Performance of W/Cu FGM in edge plasma of HT-7 tokamak

Zhu Dahuan Liu yang Chen Junling

Institute of plasma physics, Chinese Academic of Science, China

July 19-20, 2011 Hefei, ASIPP

Outline

1. Background and objectives

2. Plasma exposure of W/Cu FGM and W-La2O3 in HT-7

tokamak

- W/Cu FGM

- W-1%La2O3

3. Summary & future plane

2

W as PFM

Advantages• High melting point • Low sputtering yield• Promising thermal conductivity• Low tritium inventory

Fusion applications

Disadvantages

- Low temperature embrittlement- Recrystallization embrittlement- Radiation embrittlement- Mismatch with Copper based heat sink materials

Solutions

Grain boundaryweakening

◆ Engineer requirement ◆ Thermal mismatch

Macro-brush Mono-block W/Cu FGM 3

W/Cu FGM

W/Cu FGM• Smooth the composition transition

• One step processing (fabrication and jointing)

Materials processing

W or W-La2O3

layer W-20%Cu layer

W-40%Cu layer

W-60%Cu layer

W-80%Cu layer

pure Cu

Graded distribution

4

• Investigation on the performance of W/Cu FGMs in edge plasma exposure

- failure behavior

- failure mechanism

• Evaluation of the W-1%wt.La2O3 under plasma exposure

- Influence of La2O3 on thermal resistance

Objectives

5

Exposure of W/Cu FGM in HT-7 tokamak

◆ Main parameters:aL ~280mm,Ip~150KA, PLHCD~350kW,Total shots ~210 cycles, (#111377~#111587 )Average duration time ~1s.

Schematic of deviceW/Cu FGM block

（ 10 X 10 X 12mm）

Sample support

6

(b)

Failure behavior of W/Cu FGM under plasma exposure

Surface morphology Surface components analysis(XRF) Beside the initial compositions of W (99.92%) and Fe (0.07%), only little Ti, Cr and Mn (<0.1%)

※ No failure was found at interface, but surface was damaged.

※ cracks originated from the edge and propagated to the inside and interface.

Macro crack

Exfoliation

Termination

propagation along interface

Edge exfoliation

Cross-section morphology

Macro crack

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Center cracks and exfoliation

Micro crack

• Under quasi-stationary heat load ~2MW/m2(~1s)

maximum surface temperature is 107oC → embrittlement behavior

maximum stress at the interface is 57 Mpa

• But the damages occur at surface

• The damage cause by another reason.

Failure mechanism

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(a) Temperature and (b) Stress distribution under 2MW/m2 (1s)

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(a) 3D and (b) Surface distribution of von mises stress under typical transient flux 0.2 MJ/m2 (2ms)

• Under typical heat flux ~0.2 MJ/m2(~2ms)

maximum stress at the surface is 993 Mpa

• Stress singularity is basically accordance with the loop-like crack

• The damage at surface is likely to be created by transient flux and extend

by quasi-stationary heat load

(a)W-1%La2O3 composite; (b) pure W

• La2O3 caused the severe damages (severe large macro

cracks)；• Degradation of thermal conductivity may be the

reason.

W-1%La2O3under plasma exposure

Macro cracks

Exfoliation0 200 400 600 800 1000

60

80

100

120

140

160

180

W(theoretic) W-La2O3(theoretic) W(experiment) W-La2O3(experiment)

The

rmal

con

duct

ivity

(W

m-1K

-1)

Temperature (oC)

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W/Cu FGMs show good performance of interface to withstand such thermal fatigue in general;

W surface was destroyed by the typical high transient flux； - Cracks were initially created at surface edge, then extended deeply into the interface and would cause the failure of interface. - Formation of columnar crystal structure at surface may be advantageous for thermal resistance .

La2O3 dispersoid caused the severe damages. - W-1%La2O3 may be not fit as the PFM in currently tokamak device. - Optimization of the fabrication process and enhancing the thermal conductivity are critical issues for W- 1%La2O3 for fusion application.

Summary

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Use a electron generator to simulate the 2MW/m2(~1s) on W/Cu FGMs surface

Built some diagnostic technologies

-Infrared camera → Surface temperature -Thermal couple measurement → Body temperature

Future plan

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