C. Björkas, K. Vörtler and K. Nordlund Department of Physics, University of Helsinki Joint...
-
Upload
lillian-schultz -
Category
Documents
-
view
213 -
download
1
Transcript of C. Björkas, K. Vörtler and K. Nordlund Department of Physics, University of Helsinki Joint...
C. Björkas, K. Vörtler and K. Nordlund
Department of Physics, University of Helsinki
Joint TFE-SEWG - Material Migration and Material Mixing meeting
MD study of erosion of Be and WC under D bombardment
Joint TFE-SEWG Material Migration and Material Mixing meeting
- Carolina Björkas2
ITER
First wall: Beryllium
Divertor strike point: CFC
Divertor baffle and dome: Tungsten
Plasma: D + T
How does Be erode due
to plasma impact?
How does the mixed WC
erode?
Joint TFE-SEWG Material Migration and Material Mixing meeting
- Carolina Björkas3
Method
We bombarded beryllium and WC surfaces with D ions In the Be case, we used both initially rough and perfect
(0001), (1120) ones For WC, both C and W determined surfaces were used 3 - 100 eV for Be and 100 - 300 eV for WC Flux ~2·1028 m-2s-1
Cell of ~3000 atoms
Distance 5 Å
Fixed bottommostlayers, temperaturecontrol at borders
Joint TFE-SEWG Material Migration and Material Mixing meeting
- Carolina Björkas4
D irradiation of Be
Sputtering is seen at 7 eV
A large fraction of Be is eroded as BeD molecules at low energies
Exps. are from Nishijima et al. Plasma Phys.
Control. Fusion 50 (2008) 125007 at fluxes
1-3·1022 m-2s-1 and temperatures < 400 K
New experiments are coming soon
Chemical sputtering!
Joint TFE-SEWG Material Migration and Material Mixing meeting
- Carolina Björkas5
D irradiation of Be
Joint TFE-SEWG Material Migration and Material Mixing meeting
- Carolina Björkas6
D irradiation of Be
Joint TFE-SEWG Material Migration and Material Mixing meeting
- Carolina Björkas7
D irradiation of Be
The movie shows a swift chemical sputtering process Low-energetic D ions release Be atoms from the surface
by breaking Be-Be bonds The SCS was not believed to be present in metals
This is possible since a surface Be atom that has bonds with D, has a weakened binding to the surface
At low energies, Be atoms are likely to have D neighbours The figure shows
the initial neighbours
of the sputtered
Be atoms
Joint TFE-SEWG Material Migration and Material Mixing meeting
- Carolina Björkas8
D irradiation of WC
A clear preferential sputtering of C was seen in the WC irradiation
Agrees with experimental findings
Joint TFE-SEWG Material Migration and Material Mixing meeting
- Carolina Björkas9
D irradiation of WC
300 eV D on WC resulted in collapsing amorphization First ~1000 impacts: creation of defects in sample In the following: D2 accumulation, collapsing of structureC: gray
W: magentaD: light gray
Joint TFE-SEWG Material Migration and Material Mixing meeting
- Carolina Björkas10
D irradiation of WC
Flaking was alsoobserved
C: grayW: magentaD: light gray
Joint TFE-SEWG Material Migration and Material Mixing meeting
- Carolina Björkas11
Conclusions
The D bombardment of Be showed a clear chemical effect
The swift-chemical sputtering mechanism is present
WC get amorphous due to D bombardment Even flaking is seen in a few cases
Joint TFE-SEWG Material Migration and Material Mixing meeting
- Carolina Björkas12
Thank you!