Key properties of mixed W-C-D surface related to tungsten erosion
The erosion of tungsten exposed to the mixed particle flux of carbon and deuterium ions is effected by several factors. The main factor is the formation of mixed W-C-D surface, which decreases content of tungsten atoms in the near-surface region. Other factors affect carbon content on the surface an...
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| Zitieren: | Key properties of mixed W-C-D surface related to tungsten erosion / I.A. Bizyukov // Вопросы атомной науки и техники. — 2010. — № 6. — С. 91-93. — Бібліогр.: 10 назв. — англ. |
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| citation_txt | Key properties of mixed W-C-D surface related to tungsten erosion / I.A. Bizyukov // Вопросы атомной науки и техники. — 2010. — № 6. — С. 91-93. — Бібліогр.: 10 назв. — англ. |
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| description | The erosion of tungsten exposed to the mixed particle flux of carbon and deuterium ions is effected by several factors. The main factor is the formation of mixed W-C-D surface, which decreases content of tungsten atoms in the near-surface region. Other factors affect carbon content on the surface and attributed to elevated surface temperature: chemical erosion and radiation-enhanced sublimation.
Распыление поверхности вольфрама, облучаемого смешанным потоком частиц углерода и дейтерия, находится под влиянием нескольких факторов. Основным фактором является формирование смешанной W-C-D поверхности, что уменьшает количество атомов вольфрама в приповерхностной области, откуда они распыляются. Другие факторы, такие как химическое распыление и радиационно-усиленная сублимация, влияют на концентрацию углерода на поверхности и связаны с ее повышенной температурой.
Розпилення поверхні вольфраму, опромінюваної змішаним потоком частинок вуглецю й дейтерію, знаходиться під впливом кількох факторів. Основним фактором є формування змішаної W-C-D поверхні, що зменшує кількість атомів вольфраму у приповерхневій області, звідкіля вони розпилюються. Інші фактори, такі як хімічне розпилення та радіаційно-посилена сублімація, впливають на концентрацію вуглецю на поверхні і пов'язані з її підвищеною температурою.
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KEY PROPERTIES OF MIXED W-C-D SURFACE RELATED
TO TUNGSTEN EROSION
I.A. Bizyukov
V.N. Karazin Kharkov National University, Kharkov, Ukraine
E-mail: ivan.bizyukov@mail.ru
The erosion of tungsten exposed to the mixed particle flux of carbon and deuterium ions is effected by several
factors. The main factor is the formation of mixed W-C-D surface, which decreases content of tungsten atoms in the
near-surface region. Other factors affect carbon content on the surface and attributed to elevated surface temperature:
chemical erosion and radiation-enhanced sublimation.
PACS: 79.20.Rf
1. INTRODUCTION
The current ITER design envisages beryllium at the
first wall, tungsten coatings in the baffle region of the
divertor and graphite-based components for the target
plates exposed to the high-heat flux [1]. The proximity of
the tungsten and carbon surfaces will unavoidably lead to
formation of the mixed surface, which will be exposed to
mixed particle flux. Erosion of tungsten surface due to
sputtering should occur under rather complicated
conditions. The incident ion flux includes fuel ions, as
well as neutrals and energetic carbon ions. This should
lead to formation of the mixed W-C-D surface, which
properties are generally different from properties of pure
materials.
The erosion of the mixed surface may be further
complicated by the temperature of the surface. At
elevated temperatures carbon prone to chemical sputtering
[2] and radiation enhanced sublimation [3]. The present
paper reviews the system of W surface exposed to C and
D ion flux, which demonstrate complicated physical
effects, influencing each other and defining the lifetime of
W surface.
2. FORMATION OF MIXED W-C-D SURFACE
The experiments and simulations on simultaneous
bombardment of W surface with C and D/He ion beams
have been performed in [4,5]. Because the usage of D and
C simultaneously may disturb the measurements due to
chemical erosion, one considers the formation of the
mixed surface replacing D with noble He gas.
Fig.1. The evolution of W sputtering yield towards steady-
state. Initially pure W surface is exposed to 3 keV He and
6 keV C ion beams (15% of C fraction)
When pure W surface is exposed to C and He ion
beams simultaneously, the W sputtering yield changes
with fluence. Fig. 1 shows the evolution of the yield as
obtained by TRIDYN [6] simulations.
The yield is high at the beginning due to purity of the
surface. However, implanted C atoms create the layer of
the mixed material with typical thickness of 10…15 nm.
As a result, W erosion decreases, because its
concentration at the surface is also decreases. This
continues until the system reaches the steady-state; in this
example it is reached at fluence 3×1018 cm-2, at higher
fluence the sputtering yield remains constant.
In steady-state regime, the number of implanted C
atoms equals to number of sputtered and reflected ones;
the surface composition and depth elemental distribution
remains the same. Fig. 2 shows the areal density of the
retained C atoms as a function of the C fraction in the
total flux. One can see that C areal density increases
monotonically with C fraction in the total flux until the
system switches into C deposition regime. The numerical
simulations with TRIDYN show good agreement with
experimental measurements.
Fig.2. The dependence of C areal density on C fraction in
total flux. W surface is exposed to 6 keV C and 3 keV He,
the data are represented for the steady-state
While C content in the surface is increasing, the
corresponding sputtering yield is remained approximately
constant, as shown in Fig. 3. The results of experiment and
the simulations agree well, with typical deviation of about
30%. The deviation is conditioned by error in the fluence
measurement. The simulations indicate also that the
sputtering yield drops dramatically approaching the
transition from sputtering regime to C layer deposition one.
A linear growth of sputtering yield, as plotted with
dots in Fig. 3, would only occur if it was independent of
PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY. 2010. № 6. 91
Series: Plasma Physics (16), p. 91-93.
mailto:ivan.bizyukov@mail.ru
the elemental composition of the mixed surface. In other
words, the sputtering rate of W atoms YW in that case
would be determined only by the fraction of the
contributing ion species in the total incident flux (fC or
fHe):
He
WHe
C
WCW YfYfY += ,
where and are sputtering yields of pure W due to
C and He ion impact respectively. Obviously, neglecting
the modification of the elemental composition can lead to
large errors in the simulation of W sputtering by
simultaneous impact of volatile and non-volatile
elements.
C
WY He
WY
Fig.3. The dependence of W sputtering yield on C fraction
in the total flux. W surface is exposed to 6 keV C and
3 keV He, data are represented for the steady-state
Therefore, the formation of the mixed surface leads to
increase of C and decrease of W concentration. The
number of W atoms available for sputtering is lower in
comparison to the pure surface; instead, implanted C
atoms take part in sputtering. As a result, the processes
attributed to W sputtering are partly replaced with those
providing C recycling (i.e. implantation and sputtering).
However, the balance defining the C recirculation can
be disturbed by temperature effects, which may decrease
the C concentration in the surface.
3. THE TEMPERATURE EFFECTS
Surface temperature introduces mechanisms, which
may increase the erosion of C atoms. These mechanisms
are known as chemical sputtering [2] and radiation
enhanced sublimation [3].
The mechanism of chemical erosion envisages that C
and D atoms create chemical bonds and form volatile
molecules, meanly methane, which leave the surface and
take away C atom. The methane production yield has been
measured as a function of the surface temperature and this
dependence has been studied experimentally in [7].
Typical example of such dependence is shown in
Fig. 4. The methane production exhibit the highest rates at
RT followed by a decreasing trend with increasing
temperature to ~ 500 K, followed by a leveling off at
higher temperatures. In order to compare the present
methane production levels with published methane yields
for graphite, we shall normalize the measured production
rates by the D ion flux incident on the specimen. We note
that the so derived ‘apparent’ yield is over-estimated due
to the inclusion of possible wall contributions. The
magnitude of the near-RT yield appears to be
approximately (7…10)×10-3 CD4/D. It is evident from
Fig. 4 that the temperature-dependence of CD4
production, obtained in this study, totally differs from
published yields for pure carbon [8]. While the ‘apparent’
yields are approximately equal to those of pure graphite at
RT, the normally seen graphite peak at ~750 K is not
present.
Fig.4. CD4 production rate as a function of specimen
temperature for simultaneous bombardment of W with 6
keV/C and 100 eV/D ions. Symbols of the same shape
represent data obtained on the same day. Methane yield
for pure carbon [8] is shown for comparison
The experimental results on the reemission of C due to
radiation-enhanced sublimation from tungsten during
irradiation with 6 keV C ion beam have been published in
[9]. At temperature 1373 K the C reemission from the
mixed W-C layer is generally lower than that from the
pure carbon. Since the setup has not allowed to study the
temperature dependence of C reemission from the mixed
W-C surface, it has been left unknown, whether the
generally lower value prevails at temperatures other than
1373 K.
In the temperature range below 1073 K, i.e., where
diffusion does not deplete the carbon from the surface, the
radiation-enhanced sublimation has been studied by
comparing C profiles at room temperature and at
temperature of 973 K. It has been confirmed that the
profiles are quite similar: C concentration at the very
surface is about 40-50%; it is decreasing deeper into the
surface until a depth of ~10 nm. Therefore, there is no
significant erosion mechanism (RES or otherwise)
contributing to the removal of carbon at T = 973 K as
compared to 300 K.
According to [10], the mechanism for RES relies on
the transport of C interstitials to a surface where they may
desorb. The nature of the mixed C-W surface layer may
act to impede this transport, as compared to pure graphite.
4. CONCLUSIONS
This work has reviewed the main factors affecting the
erosion rate of tungsten surface exposed to mixed C and
D particle flux. The formation of the mixed surface is
considered as the main factor, because the processes
92
93
attributed to W sputtering are partly replaced with those
providing C recycling.
Other factors related to surface temperature, like
chemical sputtering and radiation enhanced sublimation,
regulate C content in the mixed surface. However, they
have minor impact on tungsten erosion in the temperature
range, expected on surface in ITER divertor. Therefore,
the existing models simulating the interaction of ions and
neutrals with surface are suitable for use in ITER design.
The simulation programs (TRIDYN for example) can
provide numerical data for the case of the mixed surface,
which are well supported by experimental measurements.
One should take into account the dual influence of
temperature effects on formation of the mixed surface. On
the one hand, pure carbon surface, which may be formed
due to deposition, is prone to higher sputter rates at higher
temperatures. This should act preventing the carbon over-
layer on top of mixed W-C-D surface. On the other hand,
temperature effects are almost negligible for the mixed
W-C-D surface in the temperature range, typical for
ITER. Therefore, role of the temperature effects is
uncovering of the mixed surface.
REFERENCES
1. R.E.H. Clark, D.H. Reiter. Nuclear Fusion Research:
Understanding plasma surface interactions. Springer,
2005.
2. J. Roth, C. Garcia-Rosales. Analytic description of the
chemical erosion of graphite by hydrogen ions //
Nuclear Fusion. 1996, v. 36, p. 1647, with
corrigendum in Nuclear Fusion. 1997, v. 37, p. 897.
3. J. Roth, J. Bohdansky, K.L. Wilson. Erosion of carbon
due to bombardment with energetic ions at
temperatures up to 2000K // J. Nucl. Mater. 1982,
v. 111-112, p. 775.
4. I. Bizyukov, K. Krieger. Transition from tungsten
erosion to carbon layer deposition with simultaneous
bombardment of tungsten by helium and carbon //
Journal of Applied Physics. 2007, v. 101, p. 104906.
5. I. Bizyukov, K. Krieger. Principal processes occurring
at simultaneous bombardment of tungsten by carbon
and deuterium ions // Journal of Applied Physics.
2007, v. 102, p. 074923.
6. W. Moeller, W. Eckstein, J.P. Biersack. TRIDYN -
binary collision simulation of atomic collisions and
dynamic composition changes in solids // Comput.
Phys. Commun. 1988, v. 51, N 3, p. 355-368.
7. I. Bizyukov, J.W. Davis, A.A. Haasz, P. Brodersen.
CD4 production from mixed W-C-D surface during
simultaneous ir-radiation of W with C+ and D+ // J.
Nucl. Mater. 2009, v. 391, p. 925-928.
8. B.V. Mech, A.A. Haasz, J.W. Davis. Isotopic effects in
hydrocarbon formation due to low-energy H+/D+
impact on graphite // J. Nucl. Mater. 1998, v. 255,
p. 153-164.
9. I. Bizyukov, J.W. Davis, A.A. Haasz, P. Brodersen. C
and D reemission from mixed W-C-D layers during
single-species and simultaneous irradiations of W with
C+ and D+ // J. Nucl. Mater. 2010, v. 400, p. 245-250.
10. V. Philipps, E. Vietzke, R.P. Schorn, H. Trinkaus.
Flux dependence of radiation induced sublimation of
graphite at elevated temperatures // J. Nucl. Mater.
1988, v. 155-157, p. 319-323.
Article received 13.09.10
КЛЮЧЕВЫЕ СВОЙСТВА СМЕШАННОЙ W-C-D ПОВЕРХНОСТИ,
ВЛИЯЮЩИЕ НА ЭРОЗИЮ ВОЛЬФРАМА
И.А. Бизюков
Распыление поверхности вольфрама, облучаемого смешанным потоком частиц углерода и дейтерия, нахо-
дится под влиянием нескольких факторов. Основным фактором является формирование смешанной W-C-D по-
верхности, что уменьшает количество атомов вольфрама в приповерхностной области, откуда они распыляют-
ся. Другие факторы, такие как химическое распыление и радиационно-усиленная сублимация, влияют на кон-
центрацию углерода на поверхности и связаны с ее повышенной температурой.
КЛЮЧОВІ ВЛАСТИВОСТІ ЗМІШАНОЇ W-C-D ПОВЕРХНІ,
ЯКІ ВПЛИВАЮТЬ НА ЕРОЗІЮ ВОЛЬФРАМУ
І.О. Бізюков
Розпилення поверхні вольфраму, опромінюваної змішаним потоком частинок вуглецю й дейтерію,
знаходиться під впливом кількох факторів. Основним фактором є формування змішаної W-C-D поверхні, що
зменшує кількість атомів вольфраму у приповерхневій області, звідкіля вони розпилюються. Інші фактори, такі
як хімічне розпилення та радіаційно-посилена сублімація, впливають на концентрацію вуглецю на поверхні і
пов'язані з її підвищеною температурою.
КЛЮЧЕВЫЕ СВОЙСТВА СМЕШАННОЙ W-C-D ПОВЕРХНОСТИ,
ВЛИЯЮЩИЕ НА ЭРОЗИЮ ВОЛЬФРАМА
КЛЮЧОВІ ВЛАСТИВОСТІ ЗМІШАНОЇ W-C-D ПОВЕРХНІ,
ЯКІ ВПЛИВАЮТЬ НА ЕРОЗІЮ ВОЛЬФРАМУ
|
| id | nasplib_isofts_kiev_ua-123456789-17468 |
| institution | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| issn | 1562-6016 |
| language | English |
| last_indexed | 2025-11-28T14:19:34Z |
| publishDate | 2010 |
| publisher | Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| record_format | dspace |
| spelling | Bizyukov, I.A. 2011-02-26T21:31:44Z 2011-02-26T21:31:44Z 2010 Key properties of mixed W-C-D surface related to tungsten erosion / I.A. Bizyukov // Вопросы атомной науки и техники. — 2010. — № 6. — С. 91-93. — Бібліогр.: 10 назв. — англ. 1562-6016 https://nasplib.isofts.kiev.ua/handle/123456789/17468 The erosion of tungsten exposed to the mixed particle flux of carbon and deuterium ions is effected by several factors. The main factor is the formation of mixed W-C-D surface, which decreases content of tungsten atoms in the near-surface region. Other factors affect carbon content on the surface and attributed to elevated surface temperature: chemical erosion and radiation-enhanced sublimation. Распыление поверхности вольфрама, облучаемого смешанным потоком частиц углерода и дейтерия, находится под влиянием нескольких факторов. Основным фактором является формирование смешанной W-C-D поверхности, что уменьшает количество атомов вольфрама в приповерхностной области, откуда они распыляются. Другие факторы, такие как химическое распыление и радиационно-усиленная сублимация, влияют на концентрацию углерода на поверхности и связаны с ее повышенной температурой. Розпилення поверхні вольфраму, опромінюваної змішаним потоком частинок вуглецю й дейтерію, знаходиться під впливом кількох факторів. Основним фактором є формування змішаної W-C-D поверхні, що зменшує кількість атомів вольфраму у приповерхневій області, звідкіля вони розпилюються. Інші фактори, такі як хімічне розпилення та радіаційно-посилена сублімація, впливають на концентрацію вуглецю на поверхні і пов'язані з її підвищеною температурою. en Національний науковий центр «Харківський фізико-технічний інститут» НАН України Динамика плазмы и взаимодействие плазма – стенка Key properties of mixed W-C-D surface related to tungsten erosion Ключевые свойства смешанной W-C-D поверхности, влияющие на эрозию вольфрама Ключові властивості змішаної W-C-D поверхні, які впливають на ерозію вольфраму Article published earlier |
| spellingShingle | Key properties of mixed W-C-D surface related to tungsten erosion Bizyukov, I.A. Динамика плазмы и взаимодействие плазма – стенка |
| title | Key properties of mixed W-C-D surface related to tungsten erosion |
| title_alt | Ключевые свойства смешанной W-C-D поверхности, влияющие на эрозию вольфрама Ключові властивості змішаної W-C-D поверхні, які впливають на ерозію вольфраму |
| title_full | Key properties of mixed W-C-D surface related to tungsten erosion |
| title_fullStr | Key properties of mixed W-C-D surface related to tungsten erosion |
| title_full_unstemmed | Key properties of mixed W-C-D surface related to tungsten erosion |
| title_short | Key properties of mixed W-C-D surface related to tungsten erosion |
| title_sort | key properties of mixed w-c-d surface related to tungsten erosion |
| topic | Динамика плазмы и взаимодействие плазма – стенка |
| topic_facet | Динамика плазмы и взаимодействие плазма – стенка |
| url | https://nasplib.isofts.kiev.ua/handle/123456789/17468 |
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