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
7
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
8
(a) Temperature and (b) Stress distribution under 2MW/m2 (1s)
9
(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)
10
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
11
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
12
13