1. Studies of impurity migration in TEXTOR by local tracer injection
A. Kirschnera, P. Wienholda, D. Borodina, C. Björkasa,b, O. Van Hoeyc, D. Matveeva,c,
S. Brezinseka, A. Kretera, M. Laengnera, K. Ohyad, V. Philippsa, A. Pospieszczyka,
U. Samma, B. Schweera, and TEXTOR teama
aInstitut für Energie- und Klimaforschung – Plasmaphysik, Forschungszentrum Jülich, Assoziation EURATOM-FZJ, Trilateral Euregio Cluster, Jülich, Germany, bDepartment of Physics, University of Helsinki, Finland, cDepartment of Applied Physics, Ghent University, B-9000 Ghent, Belgium, dInstitute of Technology and Science, The University of Tokushima, Japan.
Motivation
ERO modelling results
● Former tracer injection experiments in TEXTOR lead to very small local deposition efficiencies. According modelling needs assumption of enhanced re-erosion (factor fEnh) of re-deposits to match.
● Possibly enhanced re-erosion of re-deposits: determines resulting net-deposition and thus important for wall life time.
● Study the influence of flux and energy of depositing tracer species on resulting deposition efficiency ⇒ involved mechanisms?
Modelled 13C deposition efficiencies
RI=0.1, RN=1
fEnh=5, RN=1
The 3D Monte Carlo code ERO
CH4
Cx+,CHy0,+
re-eroded/
reflected particles
background - plasma
surface (substrate C, CR, Be)
surface
plasma-wall-interaction:
physical sputtering/ reflection
chemical erosion (CD4, BeD)
deposition from background
redeposition of eroded species
impurity transport:
ionisation, dissociation
friction, thermal force
Lorentz-force
cross field diffusion
● Assuming reflection for hydrocarbons according to MD (RI=0.1, RN=1)
- to simulate observed 13C deposition efficiency: fEnh~35 for reference case, fEnh=10-15 for low injection case
● Assuming fEnh=5 for re-erosion and RN=1
- to simulate observed 13C deposition efficiency: RI= for reference case, RI= for low injection case
Modelled and simulated profiles of 13C deposition
Reference Case:
Low Injection Case:
13CH4 tracer experiments
Experimental set-up:
Test limiter after exposure:
horizontal
observation
vertical observation
toroidal
limiter
(46cm)
limiter lock
test limiter
Reference:
0.3%
polished C surface
● Reference case: RI>~0.9 needed to reproduce measured profile
● Low injection case: profile shape reproduced also for smaller RI
Low injection rate :
0.71%
Conclusions
Erosion: Y
Re-erosion: fEnh×Y
re-deposit D+
substrate
RI=0.1, RN=1
fEnh in ERO
Reference 35
Low injection
10-15
Biased test limiter
5-10
polished C surface
13CH4 injection rate
Limiter tip position
Reference
~1⋅1019/s
46cm
Low injection
~1⋅1018/s
46.2cm
Biased test limiter (300V)
47cm
Biased test limiter:
1.7%
● Measured 13C deposition efficiency
increases with impact energy and
reduced flux of depositing species
● “Standard” assumptions in ERO lead to
large 13C deposition efficiencies (55% for reference, 34% for low injection, 42% for biased limiter case)
● ERO needs enhanced re-erosion and/or increased ion reflection – enhancement smallest for biased limiter.
FEnh = F(Ein, Gin)
polished C surface
Deposition efficiency:
#deposited 13C on test limiter
#injected 13CH4 atoms