A new support structure for high field magnets Page: 2 of 4
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II. CONCEPT OF OPERATION
Tensil Tensile
- f
an nva-- Lorentz
-fr
Fig. 3, Force Diagram: RT-1 Magnet Loading Design (top) vs. RD-3 Loading
Design (bottom)
The large Lorentz forces make the use of a cantilever
structure (Fig. 3, top) too soft. That effect was demonstrated
in magnet RT-1 where the structure allowed the coil halves to
separate more than 1.5 mm at 12 T. The use of a circular
shell is more efficient in providing pre-stress that can
effectively prevent the coils from separating. The force
balance between shell and coils takes place in several steps.
Initially the shell pre-stress is set to 20.3 ksi [140 MPa] by the
bladders and keys. During cool-down the stress increases to
39.2 ksi [270 MPa] and remains unchanged during operation.
The force on the shell is reacted by the force between the
symmetrical halves of the magnet (Fig. 3 bottom). We expect
most of the reactive force to be carried by the iron pole. The
Lorentz force loads the coils and unloads the bore, posts and
side rails. The coil modules will separate only after the
Lorentz force overcomes the reactive force, which is not
expected to happen below 16 T - well above the short-sample
field for RD-3.RD3v10 - inserted key + cool down to 4.3 K
force, Mu=
ANSYS 5.6.1
MIAY 22 2000
08:07:20
STEP=5
SUE =2
TIME-5
SEQV (A,
Powe rcr-chac
F FAET-,DNL< .00
40
60
o.16
.2
o 2
o 2
.2BE
E0-
E+-
E0-
70-Fig. 4, ANSYS analyses at 4.3K and magnet at maximum Lorentz forces.
LBNL-47796
SC-MAG 738
The integrated double bore Lorentz force at 16 T is
F,=1.5x106 lbs/ft [22 MN/m], Fy=-2.1x105 lbs/ft [-3.0 MN/m]
and Fz=1.57x105 lbs [700 KN]. The program ANSYS was
used to calculate the magnetic forces and perform the
structural analysis (Fig. 4). The load case progression
followed the steps of assembly, cool-down and 16 T Lorentz
load and was later confirmed by strain gauge measurements.Coil Modules
Keys~ ,/>~
Iron Yoke
p
1~M adder
- -
I ron Pole
- -- - IroAluminum Shell
Fig. 5, RD-3 Loading Structure components.ni
Support
PadIII. LOADING STRUCTURE DESIGN
A. Components
The basic loading structure consists of the following
components - a pair of ferrous steel "yoke-stack" assemblies;
a single aluminum cylindrical "shell"; a set of 4 interference
keys (hardened steel bars); and the magnet coil-pack itself
(Fig. 5). A "temporary", but essential component in the
assembly are the bladders. The bladders used in the
assembly process provide the primary force that spreads the
yoke stacks apart within the cylindrical shell, thus stretching
the shell to provide the compressive force that preloads the
coil-pack. Once the structure is "locked" in place with the
interference keys, the bladders are deflated and removed.
B. Shell
The shell provides the ultimate preload on the magnet coil-
pack. During cool-down, it essentially doubles its preload on
the coil-pack, through thermal contraction. The design pre-
load at 4.3K is high enough to maintain a stable structure up
to a 16 Tesla field.
The shell material used is a 2219-T852, aluminum alloy tube
forging - selected for high resistance to crack propagation.
To further address the crack propagation concern, a material
quality specification similar to ASTM B247 was called out.
An ultrasonic inspection specification (ASTM 8594, Class A)
was also called out. The shell finish dimensions are: OD of
29.134" [740 mm]; ID of 25.984" [660 mm] and length of
34.481" [875.82 mm]. The ID surface finish was specified at'N
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Bish, P. S.; Caspi, S.; Dietderich, D. R.; Gourlay, S. A.; Hafalia, R. R.; Hannaford, R. et al. A new support structure for high field magnets, article, June 15, 2001; Berkeley, California. (https://digital.library.unt.edu/ark:/67531/metadc743221/m1/2/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.