eV range where GROSS sputtering yield of tungsten drops to 10 X greater than the required NET sputtering yield Reactor divertor lifetime 10 8 s requires net erosion rate of 10 6 100 X required net yield ID: 628238
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Slide1
Divertor plasma temperature in the ~ 10 eV range where GROSS sputtering yield of tungsten drops to ~ 10 X greater than the required NET sputtering yield.Reactor divertor lifetime ~108 s requires net erosion rate of 10-6
~ 100 X required net yield
~ 10 X
~ 1 X
Reactor
:
high plasma performance and high PFC lifetime requires strong re-deposition to ensure low net erosion
net
erosion
erosion
net
deposition
D
X
Main chamber erosion due to ions and high energy CX neutrals (ITER: E
CX
~ 500
eV
; DEMO = ??)
If re-deposition of W at main chamber is not increased, massive amounts of W migrate to
divertor
(t/
yr
)
R
Behrisch J. Nucl. Mater 313 (2003) 388
K Krieger J.
Nucl
. Mater 266 (1999) 207Slide2
W sputtering, L-mode, Inter-ELM, JET and AUGW sputtering of AUG DIV1 cannot be simply explained by TRIM modelW sputtering in JET L-mode can be well explained by sputtering with Be2+ JET Inter-ELM data have larger spread (reason could be using local Be flux data)TRIM tends to overestimate sputtering
K Krieger J.
Nucl
. Mater 266 (1999) 207
G van
Rooij
J.
Nucl
. Mater 438 (2013) S42
N
den Harder et al.
Nucl
. Fusion 56 (2016) 026014Slide3
Prompt re-deposition, JETWII spectroscopy might allow for in-situ prompt re-deposition estimation and hence would allow for 1st order estimation of net erosionWII (364.1nm) / (WI 361.7nm) line ratios were investigated at JETComparison for 2 JET discharges showed good agreement with simple re-deposition formula
Challenge: getting good spectroscopy data in high density discharges
G van
Rooij
J.
Nucl
. Mater 438 (2013) S42Slide4
W sputtering, Inter-ELM, DIII-DInter-ELM W erosion profile can be well explained by C-> W sputtering with OEDGE/ERO modeling in strongly attached (high Te
) dischargesTRIM overestimates sputtering yield at high
Te and underestimates at low TeLarger scatter of data below 10 eV
T
Abrams et al., PSI 2016Slide5
Intra-ELM W erosion (JET)Divertor erosion is dominated by ELMs for large ELMsW erosion cannot be explained by Be. D sputtering and possibly W self sputtering plays a larger roleW source correlates strongly with ELM energy loss
N
den Harder et al. Nucl
. Fusion 56 (2016) 026014Slide6
Effect of ELMs on W erosionNear surface content has strong influence on damage thresholdWhat is the real damage threshold for ELMs?
G de
Temmerman Veldhoven 2011Slide7
High fluence and frequent ELMs might change W erosion processes
T
Loewenhoff et al., Nucl. Fusion 55 (2015) 123004
M
Tokitani
et al.,
Nucl
. Fusion
51
(
2011) 102001
MJ Baldwin et al.,
Nucl
. Fusion 48 (2008) 035001
S Lindig et al., Phys. Scr. T145 (2011) 014039
Tungsten100000 pulses @ 0.3 MJ/m2Tungsten
Tungsten
Y Ueda et al., Fus. Sci. Technol. 52 (2007) 513
TungstenTungsten
Unipolar arcing, can possibly create W dust of nm size
High energy density plasma changes:
Surface
area; Surface roughness
Surface
potential (unipolar arcing may occur)Surface temperature (loosely bound layers, He bubbles)Surface chemical activity
Consequences:Chemical and physical erosion yieldRelation between gross erosion and net erosionDust production might occur due to macroscopic erosion of surface structure and meltlayer splashing
Whole grain ejection can cause macroscopic erosion
M Wirtz et al., J. Nucl. Mater. 420 (2012) 218
J
Coenen
et al.,
Nucl
. Fusion
51
(
2011) 083008
Meltlayer
splashing creates W dust of
m
m sizeSlide8
Research needsNarrow down uncertainty in physical erosion yield, TRIM tends to overestimate sputtering yieldIn-situ determination of net erosion yield is neededInvestigation of the material mixing effect in surface on W physical sputtering yield (implantation of He, N, Ne, Ar etc.)Quantification of high
fluence effects on surface evolution and changes in physical sputtering rateDevelopment of erosion model for ELM cycle taking into account kinetic effects of transient electron flux, transient deuteron flux, transient impurity fluxes under the condition of changing electric fields and changing background
plasma, and benchmarking to experiments (will require more sophisticated diagnostics)Evaluation of other macroscopic erosion processesEffect of neutron irradiation on W erosion