1. D retention in O-covered and pure beryllium
Matthias Reinelt, Christian Linsmeier
Max-Planck-Institut für Plasmaphysik
EURATOM Association, Garching b. München, Germany
Outline:
Motivation
Experimental results  Interpretation
Retention
Sample characterisation
Mechanisms
Outlook
09 /10 July 2007

2. Investigation of the D retention in Be
Motivation 1: ITER C W
H,D,T
ITER cross section
~ 700 m2 Be
Implantation of D into Be first wall
Investigation of the D retention in Be
System Be – D (  Be – T)
Be : fast reaction with O2 and H2O
Previous
experiments : Often oxygen contaminated surface
Investigation of System Be – O – D
System Be – D : no data

3. Motivation 2: Literature
Diffusion: ED
0.04 to 2.5 eV
Solubility: ES
0.1 to 1 eV
Saturation
0.3 to 0.4 D/Be
...
[Anderl 1999]
0.1 – 60 keV
Retention adjusted for
100eV implantation
Possible sources of uncertainties
Chemical composition
Sample structure
Mechanisms
Variation of
1-2 ORDERS
OF MAGNITUDE

4. Surface characterization Retention mechanisms Influence of BeO
Issues:
Retention in pure Be
Surface characterization
Retention mechanisms
Influence of BeO

5. Experiment: Preparation
1 keV D+ Implantation
(Mass separated)
Retained quantity
Polished, single
crystalline Be
Cleaning:
3 keV Ar+
XPS/LEIS
Annealing (1000 K)
BeO coverage < 0.2 ML
mbar
up to 1000 K

6. Experiment: Retention
TPD
Temperature
Programmed
Desorption
QMS
„Retention“ =
TPD/NRA amount
Incident amount (measured current)
Desorption rate
NRA
D(3He,4He)p
Electron impact heating / TC

7. Experiment: Desorption
Sequential release of D
Energy barriers for ...
Diffusion
Detrapping
Recombination
Binding states of D
Retention mechanisms
TPD
Temperature
Programmed
Desorption
QMS
Desorption rate
Electron impact heating / TC

8. Issue 1:
Deuterium retention in pure Be

9. Retention at RT-implantation
1 keV D (exp.: 3 keV D3+)
Maximum
concentration:
D/Be = 0.35

10. Supersaturation  Structural modifications
Simulation: SDTrim.SP
SDTrim.SP not applicable
> max. concentration:
Supersaturation
D/Be = 0.35 Be
Erosion rate (sputtering) < Concentration build-up (implantation)
Supersaturation  Structural modifications

11. Retention: Literature

12. Retention: Elevated temperature
Review
[Anderl 1999]
Be (+ BeO)
1 and 1.5 keV
pure Be (1 keV)

13. Summary: Retention 1 keV Deuterium  clean beryllium
~80% Retention at low fluences
Saturation:
Retained areal density 2·1017 D cm-2
(reached at 2·1017 D cm-2 incident fluence)
Maximum local concentration D/Be=0.35
Local supersaturation in the bulk at 1·1017 D cm-2
Nearly constant retention up to 530 K
No significant influence of BeO coverage

14. Issue 2:
Surface characterization

15. Substrate properties: REM
Single crystalline (11-20) Be disk
(after several hours at 1000 K in UHV)

16. Substrate properties
90°, Zoom

17. Substrate properties (1010) (1120) (0001) T  1000 K, several hours:
Recrystallisation to low-indexed surfaces
Formation of facetted crystallites
 substantial process

18. Substrate properties Cleaning: Cycles of 3 keV Ar+ / 1000 K
 Recrystallisation + Erosion

19. Substrate properties: Deuterium irradiation
Cycles of
Cleaning
D Implantation
Degassing 1000 K

20. Substrate properties: Morphology
AFM
500 nm
Cycles of
Cleaning
D Implantation
Degassing 1000 K
+ Recrystallisation
+ Erosion
+ Structural modifications

21. Substrate properties: Elemental composition
(45°, 500 eV He+)
Be +
3 ML BeO
(surface layer)
clean Be surface +
3 ML BeO
(buried)
 Segregation of Be at the surface
 Annealing (Recrystallisation) of the surface above 1000 K

22. Summary: Surface characterisation
Annealing T  1000 K
Diffusion of Be
 Recrystallisation
Segregation of Be to the surface
 Coverage of thin BeO surface layers by Be
T  1000 K + ion bombardment
Erosion processes
+ recrystallization to single crystallinity
+ structural modifications

23. Issue 3:
Retention mechanisms

24. Temperature Programmed Desorption
NRA: retained amount
pure, annealed Be at RT
1 keV D+ implantation
saturation

25. Increasing fluence Low-temp. release: Structural modifications
High-temp. release: Trapping in defects (intrinsic or ion-induced)
local
saturation
of binding states

26. Increasing fluence
SDTrim.SP: Supersaturation
D/Be = 0.35

27. Implantation at elevated temperature
Expectation:
* no occupation of low temperature states
* retention loss of 30 %
measured: only 14%
retention at elevated temperature
is higher than expected
D from low temperature
stage is trapped differently
Phase transformation ?
Population / creation of
different binding states
300 K
530 K

28. Issue 4:
Influence of BeO coverage

29. Influence of BeO coverage
* Closed BeO coverage (3 ML) has no (measurable) effect on retention
* No shift of desorption states  no recombination-limited desorption mechanisms
* Additional state at 750 K: BeO – D ?

30. Modelling Desorption spectrum High temperature stage
Low temperature stage
Polanyi-Wigner-Equation
(Arrhenius expression)
High temperature stage
Rate-limiting step is
detrapping from bulk sites
 TMAP7
...
Desorption of surface
adsorbed gases
Diffusion, trapping and surface
recombination

31. High temperature stage: TMAP7
Parameters: Diffusivity, Solubility, Trapping / Detrapping rates,
Trap concentrations,...
Vacuum
const mbar
surface flux
rate dependent D Be
bulk with
2 traps
rate dependent, heating
surface flux

32. High temperature stage: TMAP7
 Model is reasonably
accurate
 Does NOT reproduce all details !
diffusivity, solubility, traps, profile...
... broaden peaks
Microstructure ?

33. Low temperature stage: PW
Input of measured temperature ramps into simulation !

34. Low temperature stage: PW

35. Energies: System Be – D E (D-Atom) Be bulk Vacuum E atomic D = 0 eV
Surface
Structural modifications
E atomic D = 0 eV
Ion induced defects

36. Energies: System Be – D E (D-Atom) Surface ED = 0.29 eV [Abramov]
D atomic E0≡ 0
+0.2 eV
ES = eV
EAd = eV
[Küppers]
-1.5 eV
-2.1 eV
-2.2 eV
D2 molecular
EBE (1/2 D2) = eV
Surface

37. Summary: Retention mechanisms
Retained amount < 1·1017 D cm-2
 Trapping in intrinsic / ion induced defects
Supersaturation > 1·1017 D cm-2
 Creation of structural modifications
 Binding of D to these modifications
Elevated temperature
 Change of the structural modifications
Thin BeO surface layers
 Surface has no recombination-limiting influence
 Binding as BeO-D

38. ✔ Summary Projection for ITER ✔ Retention of the pure Be wall:
net erosion areas
No isotope effects
Maximum retention for 1 keV / 0° incidence
< 7g T
Projection
for ITER
Retention of
Be wall
Mixed materials
pure Be ✔ ✔
BeXW
Be2C
BeO
WXC
WOX
Retention in Be with
mixed material surface layers

39. Summary Projection for ITER Implantation / Retention in ...
Mixed material
surface layers
Mixed
materials
Be – O – C – W
Be2C
BeO
BeXW
pure Beryllium
pure Substrate

40. Road map Expermental data for Be – D Experimental data:
TPD+NRA+XPS+ISS / REM+AFM
Modelling:
TMAP7
MD / DFT –
Calculations
Mixed Materials
Inventory and desorption from mixed materials:
THICK layers of BeO / Be2C / BeXW
Substrate evolution with implantation / temperature ramping: Ternary systems, Ultrathin carbon layers
Mixed material
surface layers
THIN surface layers of BeO / Be2C / BeXW
Retention + Mixing / Diffusion / Phases, ...