Characterization of QSPA plasma streams in plasma-surface interaction experiments: simulation of ITER disduption
Experimental simulations of thermal stage of ITER disruptions with relevant surface heat loads (energy density up to 30 MJ/m² ) were performed with a quasi-steady-state plasma accelerator QSPA Kh-50. It was found, that the melt motion driven by plasma pressure gradient dominates in tungsten macrosco...
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irk-123456789-1091482016-11-21T03:03:05Z Characterization of QSPA plasma streams in plasma-surface interaction experiments: simulation of ITER disduption Makhlaj, V.A. Динамика плазмы и взаимодействие плазмы со стенкой Experimental simulations of thermal stage of ITER disruptions with relevant surface heat loads (energy density up to 30 MJ/m² ) were performed with a quasi-steady-state plasma accelerator QSPA Kh-50. It was found, that the melt motion driven by plasma pressure gradient dominates in tungsten macroscopic erosion, resulting in droplet splashing and formation of the craters with rather large edge ridges of displaced material. The contribution of mass loss to surface erosion is negligible in comparison with surface profile development caused by melt motion. Экспериментальное моделирование тепловой фазы срыва тока в ИТЭР с соответствующими тепловыми нагрузками на поверхности (плотность энергии до 30 МДж/м²) было выполнено в квазистационарном плазменном ускорителе КСПУ Х-50. Было установлено, что движение расплава, обусловленное градиентом давления плазмы, доминирует в макроскопической эрозии вольфрама и приводит к разбрызгиванию капель и образованию кратеров с большими горами перемещенного материала на их границах. Вклад массовых потерь в эрозию поверхности пренебрежимо мала по сравнению с развитием профиля поверхности, обусловленным движением расплава. Експериментальне моделювання теплової фази зрива струму в ІТЕР з відповідними тепловими навантаженнями на поверхні (густина енергії до 30 МДж/м²) було виконано в квазістаціонарному плазмовому прискорювачі КСПП Х-50. Було встановлено, що рух розплаву, обумовлений градієнтом тиску плазми, домінує в макроскопічній ерозії вольфраму приводить до розбризкування крапель і утворення кратерів з досить великими граничними горами переміщеного матеріалу. Внесок масових втрат в ерозію поверхні э незначним в порівнянні з розвитком профілю поверхні, що обумовлений рухом розплаву. 2012 Article Characterization of QSPA plasma streams in plasma-surface interaction experiments: simulation of ITER disduption / V.A. Makhlaj // Вопросы атомной науки и техники. — 2012. — № 6. — С. 126-128. — Бібліогр.: 13 назв. — англ. 1562-6016 PACS:52.40.Hf http://dspace.nbuv.gov.ua/handle/123456789/109148 en Вопросы атомной науки и техники Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
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Динамика плазмы и взаимодействие плазмы со стенкой Динамика плазмы и взаимодействие плазмы со стенкой |
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Динамика плазмы и взаимодействие плазмы со стенкой Динамика плазмы и взаимодействие плазмы со стенкой Makhlaj, V.A. Characterization of QSPA plasma streams in plasma-surface interaction experiments: simulation of ITER disduption Вопросы атомной науки и техники |
| description |
Experimental simulations of thermal stage of ITER disruptions with relevant surface heat loads (energy density up to 30 MJ/m² ) were performed with a quasi-steady-state plasma accelerator QSPA Kh-50. It was found, that the melt motion driven by plasma pressure gradient dominates in tungsten macroscopic erosion, resulting in droplet splashing and formation of the craters with rather large edge ridges of displaced material. The contribution of mass loss to surface erosion is negligible in comparison with surface profile development caused by melt motion. |
| format |
Article |
| author |
Makhlaj, V.A. |
| author_facet |
Makhlaj, V.A. |
| author_sort |
Makhlaj, V.A. |
| title |
Characterization of QSPA plasma streams in plasma-surface interaction experiments: simulation of ITER disduption |
| title_short |
Characterization of QSPA plasma streams in plasma-surface interaction experiments: simulation of ITER disduption |
| title_full |
Characterization of QSPA plasma streams in plasma-surface interaction experiments: simulation of ITER disduption |
| title_fullStr |
Characterization of QSPA plasma streams in plasma-surface interaction experiments: simulation of ITER disduption |
| title_full_unstemmed |
Characterization of QSPA plasma streams in plasma-surface interaction experiments: simulation of ITER disduption |
| title_sort |
characterization of qspa plasma streams in plasma-surface interaction experiments: simulation of iter disduption |
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
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2012 |
| topic_facet |
Динамика плазмы и взаимодействие плазмы со стенкой |
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http://dspace.nbuv.gov.ua/handle/123456789/109148 |
| citation_txt |
Characterization of QSPA plasma streams in plasma-surface interaction experiments: simulation of ITER disduption / V.A. Makhlaj // Вопросы атомной науки и техники. — 2012. — № 6. — С. 126-128. — Бібліогр.: 13 назв. — англ. |
| series |
Вопросы атомной науки и техники |
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AT makhlajva characterizationofqspaplasmastreamsinplasmasurfaceinteractionexperimentssimulationofiterdisduption |
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2025-07-07T22:37:58Z |
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2025-07-07T22:37:58Z |
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1837029527542300672 |
| fulltext |
126 ISSN 1562-6016. ВАНТ. 2012. №6(82)
CHARACTERIZATION OF QSPA PLASMA STREAMS IN PLASMA -SURFACE
INTERACTION EXPERIMENTS: SIMULATION OF ITER DISRUPTION
V.A. Makhlaj
Institute of Plasma Physics NSC “Kharkov Institute of Physics and Technology”, Kharkov, Ukraine
E-mail: makhlay@ipp.kharkov.ua
Experimental simulations of thermal stage of ITER disruptions with relevant surface heat loads (energy density
up to 30 MJ/m
2
) were performed with a quasi-steady-state plasma accelerator QSPA Kh-50. It was found, that the
melt motion driven by plasma pressure gradient dominates in tungsten macroscopic erosion, resulting in droplet
splashing and formation of the craters with rather large edge ridges of displaced material. The contribution of mass
loss to surface erosion is negligible in comparison with surface profile development caused by melt motion.
PACS:52.40.Hf
INTRODUCTION
The lifetime of the divertor and first wall armor
against high heat loads during off-normal events
(disruption and Vertical Displacement Event (VDE)) is
of concern in the design of a tokamak fusion reactors
like ITER and DEMO. The materials at the ITER-
divertor surfaces will be exposed to a steady-state heat
load with a power density of 5…10 MW/m
2
as well as
transient heat loads applied during plasma disruptions
(several 10 MJ/m
2
for several ms), VDE (up to 200
MJ/m
2
for 0.5...5 ms) and large edge localize modes
(ELMs, in the order of 1 MJ/m
2
for 0.5 ms) [1, 2].
For the transition events, the heat loads to ITER
divertor components are far above of that in available
tokamaks. Therefore, at present the results obtained
with powerful plasma accelerators [3, 4] and e-beam
facilities [5, 6] are used for experimental simulation of
targets erosion under high heat loads and for validation
of predictive models [7-10]. Experimental and
theoretical investigations [3, 4, 7-9] have shown that
disruption heat loads result in a sudden evaporation of a
thin surface layer and produce a cloud of dense vapor
plasma, which acts as a thermal shield. Dense vapor
plasma stops the incident plasma stream and transforms
the incoming energy flux into photon radiation thereby
reducing a surface heat load. Due to the vapor shielding
effect, material vaporization decreases considerably.
This paper presents the characteristics of QSPA Kh -
50 plasma streams and analysis of contribution of
different erosion mechanisms to the material damage
under plasma heat loads expected for ITER disruptions.
1. EXPERIMENTAL FACILITY AND
DIAGNOSTICS
Experiments were carried out in QSPA Kh-50
device (Fig.1) the largest and most powerful device of
this kind [3, 10]. Plasma streams, generated by QSPA
Kh-50 were injected into magnetic system of 1.6 m in
length and 0.44 m in inner diameter consisting of 4
separate magnetic coils. The maximum value of
magnetic field B0=0.54 T was achieved in diagnostic
chamber ZS = 2.3 m from accelerator output (in the
region between 3 and 4 magnetic coils) [10, 11].
Values of plasma stream energy density were
determined on the basis of time resolved measurements
of the plasma stream density and its velocity. Pressure of
plasma stream was measured of piezodetectors [12]. The
energy density in the shielding layer was measured by
displacing the calorimeter through a hole in the center of
the sample. The calorimeter could be moved into the
near-surface plasma up to the distance of 5 cm from the
target. A surface analysis was carried out with an MMR-4
optical microscope equipped with a CCD camera. Targets
were exposed to perpendicular and inclined plasma
irradiation with various numbers of pulses. The scheme
of the experiment is presented in Fig.1.
2. EXPERIMENTAL RESULTS
2.1. PARAMETERS OF IMPACTED PLASMA
STREAMS
QSPA plasma stream parameters were varied by both
changing the dynamics and quantity of gas filled the
Fig. 1. Scheme of experiment
mailto:makhlay@ipp.kharkov.ua
ISSN 1562-6016. ВАНТ. 2012. №6(82) 127
accelerator channel and changing the working voltage
of capacitor battery of the main discharge. To achieve
the working regimes for simulation the disruption-like
plasma impacts, the main attention in these experiments
was paid to possibility of effective variation of plasma
stream energy density in wide range and determination
of target heat load in dependence on plasma stream
energy density.
Special efforts were done to increase the plasma
pressure in QSPA plasma stream. As it follows from
temporal dependence of plasma stream pressure
measured at the target position (Fig. 2), maximum value
of plasma pressure achieved 1.6…1.8 MPa. Energy
density is up to 30 MJ/m
2
.
Injection of powerful plasma streams into magnetic
field is accompanied by magnetic field displacement out
of plasma. The magnetic field displaced by plasma is of
order ∆B/B0 ∼ 0.7. The temporal behavior of the signal
of displaced magnetic field is not differs from the
temporal dependence of the plasma pressure (Fig. 2).
Average β = 8πP/B0
2
value, calculated on the basis of
plasma pressure and vacuum magnetic field is about
0.4…0.6.
0 50 100 150 200 250 300
0,0
0,5
1,0
1,5
2,0
t, s
р
,
М
P
а
0,00
0,24
0,48
0,72
0,96
p
B
B/B
0
Fig. 2. Time dependencies of plasma pressure (P) and
displaced magnetic field (∆B), normalized by the value
of vacuum magnetic field (B0=0.54 T), in diagnostic
vacuum chamber
2.2. FEATURES OF PLASMA–SURFACE
INTERACTION
Protective screens of 12 cm in diameter with central
holes of 1 and 3 cm in diameter were used to impose a
pressure gradient along the target that mimics the
pressure gradient found at the strike point locations in a
tokamak disruption [7]. Measurements of plasma
pressure distribution along the target in the presence of
diaphragm are performed with a piezodetector inserted
instead of the target. It shows a steep decrease of pressure
value at the 5 mm peripheral zone and a practical
constant pressure value in central region of about 2 cm in
diameter (Fig. 3). Availability of diaphragm allowed to
make clear the influence of plasma pressure gradient on
melt motion even for QSPA plasma pulse duration and to
achieve the melt velocities comparable with ones
expected for ITER disruptions [11].
Measurements of target heat load have been
performed with small calorimeter inserted into the target
surface. In this case, the fraction of plasma energy
density delivered to the target surface is monitored (Fig.
3). As it was shown earlier [4] the main feature of high-
power plasma interaction with targets is possibility of
dense plasma shield formation close to the target
surface.
For inclined exposure of the different targets, the
diminution of energy density delivered to surface is
observed with decrease of incidence angle and diameter
of diaphragms' central hole (Fig. 4).
-3 -2 -1 0 1 2 3
0,0
0,5
1,0
1,5
2,0
31
P q
q, MJ/m
2
3 cm Hole projection
P, MPa
R, cm
0,00
0,25
0,50
0,75
1,00
2
Fig. 3. Radial distributions of plasma stream pressure
(1), energy density (2) delivered to surface target
through the diaphragm with central hole of 3 cm and
pressure of free plasma stream (3)
0 30 60 90
0.0
0.8
0.6
0.4
, degrees
D=12 cm
D=3 cm
D=1 cm
q
,
M
J
/m
2
0.2
Fig. 4. Heat load to the target surface thought
diaphragm of deferent diameter (D) versus the
incidence angle of an impinging plasma stream at an
energy density of 30 MJ/m
2
2.3. MECHANISMS OF TUNGSTEN EROSION
As it is found from profilometry, the ridges of
resolidified material, indicating the melt motion,
appeared at the melt edge (Fig. 5). For perpendicular
impacts, the height of the ridge achieves 48 m after
20 pulses (see Fig. 5,a). The distance between ridge peaks
achieves 1.4 cm. The high value of the surface roughness
masks the erosion crater between the ridge peaks. The
melt motion is accompanied by splashing of the metal
droplets of the sizes up to 100 m onto unexposed target
surface [13]. The plasma pressure gradient is the main
force initiating the melt motion [11].
For inclined exposure of the tungsten target under
the angle of 30º to the surface, the formation of a mound
of resolidified material is observed only at the
downstream part of the melt spot (see Fig. 5,b). The
mound height is 26 m, which is almost twice less than
that found for perpendicular plasma impact. Mass loss
128 ISSN 1562-6016. ВАНТ. 2012. №6(82)
measurements indicated that the contribution of
evaporation to the target erosion remains below
0.1 m/pulse.
a
b
Fig. 5. Melt layer erosion profiles for tungsten targets
under perpendicular (a) and inclined (b) impact of
plasma stream. Hole diameter is 1cm
For surface cracking the balance of the 2 processes is
observed for increased number of exposures: the cracks
become completely covered by the molten material but
new thin cracks meanwhile appear.
CONCLUSIONS
Operation regime of QSPA Kh-50 with plasma
energy density of about 25…30 MJ/m
2
was used for
experimental simulation of disruptive heat loads. The
value of energy density absorbed by the target surface is
not exceeded 0.7 MJ/m
2
for incident plasma energy
density up to 30 MJ/m
2
. This is an influence of a vapor
shield formation close to the surface under the plasma
impact.
The melt motion driven by plasma pressure gradient
dominates in tungsten macroscopic erosion, resulting in
droplet splashing and formation of the craters with
rather large edge ridges of displaced material.
This work is supported in part by STCU project # P405.
The author would like to acknowledge I.E. Garkusha for
very helpful discussion and interpretation of
experimental results and QSPA Kh-50-team for
assisting in the experiments.
REFERENCES
1. G. Federici et al. // Nucl. Fus. 2001, v. 41, p. 1967.
2. A. Loarte et. al. // Plasma Phys. Control. Fusion
2003, v. 45, p. 1549.
3. N. Arkhipov. et al. // J. Nucl. Mater. 1996, v. 233–
237, p. 686
4 V.V. Chebotarev et al. // J. Nucl. Mater. 1996, v. 233-
237, p.736-740.
5. P. Majerus et al. // Fus. Eng. and Design. 2005,
v. 75–79, p. 365–369.
6. V.T. Astrelin et al. // Nucl. Fus. 1997, v. 37, p. 1541.
7. H. Wuerz et al. // J. Nucl. Mater. 2002. v. 307-311,p. 60.
8. H. Wuerz et al. // J. Nucl. Mater. 2001, v. 290-293,
p. 1138-1143.
9. A. Hassanein, I. Konkashbaev // J. Nucl. Mater.
1996, v. 233–237, p.713–717.
10. V.I. Tereshin et al. // Brazilian Journal of Physics.
2002, v. 32, №1, p. 165-171.
11. V.I. Tereshin et al. // J. Nucl. Mater. 2003, v. 313–
316, p. 685–689.
12. A.N. Bandura et al. // Phys. Scr. 2006, v. T123,
p. 84-88.
13. I.E. Garkusha et al. // J. Nucl. Mater. 2005, v. 337–
339, p. 707–711.
Article received 14.11.2012
ХАРАКТЕРИСТИКА КСПУ ПОТОКОВ ПЛАЗМЫ В ЭКСПЕРИМЕНТАХ ПО ПЛАЗМО-
ПОВЕРХНОСТОМУ ВЗАИМОДЕЙСТВИЮ: МОДЕЛИРОВАНИЕ СРЫВОВ ТОКА В ИТЕР
В.А. Махлай
Экспериментальное моделирование тепловой фазы срыва тока в ИТЭР с соответствующими тепловыми
нагрузками на поверхности (плотность энергии до 30 МДж/м
2
) было выполнено в квазистационарном
плазменном ускорителе КСПУ Х-50. Было установлено, что движение расплава, обусловленное градиентом
давления плазмы, доминирует в макроскопической эрозии вольфрама и приводит к разбрызгиванию капель
и образованию кратеров с большими горами перемещенного материала на их границах. Вклад массовых
потерь в эрозию поверхности пренебрежимо мала по сравнению с развитием профиля поверхности,
обусловленным движением расплава.
ХАРАКТЕРИСТИКА КСПП ПОТОКІВ ПЛАЗМИ В ЕКСПЕРИМЕНТАХ ПО ПЛАЗМО-
ПОВЕРХНЕВІЙ ВЗАЄМОДІЇ: МОДЕЛЮВАННЯ ЗРИВІВ СТРУМУ В ІТЕР
В.О. Махлай
Експериментальне моделювання теплової фази зрива струму в ІТЕР з відповідними тепловими
навантаженнями на поверхні (густина енергії до 30 МДж/м
2
) було виконано в квазістаціонарному
плазмовому прискорювачі КСПП Х-50. Було встановлено, що рух розплаву, обумовлений градієнтом тиску
плазми, домінує в макроскопічній ерозії вольфраму приводить до розбризкування крапель і утворення
кратерів з досить великими граничними горами переміщеного матеріалу. Внесок масових втрат в ерозію
поверхні э незначним в порівнянні з розвитком профілю поверхні, що обумовлений рухом розплаву.
http://www.iop.org/EJ/search_author?query2=A%20N%20Bandura&searchfield2=authors&journaltype=all&datetype=all&sort=date_cover&submit=1
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