 1, and one is of the block design,*
as shown 1n Fig. 2. Details of magnet design and
test results are similar ized in Table II and detailed
in the sections that follow. At present an addi-
tional Nb-Ti dipole of the layer design and a Nb Sn
magnet of the block design are being constructed.
The status of their fabrication and the planned tests
are also described.
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Hassenzahl, W.; Gilbert, W.; Taylor, C. & Meuser, R. LBL program of 1 meter long, 50 mm diameter bore, dipoles with fields greater than 8 tesla, article, August 1, 1983; [Berkeley,] California. (https://digital.library.unt.edu/ark:/67531/metadc1072648/m1/3/: accessed June 5, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.