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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