Structure for an LHC 90mm Nb3Sn Quadrupole Magnet Page: 3 of 4
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Fig. 5. Cut-away CAD model of the dummy coil's bore strain gages.
Flexible steel shim stock was used as leaf-springs to
provide the outward pressure on the rubber contact pads. The
ends of the leaf-springs were attached to aluminum end plates.
The end plates were drawn together by a threaded rod to
deflect the springs outward, against the bore surface.
Fig. 6. CAD model of Bore strain gage compression fixture (left); photo of
actuated, actual fixture (right).
The fixture and strain gage trace were installed in the
aluminum dummy coil and seem to have performed well
during curing process. After curing, it was observed that three
of the eight bore gages were only partially bonded against the
bore. The gages were hooked up to monitoring equipment
and an LN2 "dunk" test was performed on the dummy coil.
All 8 gages were active, but the same three indicated
ineffectiveness.
IV. DUMMY COIL-PACK PRE-ASSEMBLY
After the dummy coil was instrumented and assembled, the
load pads were assembled around it and bolted together to
make up the "coil pack" (Fig. 7). Care was taken to plumb
and level the load pads during the torque sequence so that the
assembled coil pack was close to the target dimensions. The
objective in assembling the coil-pack was to attain a square
cross-section so the room temperature pre-loading in the
loading structure will impart a symmetrical and uniform load
on the dummy coil.
Bladder Contact
/ Surface
Keyway For
Load Key
Load Pad
Fig. 7. CAD Image of Assembled "Coil Pack".V. ROOM-TEMPERATURE PRELOAD PROCESS USING
BLADDERS AND KEYS
The pressurized bladders act as internal presses, stretching
the outer aluminum shell by pushing against the yokes and
compressing the coils by reacting against the coil pack. This
creates clearance for the insertion of the load keys. The keys
were shimmed to a prescribed interference thickness that
imparted the target room temperature preload on the "coil
pack" after the bladders were de-pressurized. The four 69.8
mm x 1016.0 mm bladders were individually pressurized to
facilitate interference load key and shim installations per
quadrant. The goal was to end up with the same key thickness
at all 2x4 key locations. To reduce bladder pressure to stay
within the safe limits of the pump, the coil pack was preloaded
using three intermediate key sizes. Each intermediate key size
was introduced in sequence. After a key-pair in one quadrant
was inserted, the opposite quadrant was then pressurized and
preloaded, and so on. During this process, all the strain gage
arrays on the shell and dummy coil were continuously
monitored.
With the introduction of the final key size and the outer
shell attaining its prescribed design strain values (determined
by ANSYS), the bladders were deflated and pulled out. Fig. 8
plots strain from representative strain gage data measured on
the shell and the dummy coil during the loading of the first
intermediate key size.
Bladde Pressures ( rbitrar unit )
Q 3 2 4
w 5o Shell S rains ( )
r 0 -
-100C
Dumm Coil Strai (s-S)
-zoo<
07 075 0? 085 09
Time (hrs)
Fig. 8. Measured azimuthal strain sequence in the shell and dummy coil
while loading the first intermediate key size. Note the correlation of the shell
strains (tension-positive), dummy-coil strains (compression-negative) and the
bladder pressurization in each quadrant (Q1-Q4).
VI. COLD TEST AND RESULTS
The final structural assembly was mounted on our 813 mm
diameter magnet test cryostat and cooled to 80K with LN2.
Strain gauge measurements have been compared with the
results of a 3D finite element ANSYS model. The model,
described in detail in [4] (Fig. 9), computed the strain in the
shell and the dummy coil after assembly and during cool-
down. Contact elements were inserted between all the3
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Hafalia, A. R.; Caspi, S.; Bartlett, S. E.; Dietderich, D. R.; Ferracin, P.; Gourlay, S. A. et al. Structure for an LHC 90mm Nb3Sn Quadrupole Magnet, article, April 16, 2005; Berkeley, California. (https://digital.library.unt.edu/ark:/67531/metadc873822/m1/3/: accessed April 24, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.