The way to a mock-up for divertor application

Max-Planck-Institut für Plasmaphysik

Johann Riesch ¹ , J. Almanstötter ² , M. Aumann ³ , J.W. Coenen ³ , H. Gietl ¹ , G. Holzner ¹ , T. Höschen ¹ , P. Huber ⁴ , M. Li ¹ , Ch. Linsmeier ³ , R. Neu ^1,5

1) Max-Planck-Institut für Plasmaphysik, 85748 Garching, Germany

Chemical deposited tungsten fibre- reinforced tungsten -

The way to a mock-up for divertor application

Contents

• W _f /W – state of the art

• W _f /W mock-up for divertor application

– Benefits

– Manufacturing concept

• Advanced methods

– Improved mock-up concepts

• PWI on W _f /W

• Summary

[based on Chawla 1993]

• Theory

W _f /W – state of the art

[based on Chawla 1993]

• Theory

• Synthesis

– Wound fibre preform (drawn W wire) + CVI (dual step)

 Model system

+ small bulk samples (2.5x3x25 mm)

W _f /W – state of the art

[Riesch et al., Phyisca

Scripta, 2015, accepted]

Toughening in as-fabricated state

Theory

matrix failure

Load [N]

Brittle

Stress-Strain curves of as-fabricated and heat-treated doped wire

T

[°C] As-fabricated 1300 1900 2300

σ _u [MPa] 2745±16 2221±12 1968±9 1274±105 ε _f [10 ^-2 ] 3.0±0.2 3.0±0.4 3.4±0.5 << 1.0

K doped tungsten wire

Embrittlement of pure W As-fabricated

1300 °C 1900 °C 2300 °C

[Riesch et al., Phyisca Scripta, 2015, accepted]

Unique benefit of W _f /W

Extrinsic toughening  no plasticity required

Works below DBTT

Works under embrittled state

(by neutron irradiation/high temperature)

Toughening range

Multi-fibre sample, 3-point bending

Toughening in embrittled state

Theory

Embrittled fibre

matrix failure

= bulk material failure

[Neu et al., Fusion Engineering and Design, 2015, submitted]

• Manufacturing technique identified + first samples

• High toughness in as-fabricated state

• Toughening in embrittled conditions

 Ranked as risk mitigation PFC/HHF material in EU Fusion roadmap towards DEMO

 Technological realisation

• W _f /W mock-ups according to ITER reference design

• Cyclic high heat load tests in GLADIS W _f /W – state of the art: summary

Mono block Flat tile

W _f /W mock-up for divertor application

Operation temperature window

Recrystallisation Inherent brittleness &

radiation embrittlement

Operation temperature window

Based on Zinkle et.al 2000 [S.J. Zinkle et al., FED 51-52 (2000) 55-71] and Timmis (CuCrZr) [Timmis, Material Assessment Report on the Use of Copper Alloys in DEMO (2012)]

Ductile fibre &

bridging/pull-out if embrittled Potassium doped fibre

Cracking of tungsten

Deep cracking of divertor elements

Electron beam (FE200, France), 20 MW/m

up to 1000 cycles, actively cooled

Result of low cycle fatigue (crack

initiation) and brittle behavior during

[Pintsuk et al., Fusion Eng Des 88 (2013) 1858– 1861]

Incoperate W _f /W

J-integrals for a pre-crack of 3 mm

Recrystallized tungsten Tungsten

Copper interlayer and CuCrZr tube

Pre-crack defined in the tungsten matrix

Tungsten fibres

(elastic) Heat flux

1

For fibres with a radius of 0.25 mm. A total debonding length of 500 µm is assumed.

2

G. Pintsuk et al. / Fusion Engineering and Design 88 (2013) 1858– 1861

3

a deformation factor of 30 is used for a better illustration.

x y z

Fibres

Stress distribution

in x-direction after high heat flux load of 20MW/m

(MPa)

Deep cracking

0 0.5 1 1.5 2 2.5 3 3.5

no fibre fibre (13%)

J-integral (mJ/mm2)

at the mid plane critical value

• Small scale mock-up for technology development and validation

 Possibility to produce W _f /W tiles

• Mono block: 28 mm x 28 mm x 12 mm

• Flat tile: 12 mm x 28 mm x 5-8 mm

Development towards application in DEMO

[Hirai et al., Fusion Eng Des 88 (2013) 1798 – 1801]

W-Wire

Plate

local heater WF

+ H

W-Deposit

Layered CVD

So far: Dual step CVI process

• Extensive investigations including modelling

• Complicated + time consuming process Layered CVD

• Positioning and ingrowing of fibre layer in alternation

• No deep infiltration necessary + easier handling and

process control

Layered CVD – results

No pores

• 50 x 50 x 3.5-4 mm ³ , 194 g

• 10 Layers a 220 fibres (pure), fibre volume fraction ≈ 0.3, unidirectional

• 93 – 98 % depending on location, 94.2 % overall density (Archimedes)

• Fibre arrangement crucial for density

Charpy impact testing

Drag indicator

Sample

)

( H h

mg Energy

Charpy  

m

KLST-type sample

Tests conducted at Institute of

Materials Science and Mechanics of Materials, TU Munich

[Macherauch, Praktikum in Werkstoffkunde, 1972]

Charpy impact testing

0.83 0.78

0.64

0.88

0.73

E ner gy [J] W _plate (300 °C) = 0.0

W plate, annealed (1000 °C) = 0.0

Advanced methods

Textile techniques

WILMA: W Infiltration Machine

W Infiltration Machine WILMA new installation of

CVD/CVI setup at FZ Jülich fully commissioned

Gas inlet Vessel

Vacuum Pump

Liquid Ring Pump

Ventilation system

Scrubber Tank

• first W CVD successfully performed

• full operation starts this November

heatable table

Modelling: Pore infiltration

Reaction mechanism: WF ₆  3 H ₂  ³⁰⁰  ^  ^{C  800}   ^{ C}  W  6 HF

Transport by

Diffusion + Convection

Growth rate

Rate determining step = dissociation of H ₂

Improved mock-up concepts

“tungsten wire fabric is slowly wound round a heated Cu-Tube in atmosphere of WF ₆ + H ₂  continuous deposition of W”

heating from the inside

WF

+ H

W-Wire W-Deposit

Cu-Tube

Spark erosion of contour

„Wound tube“

“Fibrous preform of tungsten wire is infiltrated by WF ₆ + H ₂ . Defined process controlling allows to fully infiltrate the preform in the upper half and forms a graded transition in the lower half”

local heater

WF

+ H

W-Wire

W-Deposit

Cu melt infiltration

Drill cooling channel Graded

transition Woven

3D preform

„Graded transition“

Infiltration of W _f fabric stack

Thermocouple

W _f fabric stack

Plasma wall interaction

Tungsten fibre-reinforced tungsten

• Special microstructure

 Fibre, Matrix

• New materials

• Interfaces, Doped W wire

• Complex structures

• Internal Interfaces, various constituents (fibre, matrix, interface)

 Many aspects to be considered if used as plasma facing material e.g.

• Thermal stability

• Activation

• Interaction with hydrogen

• Erosion

• …

• W _f /W shows toughness in as-fabricated and embrittled conditions

• A divertor made of W _f /W can increase the temperature window and solve cracking problems

• A layered CVD process allows production of W _f /W tiles in reasonable size and quality

 Charpy impact test

• Advanced methods are developed

 W _f fabric production

 WILMA

 Modelling

 Improved mock-up concepts now feasible

• Many aspects to be considered if used as plasma facing material

Summary