Thermal shield bowing in long superconducting magnets Page: 3 of 9
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would be tubes, not annular shells. Further, it was decided that only
tube would cool each shield. This eliminates the need for complex
manifolding and reduces the number of components crossing magnet
junctions. The drawback is that it introduces asymmetries in shield
thermal gradients during rapid cooldown.one
This report describes a project designed to study the feasibility of
calculating thermal distortions caused by these temperature gradients
using a finite element model of an early 10 K thermal shield. Of primary
concern are the deflections experienced during cooldown. This information
is required in order to evaluate the need for internal constraints and
bellows protection at magnet junctions.
SHIELD GEOMETRY
The SSC cryostat contains two thermal shields, one at 80 K and one at
10 K. The 10 K shield in Figure 1 is the subject of this study.
Surrounded by the 80 K assembly, it has a bending stiffness one-fourth
that of its 80 K counterpart and so is presumably more interesting from
the standpoint of transient thermal distortions.
Essentially, the assembly consists of 2-7.62 cm ID, 0.32 cm thick
tubes welded to 2-12.70 cm inside radius shells. The total length is 12.2
m. Supports are located at the center and at 1.63 and 4.88 m from center.
This spacing yields equal end and mid-span deflections for the coil
assembly which is supported at the same points. Off-center supports allow
the assembly to slide along its length which allows free longitudinal
thermal contraction.
DEFLECTION STUDY
It is desirable to be able to calculate thermal deflections in
thermal shields, particularly in early design stages, so that many options
may be evaluated without building prototypes of each. However, we must
build and test at least one assembly in order to verify the analytical
calculations.7.62 cmn
WIA0.32 em
4^0 cm10 K SHIELD CROSS SECTION
Fig. 1. 10 K shield cross section
2
TM-1351
0.32 ern
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Nicol, T.H.; Roman, M. & Fulton, S. Thermal shield bowing in long superconducting magnets, article, September 1, 1985; Batavia, Illinois. (https://digital.library.unt.edu/ark:/67531/metadc1056940/m1/3/: accessed April 23, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.