HIgh heat flux plasma testing of ITER divertor materials under ELM relevant conditions in QSPA Kh-50
Performed studies of plasma-surface interaction include measurements of plasma energy deposited to the material surface and determination of tungsten cracking threshold during repetitive ITER ELM-like plasma exposures in QSPA Kh-50 with plasma pulses of energy density up to 2.5 MJ/m2 and duration of...
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України
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| Цитувати: | HIgh heat flux plasma testing of ITER divertor materials under ELM relevant conditions in QSPA Kh-50 / V.A. Makhlaj, I.E. Garkusha, N.N. Aksenov, N.V. Kulik, I.S. Landman, J. Linke, A.V. Medvedev, S.V. Malykhin, V.V. Chebotarev, A.T. Pugachev, V.I. Tereshin // Вопросы атомной науки и техники. — 2010. — № 6. — С. 57-59. — Бібліогр.: 8 назв. — англ. |
Репозитарії
Digital Library of Periodicals of National Academy of Sciences of Ukraine| _version_ | 1860089155237707776 |
|---|---|
| author | Makhlaj, V.A. Garkusha, I.E. Aksenov, N.N. Kulik, N.V. Landman, I.S. Linke, J. Medvedev, A.V. Malykhin, S.V. Chebotarev, V.V. Pugachev, A.T. Tereshin, V.I. |
| author_facet | Makhlaj, V.A. Garkusha, I.E. Aksenov, N.N. Kulik, N.V. Landman, I.S. Linke, J. Medvedev, A.V. Malykhin, S.V. Chebotarev, V.V. Pugachev, A.T. Tereshin, V.I. |
| citation_txt | HIgh heat flux plasma testing of ITER divertor materials under ELM relevant conditions in QSPA Kh-50 / V.A. Makhlaj, I.E. Garkusha, N.N. Aksenov, N.V. Kulik, I.S. Landman, J. Linke, A.V. Medvedev, S.V. Malykhin, V.V. Chebotarev, A.T. Pugachev, V.I. Tereshin // Вопросы атомной науки и техники. — 2010. — № 6. — С. 57-59. — Бібліогр.: 8 назв. — англ. |
| collection | DSpace DC |
| description | Performed studies of plasma-surface interaction include measurements of plasma energy deposited to the material surface and determination of tungsten cracking threshold during repetitive ITER ELM-like plasma exposures in QSPA Kh-50 with plasma pulses of energy density up to 2.5 MJ/m2 and duration of 0.25 ms. The energy threshold for tungsten cracking development is found to be ~0,3 MJ/m2. The Ductile-to-Brittle Transition Temperature (DBTT) is experimentally estimated for ITER relevant tungsten grade. Major crack network (cells size up to 1.3 mm) forms only in cases of initial target temperatures below DBTT. Intergranular micro-cracks network (size of cells corresponds to the grain size) appears under heat loads after melting threshold.
|
| first_indexed | 2025-12-07T17:21:42Z |
| format | Article |
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PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY. 2010. 6. 57
Series: Plasma Physics (16), p. 57-59.
HIGH HEAT FLUX PLASMA TESTING OF ITER DIVERTOR MATERIALS
UNDER ELM RELEVANT CONDITIONS IN QSPA Kh-50
V.A. Makhlaj1, I.E. Garkusha1, N.N. Aksenov1, N.V. Kulik1, I.S. Landman2, J. Linke3,
A.V. Medvedev1, S.V. Malykhin4, V.V. Chebotarev1, A.T. Pugachev4, V.I. Tereshin1
1Institute of Plasma Physics NSC “Kharkov Institute of Physics and Technology”, Kharkov, Ukraine;
2Karlsruhe Institute of Technology (KIT), IHM, 76344 Karlsruhe, Germany;
3Forschungszentrum Jülich, IEF 2 D-52425 Juelich, Germany;
4Kharkov Polytechnic Institute, NTU, 61002, Kharkov, Ukraine
E-mail: makhlay@ipp.kharkov.ua
Performed studies of plasma-surface interaction include measurements of plasma energy deposited to the material
surface and determination of tungsten cracking threshold during repetitive ITER ELM-like plasma exposures in QSPA
Kh-50 with plasma pulses of energy density up to 2.5 MJ/m2 and duration of 0.25 ms. The energy threshold for tungsten
cracking development is found to be ~0,3 J/m2. The Ductile-to-Brittle Transition Temperature (DBTT) is
experimentally estimated for ITER relevant tungsten grade. Major crack network (cells size up to 1.3 mm) forms only
in cases of initial target temperatures below DBTT. Intergranular micro-cracks network (size of cells corresponds to the
grain size) appears under heat loads after melting threshold.
PACS: 52.40.Hf
1. INTRODUCTION
Divertor armor response to the repetitive plasma
impacts during the transient events in ITER and DEMO
remains to be one of the most important issues that
determine the tokamak performance. Erosion of plasma-
facing components (PFCs) restricts the divertor lifetime,
leads to contamination of the hot plasma by impurities
and can produce a substantial amount of the material
dust [1]. The present-day experimental investigations of
plasma-surface interaction under conditions simulating
ITER transient events are aimed at determination of
erosion mechanisms of plasma facing materials, dynamics
of erosion products, the impurities transport in the plasma,
the vapor shield effects and its influence on plasma
energy transfer to the material surface [2-8].
This paper presents recent results of ELM-simulation
experiments with the quasi-stationary plasma accelerator
QSPA Kh-50. The experiments include study of plasma-
surface interaction under inclined plasma impact, the
cracks analysis and the results of residual stress
measurements for tungsten targets with elongated grains,
which is ITER reference W grade.
2. EXPERIMENTAL SETUP
AND DIAGNOSTICS
Experimental simulations of ITER ELMs (Edge
Localized Modes) impacts were performed with quasi-
steady-state plasma accelerator QSPA Kh-50 that is
largest and most powerful device of this kind [2, 5-8]. The
main parameters of QSPA Kh-50 hydrogen plasma
streams were as follows: ion impact energy about
0.4 keV, maximum plasma pressure 3.2 bar, and the
plasma stream diameter 18 cm. The plasma pulse shape is
approximately triangular, pulse duration 0.25 ms and the
heat loads varied in the range (0.2…2.5) MJ/m2.
A deformed W grade sample delivered from Plansee
AG, was used for the plasma load tests. Cylindrical shaped
specimens had been a diameter of 12 mm and a height of
5 mm [4]. An electric heater was installed at target’s back-
side to keep the target temperature in the range
T0 = (200…600) °C before plasma pulse. For temperature
monitoring a calibrated thermocouple and an infrared
pyrometer were used. All targets were exposed to
perpendicular plasma stream. The energy density in
plasma stream and surface heat load measured with a
calorimeter.
Surface analysis was carried out with an optical
microscope MMR-4 equipped with a CCD camera and
Scanning Electron Microscopy (SEM) JEOL JSM-6390.
The so called ‘ϑ-2ϑ scans’ with X-ray diffraction
technique (XRD) of exposed targets were performed
using a monochromatic Kα line of Cu anode radiation [7].
Diffraction peaks intensity, their profiles, and their
angular positions were analyzed for estimation the
macrostrain and the lattice parameters.
3. EXPERIMENTAL RESULTS
3.1. FEATURES PLASMA-SURFACE
INTERACTION IN QSPA Kh-50
In our previous experiments it was demonstrated that
tungsten melting threshold under QSPA Kh-50 exposures
is (0.56…0.6) MJ/m2. The evaporation onset is estimated
as 1.1 MJ/m2 [2]. For combined W-C targets the melting
and evaporation was not achieved under the plasma
exposures with fixed energy density. Enhanced
evaporation of carbon (carbon evaporation threshold
(0.4…0.45) MJ/m2) results in additional shielding of
tungsten surface by C cloud. It protects W surface from
the evaporation even for essentially increased energy
density of impacting plasma [6].
Calorimetric measurements demonstrate that even for
plasma exposures, which not result in the tungsten
melting, the absorbed heat load is not more 60% of the
impact plasma energy. The stopped plasma layer, formed
from the head of the plasma stream, ceases to be
completely transparent for subsequently impacting plasma
mailto:makhlay@ipp.kharkov.ua
58
ions [2, 6]. This layer of cold plasma is responsible for
decreasing part of incident plasma energy which is
delivered to the surface. In recent studies for inclined
exposure of the different targets, diminution of energy
density delivered to surface has been observed with
decrease of incidence angle (Fig. 1).
0 30 60 90
W
W+C
C
1.5
1.0
0.5
α
q,
M
J/
m
2
α, degree
0.0
Plasma stream
Fig.1. Heat load to the target surface vs. incidence angle
of impacting plasma stream. Plasma stream energy
density is 2.4 MJ/m2
3.2. CRACKING THRESHOLDS ANALYSIS
Cracking development is characterized by measured
threshold load and threshold target temperature, which
determine the existing region of W performance without
cracks. The energy threshold for tungsten cracking
development is found to be ~0.3 J/m2 for QSPA Kh-50
pulse. The Ductile Brittle Transition Temperature
(DBTT) is experimentally estimated. The Ductile Brittle
Transition (DBT) occurs in the temperature range of
200 ºC TDBTT < 300 º . For initial temperature
T0 > 300 °C no major cracks are formed on the exposed
surface.
Major cracks network forms only in cases of initial
target temperatures below DBTT. Mesh of cells of major
crack network is achieved (0.8…1.3) mm for near the
center of the spot (Fig. 2).
Fig. 2. SEM image of major crack network on tungsten
surface after 5 pulses of 0.45 MJ/m2, T0 = 200 °C
Intergranular micro-cracks appear after plasma
exposition with heat load above melting threshold.
Typical cell sizes of intergranular micro-cracks network
are 10 to 80 µm. Most of cells are within (10…40) µm,
which corresponds to the grain size of this W grade
(Fig. 3). The micro-cracks propagate along the grain
boundaries completely surrounding the grains. The typical
width of intergranular cracks is not exceeded 1 µm. Fine
cracks are developed in rather thin surface layer
~ (5…10) µm. Major cracks are much deeper (Fig. 4).
Appearance of pores in some regions of surface layer can
be caused by expansion of macro-cracks mesh and losses
of tungsten grains in result of plasma impacts.
Fig. 3. SEM image of micro cracks network on tungsten
surface after 5 plasma pulses of 0.75 MJ/m2, T0 = 600 °C
Fig. 4. Cross-section of tungsten target preheated at
T0 = 200 °C and exposed with 10 pulses of 0.75 MJ/m2
3.3. RESIDUAL STRESSES IN TUNGSTEN
AFFECTED BY PLASMA STREAMS
The XRD diffraction analysis has confirmed absence
of material phases built of impurities. Only W lines on the
surface and in deeper layers were observed. This is
important indication of plasma and target purity.
Plasma irradiation results in a symmetrical tensile
stress in thin subsurface layer. Rather weak dependencies
of residual stresses on the initial temperature and the
irradiation dose were obtained for plasma exposures with
heat load of 0.2 MJ/m2. The values of residual
stresses ≈ 160…180) MPa.
The residual stress of 314 MPa appears in the surface
preheated to T0 = 200 °C and exposed by single plasma
pulse of 0.45 MJ/m2. If T0 overcomes the DBTT point the
stress drops down to 250 MPa. Increasing the number of
plasma pulses leads to some saturation of residual stress
which does not depend on T0 (Fig. 5).
Single pulse irradiation of W surface preheated at
200 0C with the heat load above the melting threshold
0.75 MJ/m2 led to the absolute maximal residual stress
390 MPa. Preheating of tungsten at the temperature larger
than 400 0C causes the saturation of the residual stress in
tungsten on the level of 300 MPa. In the course of 5
plasma pulses the residual stress linearly decreases from
59
362 MPa down to 200 MPa with rising of initial surface
temperature from 200 up to 600 0C (see Fig. 5).
0 200 400 600 800
0
100
200
300
400
500 2
1
R
es
id
ua
l s
tr
es
se
s (
M
Pa
)
Temperature (C)
Fig.5. Residual stresses in tungsten targets exposed with
five QSPA plasma pulses of 0.45 MJ/m2 (1) and
0.75 MJ/m2(2) versus the initial bulk temperature
4. CONCLUSIONS
1. Features of tungsten erosion under repetitive plasma
heat loads up to 1.1 MJ/m2 lasting 0.25 ms, which are
relevant to ITER Type I ELMs, has been investigated.
2. Influence of target inclination and neighborhood W and
C as divertor components on the material response to
the repetitive plasma heat loads was analyzed.
3. The energy threshold for cracking development is
found to be ~0.3 J/m2 for plasma pulse of 0.25 ms
duration with triangular pulse shape.
4. The Ductile-to-Brittle Transition occurs in the
temperature range of 200 ºC TDBTT < 300 º . For
initial target temperature T0 > 300 C no major cracks
are formed on the exposed surface.
5. Major cracks network forms only if initial target
temperature is below DBTT. The intergranular micro-
cracks network appears under heat loads above the
melting threshold.
6. Performed measurements demonstrate that the residual
stress does not depend practically on initial target
temperature and it significantly grows with increasing
thermal loads.
This work is supported in part by STCU project
# P405
REFERENCES
1. J. Roth, et al. // Journal of Nuclear Materials. 2009,
v. 390–391, p. 1-9.
2. V.I. Tereshin, et al. // Plasma Physics Controlled
Fusion. 2007, v. 49, p. A231-A239.
3. N. Klimov, et al. // Journal of Nuclear Materials. 2009,
v. 390–391, p. 721–726.
4. T. Hirai, et al. // Journal of Nuclear Materials. 2009,
v. 390–391, p. 751–754.
5. I.E. Garkusha, et al. // Physica Scripta. 2009, v. T138,
014054 (doi:10.1088/0031-8949/2009/T138/014054).
6. I.E. Garkusha, et al. // Journal of Nuclear Materials.
2009, v. 386–388, p. 127-131.
7. V.A. Makhlaj, et al. // Physica Scripta. 2009, v. T138,
014060 (doi: 10.1088/0031-8949/2009/T138/014060).
8. V.A. Makhlay, et al. // Physica Scripta. 2007. v. T128,
p. 239-241.
Article received 29. 10. 2010
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|
| id | nasplib_isofts_kiev_ua-123456789-17458 |
| institution | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| issn | 1562-6016 |
| language | English |
| last_indexed | 2025-12-07T17:21:42Z |
| publishDate | 2010 |
| publisher | Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| record_format | dspace |
| spelling | Makhlaj, V.A. Garkusha, I.E. Aksenov, N.N. Kulik, N.V. Landman, I.S. Linke, J. Medvedev, A.V. Malykhin, S.V. Chebotarev, V.V. Pugachev, A.T. Tereshin, V.I. 2011-02-26T20:57:28Z 2011-02-26T20:57:28Z 2010 HIgh heat flux plasma testing of ITER divertor materials under ELM relevant conditions in QSPA Kh-50 / V.A. Makhlaj, I.E. Garkusha, N.N. Aksenov, N.V. Kulik, I.S. Landman, J. Linke, A.V. Medvedev, S.V. Malykhin, V.V. Chebotarev, A.T. Pugachev, V.I. Tereshin // Вопросы атомной науки и техники. — 2010. — № 6. — С. 57-59. — Бібліогр.: 8 назв. — англ. 1562-6016 https://nasplib.isofts.kiev.ua/handle/123456789/17458 Performed studies of plasma-surface interaction include measurements of plasma energy deposited to the material surface and determination of tungsten cracking threshold during repetitive ITER ELM-like plasma exposures in QSPA Kh-50 with plasma pulses of energy density up to 2.5 MJ/m2 and duration of 0.25 ms. The energy threshold for tungsten cracking development is found to be ~0,3 MJ/m2. The Ductile-to-Brittle Transition Temperature (DBTT) is experimentally estimated for ITER relevant tungsten grade. Major crack network (cells size up to 1.3 mm) forms only in cases of initial target temperatures below DBTT. Intergranular micro-cracks network (size of cells corresponds to the grain size) appears under heat loads after melting threshold. en Національний науковий центр «Харківський фізико-технічний інститут» НАН України ИТЭР и приложения для термоядерного реактора HIgh heat flux plasma testing of ITER divertor materials under ELM relevant conditions in QSPA Kh-50 Тестирование мощными потоками плазмы материалов дивертора ITER в условиях, соответствующих ELM, на КСПУ Х-50 Article published earlier |
| spellingShingle | HIgh heat flux plasma testing of ITER divertor materials under ELM relevant conditions in QSPA Kh-50 Makhlaj, V.A. Garkusha, I.E. Aksenov, N.N. Kulik, N.V. Landman, I.S. Linke, J. Medvedev, A.V. Malykhin, S.V. Chebotarev, V.V. Pugachev, A.T. Tereshin, V.I. ИТЭР и приложения для термоядерного реактора |
| title | HIgh heat flux plasma testing of ITER divertor materials under ELM relevant conditions in QSPA Kh-50 |
| title_alt | Тестирование мощными потоками плазмы материалов дивертора ITER в условиях, соответствующих ELM, на КСПУ Х-50 |
| title_full | HIgh heat flux plasma testing of ITER divertor materials under ELM relevant conditions in QSPA Kh-50 |
| title_fullStr | HIgh heat flux plasma testing of ITER divertor materials under ELM relevant conditions in QSPA Kh-50 |
| title_full_unstemmed | HIgh heat flux plasma testing of ITER divertor materials under ELM relevant conditions in QSPA Kh-50 |
| title_short | HIgh heat flux plasma testing of ITER divertor materials under ELM relevant conditions in QSPA Kh-50 |
| title_sort | high heat flux plasma testing of iter divertor materials under elm relevant conditions in qspa kh-50 |
| topic | ИТЭР и приложения для термоядерного реактора |
| topic_facet | ИТЭР и приложения для термоядерного реактора |
| url | https://nasplib.isofts.kiev.ua/handle/123456789/17458 |
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