Office of Science Project Review Cryostat, WBS171
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Transcript of Office of Science Project Review Cryostat, WBS171
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Office of Science Project ReviewCryostat, WBS171
August 15-17, 2007
NCSX
Fabrication, Operations, and Maintenance Division
Engineering Department
Princeton Plasma Physics Laboratory
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The cryostat (WBS 171) is an insulating, semi-hermetic barrier that will allow the surrounding of the stellarator core with a cold, dry nitrogen blanket down to a temperature of 77K.
The semi-hermetic nature of the cryostat excludes the components of atmosphere from approaching the stellarator core in the design temperature range (77K to 311K).
Introduction: What is the Cryostat?
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The cryostat’s many versions have all had the same basic shape: One that be affords access to the port extension flanges.
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– Must be gas-tight to tolerate slight internal positive pressure
– Must provide penetrations for vessel extensions, electrical & hydraulic lines, stellarator supports, etc.
– Shall be of *demountable* design – Shall withstand vacuum boundary displacements
due to thermal expansion/contraction– The cryostat design, including penetrations and joint
sealing, shall limit the influx of ambient heat to about 13.9 kW (includes WBS 172, machine base)
Cryostat Requirements
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Interface Control
• The cryostat has interfaces with many systems (buswork, coil cooling, cryostat cooling, diagnostics, etc.)
• Notably, Diagnostics will have ever-evolving interfaces
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Current Concept
• The current cryostat concept has double mechanical strut located at the upper, outer, and lower aspects of each TF coil– Basic shape is
described by struts on radial planes
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NCSXCurrent Concept
• An FRP panel bridges two struts as a substrate• A glued 16 cm pyramid of polyurethane foam is
applied to the substrate
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Current Concept
• Lapped layers of flexible foam laid into the steps of the rigid foam pyramids with clamping/beauty panels finish the assembly
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Material Thermal Conductivity Coeff of Thermal Expansion
Dow Super-Tuff R Closed Cell Foam
0.033 W/mK @ 293K 9e-5 /K @ 300K
Unknown @ 77K
Inspec Solimide Open Cell Foam
0.040 @ 293K Resilient at all temperatures of interest
Extren FRP
(Inconel 718 is similar)
0.85 W/mK @ 300K
0.30 W/mK @77K
1.16e-5 /K @ 300K
5.5e-6 /K @ 77K
Teflon 0.26 W/mK @ 300K
0.23 W/mK @77K
4.2e-5 /K @ 300K
3.4e-5 /K @ 77K
304 SS 14.9 W/mK @ 300K
8.2 W/mK @77K
1.6e-5 /K @ 300K
7.5e-6 /K @ 77K
Thermal Characteristics of Materials
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The 0.033 W/mK associated with the candidate foams suggest a constant heat load of about 5 kW through the panels only.
5 kW suggests the vaporization of 4900 gallons of LN2 or¾ trailers per week
The GRD requires a maximum non-bakeout parasitic load of 2.12 trailers per week
The panels claim 36% of this number
Heat Load
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NCSXR = 152 cm
Vertical Port
R = 193 cm
Outboard Leg
R = 320 cm
Midpland Diag Cover
Cryostat, G-10
300K to 80K
-0.35cm -0.44 cm -0.74 cm
Vessel and Graded Extensions, Inconel
300K to 650K
0.65 cm ~0.8 cm(assuming some gradients in ports & ext.)
Machine Base, 300 Series SS
300K to 80K
-0.56cm
Differential expansion between the vessel and the penetrations is not trivial at 1 cm & 1.5 cm!
The cold innermost seals must tolerate this displacement
Differential Thermal Expansion
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• Dow Super-Tuff R– Closed cell polyisocyanurate foam available
for $0.60 per board foot
Why closed cell? Avoids condensation of moisture in bulk with consequent increase of k-factor
Main Insulation
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Main Insulation
• Coil Test Facility’s pump skid and coil cryostat used 17 cm of Dow Super Tuff-R– Very successful, no condensation
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• Inspec’s Solomide polyimide open-cell foam has a k-factor of .040 W/mK and retains its resiliency at 77K. – Open cell nature is undesirable
• Sub-mil Mylar is required between layers
– $8.50/bd ft
Flexible Insulation
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• Development jobs– Edge seal demonstration fixture is required
Development