Castellated structures behaviour under QSPA Kh-50 plasma exposures in ITER relevant conditions
The experimental study of castellated target erosion under relevant to ITER ELMs surface heat load (i.e., energy density and the pulse duration as well as particle loads) was performed in QSPA Kh-50 quasi-stationary plasma accelerator. The damage of surface, mechanisms of solid/liquid particle eject...
Збережено в:
| Опубліковано в: : | Вопросы атомной науки и техники |
|---|---|
| Дата: | 2014 |
| Автори: | , , , , , , , , , |
| Формат: | Стаття |
| Мова: | English |
| Опубліковано: |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України
2014
|
| Теми: | |
| Онлайн доступ: | https://nasplib.isofts.kiev.ua/handle/123456789/81193 |
| Теги: |
Додати тег
Немає тегів, Будьте першим, хто поставить тег для цього запису!
|
| Назва журналу: | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| Цитувати: | Castellated structures behaviour under QSPA Kh-50 plasma exposures in ITER relevant conditions / S.S. Herashchenko, V.A. Makhlaj, N.N. Aksenov, B. Bazylev, O.V. Byrka, V.V. Chebotarev, N.V. Kulik, S.I. Lebedev, P.B. Shevchuk, V.V. Staltsov // Вопросы атомной науки и техники. — 2014. — № 6. — С. 44-47. — Бібліогр.: 16 назв. — англ. |
Репозитарії
Digital Library of Periodicals of National Academy of Sciences of Ukraine| id |
nasplib_isofts_kiev_ua-123456789-81193 |
|---|---|
| record_format |
dspace |
| spelling |
Herashchenko, S.S. Makhlaj, V.A. Aksenov, N.N. Bazylev, B. Byrka, O.V. Chebotarev, V.V. Kulik, N.V. Lebedev, S.I. Shevchuk, P.B. Staltsov, V.V. 2015-05-13T15:18:20Z 2015-05-13T15:18:20Z 2014 Castellated structures behaviour under QSPA Kh-50 plasma exposures in ITER relevant conditions / S.S. Herashchenko, V.A. Makhlaj, N.N. Aksenov, B. Bazylev, O.V. Byrka, V.V. Chebotarev, N.V. Kulik, S.I. Lebedev, P.B. Shevchuk, V.V. Staltsov // Вопросы атомной науки и техники. — 2014. — № 6. — С. 44-47. — Бібліогр.: 16 назв. — англ. 1562-6016 PACS: 52.40.HF https://nasplib.isofts.kiev.ua/handle/123456789/81193 The experimental study of castellated target erosion under relevant to ITER ELMs surface heat load (i.e., energy density and the pulse duration as well as particle loads) was performed in QSPA Kh-50 quasi-stationary plasma accelerator. The damage of surface, mechanisms of solid/liquid particle ejection for different parts of castellated targets exposed to QSPA plasma streams has been studied in the course of increasing number of pulses. It is shown that melt dynamics at the structure edges, droplet splashing and molten bridges through the slits are determining processes in macroscopic erosion of castellated surface structures. На квазистационарном плазменном ускорителе КСПУ Х-50 проведено экспериментальное изучение эрозии зубчатых мишеней под воздействием поверхностных тепловых (удельная энергия и длительность импульса) и корпускулярных нагрузок, характерных для режимов ELM в ИТЭР. Повреждение поверхности, механизмы эжекции частиц в твердой и капельной фазе из различных частей мишени исследованы в зависимости от количества плазменных импульсов. Показано, что динамика движения расплава на границах структур, разбрызгивание капель и появление «мостиков» расплава через зазоры между составляющими мишени являются определяющими процессами в макроскопической эрозии составных поверхностных структур. На квазістаціонарному плазмовому прискорювачі КСПП Х-50 проведено експериментальне вивчення ерозії зубчастих мішеней під впливом поверхневих теплових (питома енергія і тривалість імпульсу) і корпускулярних навантажень, характерних для режимів ELM в ІТЕР. Пошкодження поверхні, механізми ежекції частинок в твердій і крапельній фазі з різних частин мішені досліджені в залежності від кількості плазмових імпульсів. Показано, що динаміка руху розплаву на межах структур, розбризкування крапель і поява «містків» розплаву через зазори між складовими мішені є визначальними процесами в макроскопічній ерозії складених поверхневих структур. This work is supported in part by National Academy Science of Ukraine project П-5/24-2014 and IAEA’s CRP F1.30.13 en Національний науковий центр «Харківський фізико-технічний інститут» НАН України Вопросы атомной науки и техники ИТЭР и приложения для термоядерного реактора Castellated structures behaviour under QSPA Kh-50 plasma exposures in ITER relevant conditions Поведение зубчатых структур под облучением плазмой КСПУ Х-50 в условиях, характерных для ИТЭР Поведінка зубчастих структур під опроміненням плазмою КСПП Х-50 в умовах, характерних для ITEР Article published earlier |
| institution |
Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| collection |
DSpace DC |
| title |
Castellated structures behaviour under QSPA Kh-50 plasma exposures in ITER relevant conditions |
| spellingShingle |
Castellated structures behaviour under QSPA Kh-50 plasma exposures in ITER relevant conditions Herashchenko, S.S. Makhlaj, V.A. Aksenov, N.N. Bazylev, B. Byrka, O.V. Chebotarev, V.V. Kulik, N.V. Lebedev, S.I. Shevchuk, P.B. Staltsov, V.V. ИТЭР и приложения для термоядерного реактора |
| title_short |
Castellated structures behaviour under QSPA Kh-50 plasma exposures in ITER relevant conditions |
| title_full |
Castellated structures behaviour under QSPA Kh-50 plasma exposures in ITER relevant conditions |
| title_fullStr |
Castellated structures behaviour under QSPA Kh-50 plasma exposures in ITER relevant conditions |
| title_full_unstemmed |
Castellated structures behaviour under QSPA Kh-50 plasma exposures in ITER relevant conditions |
| title_sort |
castellated structures behaviour under qspa kh-50 plasma exposures in iter relevant conditions |
| author |
Herashchenko, S.S. Makhlaj, V.A. Aksenov, N.N. Bazylev, B. Byrka, O.V. Chebotarev, V.V. Kulik, N.V. Lebedev, S.I. Shevchuk, P.B. Staltsov, V.V. |
| author_facet |
Herashchenko, S.S. Makhlaj, V.A. Aksenov, N.N. Bazylev, B. Byrka, O.V. Chebotarev, V.V. Kulik, N.V. Lebedev, S.I. Shevchuk, P.B. Staltsov, V.V. |
| topic |
ИТЭР и приложения для термоядерного реактора |
| topic_facet |
ИТЭР и приложения для термоядерного реактора |
| publishDate |
2014 |
| language |
English |
| container_title |
Вопросы атомной науки и техники |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| format |
Article |
| title_alt |
Поведение зубчатых структур под облучением плазмой КСПУ Х-50 в условиях, характерных для ИТЭР Поведінка зубчастих структур під опроміненням плазмою КСПП Х-50 в умовах, характерних для ITEР |
| description |
The experimental study of castellated target erosion under relevant to ITER ELMs surface heat load (i.e., energy density and the pulse duration as well as particle loads) was performed in QSPA Kh-50 quasi-stationary plasma accelerator. The damage of surface, mechanisms of solid/liquid particle ejection for different parts of castellated targets exposed to QSPA plasma streams has been studied in the course of increasing number of pulses. It is shown that melt dynamics at the structure edges, droplet splashing and molten bridges through the slits are determining processes in macroscopic erosion of castellated surface structures.
На квазистационарном плазменном ускорителе КСПУ Х-50 проведено экспериментальное изучение эрозии зубчатых мишеней под воздействием поверхностных тепловых (удельная энергия и длительность импульса) и корпускулярных нагрузок, характерных для режимов ELM в ИТЭР. Повреждение поверхности, механизмы эжекции частиц в твердой и капельной фазе из различных частей мишени исследованы в зависимости от количества плазменных импульсов. Показано, что динамика движения расплава на границах структур, разбрызгивание капель и появление «мостиков» расплава через зазоры между составляющими мишени являются определяющими процессами в макроскопической эрозии составных поверхностных структур.
На квазістаціонарному плазмовому прискорювачі КСПП Х-50 проведено експериментальне вивчення ерозії зубчастих мішеней під впливом поверхневих теплових (питома енергія і тривалість імпульсу) і корпускулярних навантажень, характерних для режимів ELM в ІТЕР. Пошкодження поверхні, механізми ежекції частинок в твердій і крапельній фазі з різних частин мішені досліджені в залежності від кількості плазмових імпульсів. Показано, що динаміка руху розплаву на межах структур, розбризкування крапель і поява «містків» розплаву через зазори між складовими мішені є визначальними процесами в макроскопічній ерозії складених поверхневих структур.
|
| issn |
1562-6016 |
| url |
https://nasplib.isofts.kiev.ua/handle/123456789/81193 |
| citation_txt |
Castellated structures behaviour under QSPA Kh-50 plasma exposures in ITER relevant conditions / S.S. Herashchenko, V.A. Makhlaj, N.N. Aksenov, B. Bazylev, O.V. Byrka, V.V. Chebotarev, N.V. Kulik, S.I. Lebedev, P.B. Shevchuk, V.V. Staltsov // Вопросы атомной науки и техники. — 2014. — № 6. — С. 44-47. — Бібліогр.: 16 назв. — англ. |
| work_keys_str_mv |
AT herashchenkoss castellatedstructuresbehaviourunderqspakh50plasmaexposuresiniterrelevantconditions AT makhlajva castellatedstructuresbehaviourunderqspakh50plasmaexposuresiniterrelevantconditions AT aksenovnn castellatedstructuresbehaviourunderqspakh50plasmaexposuresiniterrelevantconditions AT bazylevb castellatedstructuresbehaviourunderqspakh50plasmaexposuresiniterrelevantconditions AT byrkaov castellatedstructuresbehaviourunderqspakh50plasmaexposuresiniterrelevantconditions AT chebotarevvv castellatedstructuresbehaviourunderqspakh50plasmaexposuresiniterrelevantconditions AT kuliknv castellatedstructuresbehaviourunderqspakh50plasmaexposuresiniterrelevantconditions AT lebedevsi castellatedstructuresbehaviourunderqspakh50plasmaexposuresiniterrelevantconditions AT shevchukpb castellatedstructuresbehaviourunderqspakh50plasmaexposuresiniterrelevantconditions AT staltsovvv castellatedstructuresbehaviourunderqspakh50plasmaexposuresiniterrelevantconditions AT herashchenkoss povedeniezubčatyhstrukturpodoblučeniemplazmoikspuh50vusloviâhharakternyhdlâitér AT makhlajva povedeniezubčatyhstrukturpodoblučeniemplazmoikspuh50vusloviâhharakternyhdlâitér AT aksenovnn povedeniezubčatyhstrukturpodoblučeniemplazmoikspuh50vusloviâhharakternyhdlâitér AT bazylevb povedeniezubčatyhstrukturpodoblučeniemplazmoikspuh50vusloviâhharakternyhdlâitér AT byrkaov povedeniezubčatyhstrukturpodoblučeniemplazmoikspuh50vusloviâhharakternyhdlâitér AT chebotarevvv povedeniezubčatyhstrukturpodoblučeniemplazmoikspuh50vusloviâhharakternyhdlâitér AT kuliknv povedeniezubčatyhstrukturpodoblučeniemplazmoikspuh50vusloviâhharakternyhdlâitér AT lebedevsi povedeniezubčatyhstrukturpodoblučeniemplazmoikspuh50vusloviâhharakternyhdlâitér AT shevchukpb povedeniezubčatyhstrukturpodoblučeniemplazmoikspuh50vusloviâhharakternyhdlâitér AT staltsovvv povedeniezubčatyhstrukturpodoblučeniemplazmoikspuh50vusloviâhharakternyhdlâitér AT herashchenkoss povedínkazubčastihstrukturpídopromínennâmplazmoûkspph50vumovahharakternihdlâiter AT makhlajva povedínkazubčastihstrukturpídopromínennâmplazmoûkspph50vumovahharakternihdlâiter AT aksenovnn povedínkazubčastihstrukturpídopromínennâmplazmoûkspph50vumovahharakternihdlâiter AT bazylevb povedínkazubčastihstrukturpídopromínennâmplazmoûkspph50vumovahharakternihdlâiter AT byrkaov povedínkazubčastihstrukturpídopromínennâmplazmoûkspph50vumovahharakternihdlâiter AT chebotarevvv povedínkazubčastihstrukturpídopromínennâmplazmoûkspph50vumovahharakternihdlâiter AT kuliknv povedínkazubčastihstrukturpídopromínennâmplazmoûkspph50vumovahharakternihdlâiter AT lebedevsi povedínkazubčastihstrukturpídopromínennâmplazmoûkspph50vumovahharakternihdlâiter AT shevchukpb povedínkazubčastihstrukturpídopromínennâmplazmoûkspph50vumovahharakternihdlâiter AT staltsovvv povedínkazubčastihstrukturpídopromínennâmplazmoûkspph50vumovahharakternihdlâiter |
| first_indexed |
2025-11-24T11:37:30Z |
| last_indexed |
2025-11-24T11:37:30Z |
| _version_ |
1850845422298333184 |
| fulltext |
ITER AND FUSION REACTOR ASPECTS
ISSN 1562-6016. ВАНТ. 2014. №6(94)
44 PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY. 2014, №6. Series: Plasma Physics (20), p. 44-47.
CASTELLATED STRUCTURES BEHAVIOUR UNDER QSPA Kh-50
PLASMA EXPOSURES IN ITER RELEVANT CONDITIONS
S.S. Herashchenko
1
, V.A. Makhlaj
1
, N.N. Aksenov
1
, B. Bazylev
2
, O.V. Byrka
1
,
V.V. Chebotarev
1
, N.V. Kulik
1
, S.I. Lebedev
1
, P.B. Shevchuk
1
, V.V. Staltsov
1
1
Institute of Plasma Physics NSC “Kharkov Institute of Physics and Technology”, Kharkov, Ukraine;
2
Karlsruhe Institute of Technology (KIT), IHM, Karlsruhe, Germany
E-mail: makhlay@ipp.kharkov.ua
The experimental study of castellated target erosion under relevant to ITER ELMs surface heat load (i.e., energy
density and the pulse duration as well as particle loads) was performed in QSPA Kh-50 quasi-stationary plasma
accelerator. The damage of surface, mechanisms of solid/liquid particle ejection for different parts of castellated
targets exposed to QSPA plasma streams has been studied in the course of increasing number of pulses. It is shown
that melt dynamics at the structure edges, droplet splashing and molten bridges through the slits are determining
processes in macroscopic erosion of castellated surface structures.
PACS: 52.40.HF
INTRODUCTION
Tungsten is approved plasma facing material for ITER
divertor because of the low sputtering rate, the high
melting point and low retention of hydrogen isotopes.
However divertor surface will be subjected to extremely
high plasma heat loads during disruptions and Edges
Localized Modes (ELMs) [1].
Some powerful test facilities are available to provide
examinations of plasma-facing materials under transient
ITER-like loads. Impact of ITER-relevant loads upon
material surfaces are now simulated with powerful
pulsed plasma guns and quasi-stationary plasma
accelerators (QSPA) [2, 3], linear plasma-surface
interaction (PSI) devices [4], e-beam facilities [5]. Plasma-
surface interactions during transient events in ITER are
also comprehensively studied with the use of the predictive
numerical codes validated by experimental results obtained
in different simulators [6-11].
Plasma heat load leads to creation of molten layer on
exposed surfaces. The development of perturbations
under the influence of different external forces and
instabilities in the melt layer causes a large macroscopic
erosion of the targets.
Recent results from QSPA simulations demonstrate
that droplets are emitted during the plasma exposure of
tungsten, and dust generation dominates after the end of
plasma pulse, at the time of the following material
cooling [12]. Droplets are emitted in the course of
Kelvin-Helmholtz instability. A decrease of the droplet
velocity with increasing surface heat load is observed.
This decrease could be attributed to the growing size of
the droplets for higher energy loads. Resolidification of
target surface is accompanied by dust ejection driven by
the cracking process [10-12].
The segmentation of divertor targets (castellation)
allows mitigation of induced currents in metal surfaces
during the reactor operation. The reduction of tungsten
damage expected also due to minimization of the
thermal stresses that is mitigation cracking of affected
tungsten surface. Nevertheless, presence of sharp edges
in castellated structure may lead to their enhanced
erosion. The available edges will influence on energy
load distribution. They would provoke the melting
effects on the exposed divertor targets. Therefore,
features of the erosion of castellated targets need to be
comprehensively studied in ITER ELM-like simulation
experiments.
Paper presents results of studies the damage of
castellated targets in simulation experiments with ITER
relevant conditions. Measurements of heat loads to
different parts of castellated target have been also
carried out.
1. EXPERIMENTAL DEVICE AND
DIAGNOSTICS
The quasi-stationary plasma accelerator QSPA Kh-
50 is the largest and most powerful device of this kind
[13-15]. The main parameters of QSPA Kh-50 plasma
streams are as follows: ion impact energy was about
(0.4…0.6) keV, the maximum plasma pressure up to
0.32 MPa, and the stream diameter of 18 cm. The
plasma pulse shape is approximately triangular, and the
pulse duration of 0.25 ms.
The energy density in free plasma and surface heat
load were measured by the local calorimeters. The
plasma pressure was measured by piezoelectric
detectors. Observations of plasma interactions with
exposed surfaces, the dust particle dynamics and the
droplets monitoring are performed with a high-speed 10
bit CMOS pco.1200 s digital camera PCO AG
(exposure time from 1 µs to 1 ms, spectral range from
290 to 1100 nm).
Surface analysis of exposed samples was carried out
with an optical microscope MMR-4, equipped with CCD
camera. Weight loss measurements were also performed.
Two kinds of targets were used in experiments. The
targets design is shown in the Fig. 1. The tungsten
castellated target consists of nine cylinders with
diameter of 5 mm, height of 2 cm and minimal gap
between the cylinders – 1 mm.
Because of tungsten melt is quite viscous, heavy and
also due to the necessity of larger loads to achieve W
melting in some appropriate surface layer, other material
ISSN 1562-6016. ВАНТ. 2014. №6(94) 45
could be used for simulation of key dynamical effects on
the castellated targets. Titanium material with well-known
physical properties has been chosen to enhance the
dynamics of the melt and to achieve the recognizable and
measurable effects for smaller number of plasma pulses as
well as to make clear the analysis of different possible
mechanisms of the surface relief development. The
titanium castellated target consists of nine cubes with
size of 1 cm, the width of the gaps between the cubes
1 mm.
a b
Fig. 1. General view of titanium (a) and tungsten (b)
castellated structures
Targets were exposed to perpendicular and inclined
(inclination angle from parallel to surface incidence is
30º) plasma irradiation with various numbers of pulses.
2. EXPERIMENTAL RESULTS
2.1. THE SURFACE HEAT LOAD ON THE
COMPOUND TARGET
For accurate measurements of the energy density
delivered to different areas of the composite target
surface a special target has been prepared, which is a set
of coaxial cylinders of different diameters. Scheme of
the target is presented in Fig. 2. The smallest diameter
of 4 cm had the cylinder 1. Diameter of the cylinder 2
was 5.5 cm, height all these cylinders was equal 1 cm.
Cylinder 3 with diameter of 7.1 cm and a height of 3 cm
was used as the basis for the entire target structure.
Fig. 2. Scheme of the target with installed calorimeters
and direction of plasma impact
To measure the energy density delivered to the
surface of the target three calorimeters were used in
different places of the target. First calorimeter was
located in the center of the front surface of the first
cylinder. Second – was installed into a lateral surface of
the cylinder 1, as it is shown see in Fig. 2. The distance
from the front surface to this calorimeter was 6 mm.
Third – was placed in the extended front surface area of
the second cylinder at the distance of 2.4 cm from the
center of the target. The measurements have been
performed under 90° and 30° to incident plasma stream.
Those targets were also exposed to perpendicular and
inclined plasma irradiation.
For the front calorimeter (number 1) the vapor
shielding of the surface begins to appear at an energy
density in the incident flow above 1.5 MJ/m
2
under
perpendicular irradiation (Fig. 3,a). It corresponds to the
saturation of the dependence curve and indicates the
evaporation influence on the energy transfer processes.
With increasing energy of the incident plasma stream
above 1 MJ/m
2
the energy value, which recorded by
calorimeter installed to the lateral surface
(calorimeter 2) saturates and it does not exceed
0.1 MJ/m
2
. This value is at least 7.5 times less than the
energy coming to the frontal surface at the maximal
specific energy in the impacting plasma stream. The
behavior of value of heat load registered by
calorimeter 3 is same as for calorimeter 1. The
difference between the values of heat load reaching the
different parts of the combined target is due to the
formation of the plasma shielding layer.
a
b
Fig. 3. Heat load to different parts of the target
surface vs. energy density in plasma stream ( a – for
perpendicular target, b – for inclined target)
For inclined irradiation, thickness of the shielding
layer is smallest at the upper edge of the sample. This
layer of cold plasma is responsible for decreasing part
of incident plasma energy which is delivered to the
surface (Fig. 3,b). First of all, it is concern of value of
heat load received with calorimeter 1 and 3. The value
of heat load measured by calorimeter 2 is at least 5
times larger than the energy measured for perpendicular
target. In such case calorimeter is situated closer to
incoming plasma than under perpendicular irradiation.
2.2. EROSION OF THE TITANIUM
CASTELLATED TARGETS
Interaction of plasma streams with heat load of
0.75 MJ/m
2
and perpendicular titanium surface is
46 ISSN 1562-6016. ВАНТ. 2014. №6(94)
accompanied by melting of exposed surfaces. Melt
motion of material targets caused formation of so-called
bridges, partly filling of the gaps between the structure
units. The particle ejection due to bridge destruction and
growing of instabilities on the edges of the target units
are also observed (Fig. 4,a).
a b
Fig. 4. Exposed surfaces after normal plasma impacts.
Heat loads q=0.75 MJ/m
2
(a) and 0.9 MJ/m
2
(b)
With future increasing of heat loads and irradiation
dose the ripple structure appear on exposed surfaces.
More intensive melt motion, droplet ejection from the
edges of the structure are registered for target irradiated
by plasma with energy density of 0.9 MJ/m
2
(Fig. 4,b).
The first particles splash from the surface practically
(not more 50 s) at once beginning plasma-surface
interaction. The largest number of particle ejects from
the exposed surface before 0.2 ms. Maximum of
droplets velocities is 22 m/s.
For inclined target, the main part of energy density
of incident plasma stream delivers to the top of target.
The edges of cubes are melted and molten material
displaces under by the action of pressure gradient of
incident plasma stream with heat load of 0.75 MJ/m
2
.
As result, the mountains of resolidified material appear.
The melt motion leads to the formation of the bridges
between the edges of the structure units (Fig. 5,a). The
bridges may break away with the next plasma pulses.
Droplet ejection is observed mainly from top region of
target. Development of instabilities in the molten layer
causes droplets splashing. The droplets fly towards the
plasma stream. It may indicate the predominance of
Kelvin-Helmholtz instability [9, 12]. At the same time,
other instabilities develop in the melt layer on the external
edges of the target. It should be mention, that the melt
losses due to such instabilities are negligible.
a b
Fig. 5. Exposed surfaces of inclined target for impacting
heat loads q=0.75 MJ/m
2
(a) and 0.9 MJ/m
2
(b)
The more intensive melt motion on the surface target
is observed under plasma irradiation with the energy
density up to 0.9 MJ/m
2
. The melt motion leads to
filling of the gaps between the units of target by molten
metal and appearance of the ripple structure in the
affected surface layer (Fig. 5,b). The main mechanisms
of particle ejection are separation of the liquid metal
from the solid surface (the Taylor criterion) and the
Rayleigh Taylor instability [9].
Under inclined irradiation the particle start-up time
from the exposed surface is in range of (0.1…1) ms from
the beginning of the plasma-surface interaction. The
difference between the particle start-up times from the
exposed surfaces for perpendicularly and inclined can be
explained by formation of non-uniform vapor shield.
2.3. EROSION OF THE TUNGSTEN
CASTELLATED TARGET
Castellated tungsten target was irradiated with
energy density of 0.9 MJ/m
2
. The maximum number of
plasma impacts – 100 pulses. The plasma pulses of such
energy density caused pronounced melting of target
surface. The ripple structures and cracks developed on
resolidified tungsten surface (Fig. 6).
The micro-crack network is attributed to melting and
following re-solidification [3, 13]. Under the action of
next pulses the major cracks are partly filled by molten
metal. The edges of cylinders are melted and the
mountains of displaced material are formed by the
action of pressure gradient with increasing of number of
plasma pulses.
The large number of ejected particles flies away the
target surface after 0.2 ms from the beginning of plasma
surface interaction (Fig. 7). Therefore, considerable
number of particles ejected in solid state [10, 12, 16].
They may break off from the crack edges during plasma
impact.
a b
Fig. 6. Exposed surface of tungsten cylinder after 20 (a)
and 100 (b) plasma impacts
The major cracks with average network size of
0.8 mm are formed due to the Ductile-to-Brittle
Transition effects [3, 10]. In additional, there are particles
which ejected from liquid surface [10-12]. They have
smaller velocities and start-up time. It indicates the
growing of instabilities on the edges of construction units.
Velocity of tungsten particles was up to 20 m/s (see Fig. 7).
CONCLUSIONS
The experimental study of castellated target erosion
under ITER ELM-like surface heat loads was performed
in QSPA Kh-50 quasi-stationary plasma accelerator.
The experiments were carried out with energy density in
plasma stream of 0.9 MJ/m
2
and pulse duration of
0.25 ms. Such heat load leads to severe melting of
titanium and tungsten targets. The melt layer moves by
the action of pressure gradient of the incident plasma
stream. As result, the bridges through the gaps between
structure units and mountains of re-solidified displaced
ISSN 1562-6016. ВАНТ. 2014. №6(94) 47
material are appear. Droplet ejection is registered from
those target areas. The gaps are covered by molten
metal after a large number of plasma pulses and droplet
ejection decreased.
Fig. 7. Velocity distribution of ejected particles vs.
particle start-up time from the exposed tungsten surface
after 20 pulses. t=0 corresponds to beginning of
plasma-surface interaction
The major cracks and micro cracks were observed
on exposed tungsten surface. With increasing number of
plasma pulses the major cracks are partly filled by
molten metal. The solid particles brake away from the
crack edges during the plasma impact. The droplet
ejection was predominantly from the edges of
castellated structures. Mountains of displaced material
on the edges of constructional units are found to be a
source of the splashed droplets.
Thus, it is shown that melt dynamics on the structure
edges, droplet splashing and molten bridges through the
slits are determining processes in macroscopic erosion
of castellated surface structures.
This work is supported in part by National Academy
Science of Ukraine project П-5/24-2014 and
IAEA’s CRP F1.30.13
REFERENCES
1. R.A. Pitts et al. // J. Nucl. Mater. 2013, v. 438, p. S48.
2. I.E. Garkusha et al. // Phys. Scr. 2009, v. T138, p. 014054.
3. V.A. Makhlaj et al. // Phys. Scr. 2014, v. T161,
p. 014040.
4. G.De. Temmerman et al. // Nucl. Fusion. 2013, v. 53,
p. 023008.
5. Th. Loewenhoff et al. // Phys. Scr. 2011, v. T145,
p. 014057.
6. V.A. Makhlaj et al. // Problems of Atomic Science
and Technology. 2013, № 1.
7. V.A. Makhlaj et al. // Phys. Scr. 2011, v. T145,
p. 014061.
8. G. Miloshevsky et al. // J. Nucl. Mater. 2011, v. 415, № 1,
p. S74.
9. I.S. Landman et al. // Phys. Scr. 2004, № T111,
p. 212.
10. S. Pestchanyi et al. // Fusion Eng. and Design. 2010,
v. 85, p. 1697.
11. S. Pestchanyi et al. // Fusion Science and
Technology. 2014, v. 66, p. 150.
12. I.E. Garkusha et al. // Fusion Science and
Technology. 2014, v. 65, p. 186.
13. V.V. Chebotarev et al. // J. Nucl. Mater. 1996,
v. 233-237, p. 736.
14. V.I. Tereshin et al. // Plasma Phys. Control. Fusion.
2007, v. 49, p. A231.
15. I.E Garkusha et al. // J. Nucl. Mater. 2011, v. 415, p. 65.
16. V.A. Makhlaj et al. // J. Nucl. Mater. 2013, v. 438, p. S233.
Article received 10.11.2014
ПОВЕДЕНИЕ ЗУБЧАТЫХ СТРУКТУР ПОД ОБЛУЧЕНИЕМ ПЛАЗМОЙ КСПУ Х-50 В УСЛОВИЯХ,
ХАРАКТЕРНЫХ ДЛЯ ИТЭР
С.С. Геращенко, В.А. Махлай, Н.Н. Аксенов, Б. Базылев, О.В. Бырка, В.В. Чеботарев,
Н.В. Кулик, С.И. Лебедев, П.Б. Шевчук, В.В. Стальцов
На квазистационарном плазменном ускорителе КСПУ Х-50 проведено экспериментальное изучение эрозии
зубчатых мишеней под воздействием поверхностных тепловых (удельная энергия и длительность импульса) и
корпускулярных нагрузок, характерных для режимов ELM в ИТЭР. Повреждение поверхности, механизмы
эжекции частиц в твердой и капельной фазе из различных частей мишени исследованы в зависимости от
количества плазменных импульсов. Показано, что динамика движения расплава на границах структур,
разбрызгивание капель и появление «мостиков» расплава через зазоры между составляющими мишени являются
определяющими процессами в макроскопической эрозии составных поверхностных структур.
ПОВЕДІНКА ЗУБЧАСТИХ СТРУКТУР ПІД ОПРОМІНЕННЯМ ПЛАЗМОЮ КСПП Х-50
В УМОВАХ, ХАРАКТЕРНИХ ДЛЯ ITEР
С.С. Геращенко, В.О. Махлай, М.М. Аксьонов, Б. Базилев, О.В. Бирка, В.В. Чеботарев,
М.В. Кулик, С.І. Лебедєв, П.Б. Шевчук, В.В. Стальцов
На квазістаціонарному плазмовому прискорювачі КСПП Х-50 проведено експериментальне вивчення ерозії
зубчастих мішеней під впливом поверхневих теплових (питома енергія і тривалість імпульсу) і
корпускулярних навантажень, характерних для режимів ELM в ІТЕР. Пошкодження поверхні, механізми
ежекції частинок в твердій і крапельній фазі з різних частин мішені досліджені в залежності від кількості
плазмових імпульсів. Показано, що динаміка руху розплаву на межах структур, розбризкування крапель і
поява «містків» розплаву через зазори між складовими мішені є визначальними процесами в макроскопічній
ерозії складених поверхневих структур.
http://www.scopus.com/source/sourceInfo.url?sourceId=29021&origin=recordpage
|