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Vacuum vessel for the3D-printed UST_2 stellarator
Dr. Vicente Queral
National Fusion Laboratory
CIEMAT, Spain
Prague
Czech Republic
12 October 2015
22nd IAEA Technical Meeting on Research Using Small Fusion Devices
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Outline
▪ Background
▪ Concept of the UST_2 vacuum vessel
▪ Alternative 1. Light-formed metal liner
▪ Alternative 2. Thin electroformed metal liner
▪ Alternative 3. Internal film deposition
▪ Future work and conclusions
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Background
The work is developed in a framework of very lowfunds. Up to now only private funds (6000 €)have been obtained for the development andconstruction of UST_2. Essentially only oneresearcher working on the project.
The work is R&D and innovation inengineering.
The geometrical complexity of stellarators is one oftheir main drawbacks. Thus,
Objective of the work: Contribute to the constructionproblem of stellarators, particularly by AdditiveManufacturing (AM). Sub-objective: Try to lower thecost keeping reasonable performance.
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• Designed, built and operated by me from 2005 to 2007 in my personal laboratory, 3000 €.
UST_1 facility
Toroidal milling machine
Facility
Background. A previous UST_1
UST_1 inspired SCR-1, Stellarator de Costa Rica (same coil design
and shape)Picture courtesy of ITCR
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Hints on UST_2 design
Sketch showing the elements and geometrical concept of UST_2
Background
Elevation view
Plasma volume (litres) 9.5
R, major radius (mm) 292
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+
Resin casting, or other material, in the internal volume. The ‘mould’ remains attached to the resin.
Light truss structure covered by a thin shell, fabricated by additive manufacturing (internal surface removed in the figure).
Hints on UST_2. 3DformworkBackground
UST_2 will be built by the 3Dformwork method
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Concept of the UST_2 vacuum vessel
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Easier construction in companies.
Faster and more flexible maintenance.
Wide access through the ends of the sectors.
Also, advantages for reactors.
Separation in modules is favourable (both for small and
large stellarators)
1)
Concept of splitable stellarator
Detachable periods (Wang 2005)
UST_2 stellarator
Large vacuum flanges.
More vacuum issues.
Advantages
Drawbacks
(Wang 2005) X.R. Wang, et al. and the ARIES
Team, Fus. Sci. Tech. 47(4) 1074-1078, 2005.
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Several sectors joined by flanges
Concept of modular vacuum vessel
~ 700 mm
Flanges
Central VV Section
Curved VV Sector
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Sketch of the
liner/film concept
Fabrication approaches for the VV
1. Light-formed metal liner.
2. Thin electroformed metal liner.
3. Internal (thin) film deposition.
Based on an external plastic/resin structure
♦ Metal additive manufacturing is not considered, high cost (~ 5000-10000 € per liner and sector).
♦ Reliable traditional forge and weld methods (HSX, NCSX,
W7-X vessels) not considered since new methods are sought.
Alternatives:
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Alternative 1. Light-formed metal liner
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Shaping, fixing and Sn-Ag soldering Cu strips (0.3 mm thick) on the plaster form
Light-formed metal liner
Finished half vacuum vessel sector. Ribs pre-tinned Bi-Sn.
Plaster form
3D-printed mould for the plaster form and for other castings
Approach 1
Metal liner externally reinforced with epoxy resin
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Fixations to solder the large flange on the joined
Finished VV liner. Prepared for initial tightness tests
Soldering the two halves with Bi-Sn, from the interior of VV
Production of the copper liner
Light-formed metal linerApproach 1
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Approach 1
Soldering external claws (brass ball chain)
Curious picture of the 3D-printed mould for epoxy resin casting on the liner
Finished Curved VV sector. Copper liner epoxy reinforced.
External resin reinforcement
Light-formed metal liner
~ 3
00
mm
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Installed liner epoxy reinforced VVAssembling
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Vacuum vessel inside half Coil frame
Two halves of the Coil frame
Closure with the second half Coil frame. Modular vacuum vessel.
Assembling of a halfperiodAssembling
The VV is located inside two halves of Coil frame
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Half period finished and assembledAssembling
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The vacuum vessel achieved ~ 10-2 Pa (poor vacuum due to
low conductance due to e-gun and poor vacuum cleaning and
conditioning). E-beam validation of the sector were satisfactorily produced.
N202_F70-135.mpg
e-beam experiments performed in VV
Sketch of the e-beam experimental set-up
Validation
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2nd Alternative.Ongoing R&D
20End cut
Thin electroformed metal liner
1. Flange attachment. 2. Optionally external epoxy reinforcement, similarly to Approach 1.
Curved VV test sector produced by electroforming or electrodeposition
Cu electrodeposition (0.3-0.5 mm thick Cu layer)
Conductive paint (graphite
and silver)
Moulded wax mandrel
Thin electroformation on painted wax mandrel
Approach 2
~ 150 mm (scale 1/2)
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3rd Alternative.Ongoing R&D
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SLA 3D-printed internal surface (‘liner’) of Curved VV sector
Will try to lower cost keeping performance
Full flanges are being tried
Internal film depositionApproach 3
Internal metallic film
Option 3.1: Internal plastic ‘liner’
SLA = Selective Laser Sintering
Casting with resin
External 3D-printed mould
~ 3
00
mm
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Option 3.2: 3Dformwork structure
Internal metallic film
Filling with epoxy resin
Approach 3
Internal reinforcement bars of the 3Dformwork structure.
Model
Picture
Internal film deposition
~ 1
50
mm
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Alternatives to create a metallic film
Approach 3
PVD = Physical vapourdeposition
PVD. 10-2 Pa has to be achieved previous to PVD. Care needed since it is plastic and high T needed. Quite closed shape, thus uncommon PVD, therefore more expensive. Only thinfilm reasonable.
Conductive paint + Internal electrodeposition. Internal electrod. is uncommon, then more expensive. Possible thick film.
Electroless deposition. Specialized process. 1200$ for real size, Cu, 1
piece, 50 μm, USA company.
Being currently tested
Internal film deposition
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Vacuum is still too poor (>10-2
Pa) to attempt PVD
Assembled sector of VV under vacuum test
Approach 3 Internal film deposition
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Decision about the more economical alternative, for the same performance.
Fabrication of the remaining Curved VV sectors by such alternative.
Assembly of the sectors and achieve acceptable vacuum level.
Future work
To be achieved in the next year
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The alternatives are simple and of relatively low cost. But, still further assays are required to validate the concepts.
They may be useful to built vacuum vessels for experimental tokamaks, stellarators and other fusion devices.
Any country or small laboratory may be able to utilise such methods.
Conclusions
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More information in
www.fusionvic.org