Zhu dahuan liu yang chen junling institute of plasma physics chinese academic of science china
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July 19-20, 2011 Hefei, ASIPP. 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. Outline. Background and objectives Plasma exposure of W/Cu FGM and W-La 2 O 3 in HT-7 tokamak

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Zhu Dahuan Liu yang Chen Junling

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July 19-20, 2011 Hefei, ASIPP

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


  • Background and objectives

  • Plasma exposure of W/Cu FGM and W-La2O3 in HT-7 tokamak

    - W/Cu FGM

    - W-1%La2O3

  • Summary & future plane

W as PFM


  • High melting point

  • Low sputtering yield

  • Promising thermal conductivity

  • Low tritium inventory

Fusion applications


  • Low temperature embrittlement

  • Recrystallization embrittlement

  • Radiation embrittlement

  • Mismatch with Copper based heat sink materials

Grain boundary



◆ Engineer requirement

◆ Thermal mismatch


Macro-brush Mono-block



Graded distribution

  • Smooth the composition transition

  • One step processing (fabrication and jointing)

W or W-La2O3


Materials processing

W-20%Cu layer

W-40%Cu layer

W-60%Cu layer

W-80%Cu layer

pure Cu


  • 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

Exposure of W/Cu FGM in HT-7 tokamak

Schematic of device

W/Cu FGM block

(10 X 10 X 12mm)

Sample support

◆ Main parameters:

aL ~280mm,



Total shots ~210 cycles,

(#111377~#111587 )

Average duration time ~1s.

Failure behavior of W/Cu FGM under plasma exposure

  • Surface components analysis(XRF)

  • Beside the initial compositions of W (99.92%) and Fe (0.07%), only little Ti, Cr and Mn (<0.1%)

  • Surface morphology

Macro crack

Micro crack

  • Cross-section morphology

Center cracks and exfoliation

Macro crack


propagation along interface

Edge exfoliation



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

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

Failure mechanism

  • 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.

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

(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 andextendby quasi-stationary heat load

W-1%La2O3under plasma exposure

Macro cracks

  • La2O3 caused the severe damages (severe large macro cracks);

  • Degradation of thermal conductivity may be the reason.


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


  • 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.

Future plan

  • 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

Thanks for your attention!

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