Experimental study of plasma-surface interaction and material damage relevant to ITER type i ELMs
The paper presents experimental investigations of main features of plasma-surface interaction and energy transfer
 to the material surface in dependence on plasma heat loads. The experiments were performed with QSPA repetitive
 plasma pulses of the duration of 0.25 ms and the energy...
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| Date: | 2006 |
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України
2006
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| Cite this: | Experimental study of plasma-surface interaction and material damage relevant to ITER type i ELMs / V. A. Makhlaj, A.N. Bandura, O.V. Byrka, V.V. Chebotarev, I.E. Garkusha, V.V. Garkusha, N.V. Kulik, I. Landman, S.I. Lebedev, I.M. Neklyudov, V.V. Staltsov, V.I. Tereshin // Вопросы атомной науки и техники. — 2006. — № 6. — С. 74-76. — Бібліогр.: 8 назв. — англ. |
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Digital Library of Periodicals of National Academy of Sciences of Ukraine| _version_ | 1860254057380184064 |
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| author | Makhlaj, V. A. Bandura, A.N. Byrka, O.V. Chebotarev, V.V. Garkusha, I.E. Garkusha, V.V. Kulik, N.V. Landman, I. Lebedev, S.I. Neklyudov, I.M. Staltsov, V.V. Tereshin, V.I. |
| author_facet | Makhlaj, V. A. Bandura, A.N. Byrka, O.V. Chebotarev, V.V. Garkusha, I.E. Garkusha, V.V. Kulik, N.V. Landman, I. Lebedev, S.I. Neklyudov, I.M. Staltsov, V.V. Tereshin, V.I. |
| citation_txt | Experimental study of plasma-surface interaction and material damage relevant to ITER type i ELMs / V. A. Makhlaj, A.N. Bandura, O.V. Byrka, V.V. Chebotarev, I.E. Garkusha, V.V. Garkusha, N.V. Kulik, I. Landman, S.I. Lebedev, I.M. Neklyudov, V.V. Staltsov, V.I. Tereshin // Вопросы атомной науки и техники. — 2006. — № 6. — С. 74-76. — Бібліогр.: 8 назв. — англ. |
| collection | DSpace DC |
| container_title | Вопросы атомной науки и техники |
| description | The paper presents experimental investigations of main features of plasma-surface interaction and energy transfer
to the material surface in dependence on plasma heat loads. The experiments were performed with QSPA repetitive
plasma pulses of the duration of 0.25 ms and the energy density up to 2.5 MJ/m2
. Surface morphology of the targets
exposed to QSPA plasma screams is analyzed. Relative contribution of the Lorentz force and plasma pressure gradient
to the resulting surface profile is discussed. Development of cracking on the tungsten surface and swelling of the
surface are found to be in strong dependence on initial temperature of the target.
|
| first_indexed | 2025-12-07T18:46:59Z |
| format | Article |
| fulltext |
74 Problems of Atomic Science and Technology. 2006, 6. Series: Plasma Physics (12), p. 74-76
EXPERIMENTAL STUDY OF PLASMA-SURFACE INTERACTION
AND MATERIAL DAMAGE RELEVANT TO ITER TYPE I ELMS
V. A. Makhlaj, A.N. Bandura, O.V. Byrka, V.V. Chebotarev, I.E. Garkusha, V.V. Garkusha,
N.V. Kulik, I. Landman1, S.I. Lebedev, I.M. Neklyudov2, V.V. Staltsov, V.I. Tereshin
Institute of Plasma Physics of the NSC KIPT, Akademicheskaya Str.1, 61108 Kharkov, Ukraine;
1Forschungszentrum Karlsruhe, IHM, 76021 Karlsruhe, Germany;
2NSC Kharkov Institute of Physics and Technology, Akademicheskaya Str.1, 61108 Kharkov, Ukraine
The paper presents experimental investigations of main features of plasma-surface interaction and energy transfer
to the material surface in dependence on plasma heat loads. The experiments were performed with QSPA repetitive
plasma pulses of the duration of 0.25 ms and the energy density up to 2.5 MJ/m2. Surface morphology of the targets
exposed to QSPA plasma screams is analyzed. Relative contribution of the Lorentz force and plasma pressure gradient
to the resulting surface profile is discussed. Development of cracking on the tungsten surface and swelling of the
surface are found to be in strong dependence on initial temperature of the target.
PACS. 52.40.Hf
1. INTRODUCTION
The major part of ITER divertor armor is foreseen to
be made of tungsten and carbon fibre composite (CFC).
Energy loads to ITER divertor surfaces associated with
the Type I Edge Localized Modes (ELMs) are supposed
to be up to Q = 3 MJ/m2 during τ = (0.1…0.5) ms and the
number of ELMs about 103 for one ITER pulse [1].
Quasi-Steady-State Plasma Accelerators (QSPA) well
reproduce the energy densities (Q) and pulse durations (τ)
of ITER ELMs [2, 3]. Experimental investigations of plasma-
surface interaction in ITER relevant conditions are aimed
the determination of main erosion mechanisms for the
divertor armour materials, dynamics of erosion products,
vapor shield effects under plasma heat loads. In turn, the
obtained results are used for validation of predictive
models developed for ITER [4], estimation of tolerable
size of ITER ELMs and lifetime of divertor armour
materials.
The paper describes experimental investigations of
plasma energy transfer to the material surface in
dependence on plasma heat loads. Some results on
electromagnetic force influence on the melt motion of
metals and effect of preheating on the tungsten damage
are presented also.
2. EXPERIMENTAL DEVICE
The samples of different materials (tungsten, copper,
titanium, MPG-7 graphite) have been exposed with
various number of pulses of hydrogen plasma streams
produced by the quasi-steady-state plasma accelerator
QSPA Kh-50, described elsewhere [2]. The experiments were
performed with repetitive pulses of the duration of 0.25 ms
and the energy density in the range of (0.5…2.5) MJ/m2.
The plasma stream diameter is 18 cm, the ion energy is
about 0.4 keV, and maximum plasma pressure achieves
3.2 bar.
Molybdenum diaphragms with different diameter of
holes were used to form narrow central part of plasma
stream, which is impacted on the target surface, and to
create situation when target size exceeds the plasma
stream diameter. Scheme of target irradiation is described
in details in [5]. In some experiments an Ohmic heater
was installed behind the tungsten target to study the
influence of target preheating up to tinit 650 °C on
surface cracking [6, 7].
Contribution of electromagnetic force to the melt layer
erosion of metals was investigated with use of special
magnetic system for creation of magnetic field along the
exposed surface. The maximal external magnetic field of
up to 1.5 T and electric current density of ~1.4 kA/cm2
through the melt layer are achieved [8].
Calorimetry (both at plasma stream and at the target
surface), piezo-detectors, electric and magnetic probes,
Rogowski coils, spectroscopy and other diagnostics were
applied for measurements of plasma parameters and
surface heat loads in different regimes of operation.
3. EXPERIMENTAL RESULTS
3.1. PLASMA ENERGY TRANSFER TO THE
MATERIAL SURFACES
As it was shown earlier in disruption simulation
experiments [2] the main feature of high-power plasma
interaction with material surfaces is dense plasma shield
formation in front of the target surface. The ELM heat
loads is much less than disruption ones, however, some
shielding effect can also appear in this case.
Fig.1. shows the heat loads to the tungsten surface,
which were measured with calorimetry, in dependence on
energy density of impacting plasma stream for 2 cases:
without and with graphite as surrounding surface. For
these studies the combined W-C target was prepared.
Onset of tungsten melting is observed on the target
surface at pulsed heat load of 0.57 MJ/m2.
For tungsten target the vapor shield formation and its
influence on plasma energy transfer to the surface became
clearly seen when the surface heat load achieves 1.1 MJ/m2.
Measurements of heat loads for combined tungsten-
graphite target show that the value of energy density
delivered to the target surface is reduced in comparison
with tungsten irradiation. In this case the carbon vapor
shield formation results in additional decrease of the
surface heat loads up to (0.8…0.85) MJ/m2.
75
The measurements demonstrate that even for plasma
exposures, which not resulted in tungsten melting, the
target heat load is about (55…60) % of the impact plasma
energy. The dynamical screening of the surface from
impacting plasma stream appears in this case probably
due to plasma stream thermalization under the plasma
stream interaction with target surface. The layer of
stopped plasma formed from head part of the plasma
stream becomes not completely transparent for
subsequently impacting plasma ions. However the vapor
shied formation, especially in the case of mutual
neighborhood of carbon and tungsten results in much
more pronounced surface screening and essentially
restricts the energy transfer to the surface.
3.53.02.52.01.50
0
1.00.5
0.4
0.8
1.2
1.6
W
W+C
Su
rf
ac
e
he
at
lo
ad
, M
J/
m
2
Plasma stream energy density, MJ/m2
Fig. 1. Heat load to the target surfaces vs. the energy
density of impacting plasma stream
The fraction of plasma energy, which is absorbed by
the target surface, is rapidly decreased with achieving the
evaporation onset for exposed targets. At this, the value of
heat load to the surface remains practically constant with
further increase of the energy density of impacting plasma
(plateau region in Fig.1).
3.2. EXTERNAL FORCES INFLUENCE ON THE
MELT LAYER EROSION
The main aim of these experiments was analysis of
relative contributions of pressure gradient and the Lorentz
force to the resulting erosion profiles
Irradiation of tungsten samples with repetitive plasma
heat loads above the melting threshold was performed in
conditions of practically constant plasma pressure along
the exposed surface, but with additional action of
electromagnetic force to the melt layer. Force duration was
~150 µs and maximal magnitude was (14…20) MN/m3
(time averaged one was ~10 MN/m3). It is obtained that
Lorentz force causes continuous inclination of the surface
profile in direction of the force. It contribution to the
resulting erosion profile of tungsten is on the level of 2µm
after 20 pulses (Fig. 2a).
Relative influence of the Lorentz force and plasma
pressure gradient can be easily seen on the profile of Ti
target (Fig. 2b), which was exposed through the diaphragm
of 3 cm with the aim to impose the pressure gradient at
the 5 mm edge zone of the melt spot [5, 8]. The ridge of
displaced material with the height of (70…100) µm is arisen
locally at the melt edges due to effect of the plasma pressure
gradient, which is the main driving force for the peripheral
surface regions close to the diaphragm edges.
a
b
Fig.2. Surface profiles of targets exposed with
20 pulses: a – tungsten; b – titanium
It should be pointed out that for left side of Ti profile,
the Lorentz force adds to the melt motion, and for right
side it is directed opposite to the pressure gradient. That is
why, the ridge height for left side of presented profile is
higher. For the same reason the width of the erosion crater
at the right side is larger. The inclination of the profile
central area is completely determined by Lorentz force
action. The displacement of target material according the
of the Lorentz force direction resulted in profile grow up
to 20 µm for 20 pulses. Areas of predominant action of
the plasma pressure gradients and the Lorentz force are
marked in Fig. 2. In the central area of exposed surface
the Lorentz force is dominating. However, for thin edge
regions the value of pressure gradient in 3 times exceeds
the magnitude of Lorentz force.
3.3. INFLUENCE OF TARGET PREHEATING ON
TUNGSTEN EROSION
Plasma exposures of tungsten targets with initial
temperature at RT level resulted in formation of large size
cracks and fine inter-granular cracks on the surface
(Fig. 3). Surface cracking leads to essentially increased
surface roughness of tungsten and swelling of the surface
profile as whole according to initial reference line [6].
Microscopy analysis shows growing width of the cracks
with increased number of exposures.
Fig. 3. Cell of crack mesh on tungsten surface after
exposed of 100 pulses, tinit = RT
57 µm
grad P
5 mm
50 µm
grad P
LorentzF
r
5 mm
5 µm
76
For the preheated target surface, the roughness grows up
very slowly with increase of irradiation dose. Microscopy
studies demonstrate absence of large cracks, while a fine
crack mesh is still developing. Width of intergranular cracks
increases with number of pulses and achieves 0.8…1.5 µm
after 100 pulses. SEM shows development of cellular
structure on the resolidified tungsten surface after plasma
exposures. Cell size is about 300 nm. Blister-like structures
with size up to 100…150 µm are also appear on the surface
after large number of exposures (Fig. 4).
Fig. 4. SEM image of exposed tungsten surface after
100 pulses, tinit =650 ºC
4. CONCLUSIONS
The obtained results can be summarized as follows:
- Onset of vapor shied formation in front of the surface
under the plasma impact is studied. Achievement of
evaporation threshold for exposed targets results in almost
saturation of the surface heat load with further increase of
the plasma energy density. The investigations of mutual
neighborhood of graphite and tungsten showed the
reduction of energy delivered to the tungsten surface. In
spite of high energy density of impact plasma a tungsten
evaporation threshold is not achieved due to the carbon
vapor shield formation.
- Relative contribution of the Lorentz force and plasma
pressure gradient to the resulting surface profile due to the
melt motion is demonstrated.
- Tungsten preheating above DBTT allows suppression
of macrocracks formation on the surface. However, the
mesh of fine intergranular cracks is steel developed.
Taking into account a lot of ELMS during each ITER
pulse, the evolution of fine cracks and surface
morphology requires additional studies with large number
of plasma exposures.
ACKNOWLEDGEMENTS
This work has been supported in part by Ministry of
Education and Science of Ukraine (grant # M/109-2005)
REFERENCES
1. G. Federici et al.// Plasma Phys. Control. Fus. 2003, v.45,
p.1523.
2. V.V.Chebotarev et al. // J. Nucl. Mater. 1996, v.233-237,
p.736.
3. N.I. Arkhipov et al. // J. Nucl. Mater. 2005, v.337-
339, p.684
4. I.S. Landman et al. // J. Nucl. Mater. 2005, v.337-339,
p.761.
5. V.I. Tereshin et al. // J. Nucl. Mater. 2003, v.313-316,
p.686.
6. I.E. Garkusha et al. // J. Nucl. Mater. 2005, v.337-339,
p.707.
7. V.A. Makhlaj et al. // Proc.11th Int. Works. on Plas.-
Facing Mater. and Comp. for Fus. Appl., Germany.
2006, C-5.
8. I.E. Garkusha et al. // Proc. 17th Int. Conf. on Plas.–
Surf. Inter., China. 2006, P2-4.
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|
| id | nasplib_isofts_kiev_ua-123456789-81786 |
| institution | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| issn | 1562-6016 |
| language | English |
| last_indexed | 2025-12-07T18:46:59Z |
| publishDate | 2006 |
| publisher | Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| record_format | dspace |
| spelling | Makhlaj, V. A. Bandura, A.N. Byrka, O.V. Chebotarev, V.V. Garkusha, I.E. Garkusha, V.V. Kulik, N.V. Landman, I. Lebedev, S.I. Neklyudov, I.M. Staltsov, V.V. Tereshin, V.I. 2015-05-20T16:17:53Z 2015-05-20T16:17:53Z 2006 Experimental study of plasma-surface interaction and material damage relevant to ITER type i ELMs / V. A. Makhlaj, A.N. Bandura, O.V. Byrka, V.V. Chebotarev, I.E. Garkusha, V.V. Garkusha, N.V. Kulik, I. Landman, S.I. Lebedev, I.M. Neklyudov, V.V. Staltsov, V.I. Tereshin // Вопросы атомной науки и техники. — 2006. — № 6. — С. 74-76. — Бібліогр.: 8 назв. — англ. 1562-6016 PACS. 52.40.Hf https://nasplib.isofts.kiev.ua/handle/123456789/81786 The paper presents experimental investigations of main features of plasma-surface interaction and energy transfer
 to the material surface in dependence on plasma heat loads. The experiments were performed with QSPA repetitive
 plasma pulses of the duration of 0.25 ms and the energy density up to 2.5 MJ/m2
 . Surface morphology of the targets
 exposed to QSPA plasma screams is analyzed. Relative contribution of the Lorentz force and plasma pressure gradient
 to the resulting surface profile is discussed. Development of cracking on the tungsten surface and swelling of the
 surface are found to be in strong dependence on initial temperature of the target. This work has been supported in part by Ministry of
 Education and Science of Ukraine (grant # M/109-2005) en Національний науковий центр «Харківський фізико-технічний інститут» НАН України Вопросы атомной науки и техники ITER and fusion reactor aspects Experimental study of plasma-surface interaction and material damage relevant to ITER type i ELMs Article published earlier |
| spellingShingle | Experimental study of plasma-surface interaction and material damage relevant to ITER type i ELMs Makhlaj, V. A. Bandura, A.N. Byrka, O.V. Chebotarev, V.V. Garkusha, I.E. Garkusha, V.V. Kulik, N.V. Landman, I. Lebedev, S.I. Neklyudov, I.M. Staltsov, V.V. Tereshin, V.I. ITER and fusion reactor aspects |
| title | Experimental study of plasma-surface interaction and material damage relevant to ITER type i ELMs |
| title_full | Experimental study of plasma-surface interaction and material damage relevant to ITER type i ELMs |
| title_fullStr | Experimental study of plasma-surface interaction and material damage relevant to ITER type i ELMs |
| title_full_unstemmed | Experimental study of plasma-surface interaction and material damage relevant to ITER type i ELMs |
| title_short | Experimental study of plasma-surface interaction and material damage relevant to ITER type i ELMs |
| title_sort | experimental study of plasma-surface interaction and material damage relevant to iter type i elms |
| topic | ITER and fusion reactor aspects |
| topic_facet | ITER and fusion reactor aspects |
| url | https://nasplib.isofts.kiev.ua/handle/123456789/81786 |
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