Experimental study of tungsten impurity formation and dynamics at plasma gun facility MK-200 under condition relevant to transient events in ITER
Tungsten targets were irradiated by intense plasma streams at plasma gun facility MK-200UG. The targets were tested by plasma loads relevant to Edge Localised Modes (ELM) and mitigated disruptions in ITER. Primary attention has been focused on investigation of impurity formation due to tungsten evap...
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| Cite this: | Experimental study of tungsten impurity formation and dynamics at plasma gun facility MK-200 under condition relevant to transient events in ITER / I.M. Poznyak, N.I. Arkhipov, S.V. Karelov, V.M. Safronov , D.A. Toporkov // Вопросы атомной науки и техники. — 2012. — № 6. — С. 52-54. — Бібліогр.: 10 назв. — англ. |
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nasplib_isofts_kiev_ua-123456789-1091002025-02-09T21:12:36Z Experimental study of tungsten impurity formation and dynamics at plasma gun facility MK-200 under condition relevant to transient events in ITER Экспериментальные исследования формирования и динамики примесей вольфрама на плазменной установке MK-200UG в условиях, характерных для переходных процессов в ITER Експериментальні дослідження формування і динаміки домішок вольфраму на плазмовій установці MK-200UG в умовах, характерних для перехідних процесів в ITER Poznyak, I.M. Arkhipov, N.I. Karelov, S.V. Safronov, V.M. Toporkov, D.A. ИТЭР и приложения для термоядерного реактора Tungsten targets were irradiated by intense plasma streams at plasma gun facility MK-200UG. The targets were tested by plasma loads relevant to Edge Localised Modes (ELM) and mitigated disruptions in ITER. Primary attention has been focused on investigation of impurity formation due to tungsten evaporation and on investigation of impurity transport along the magnetic field lines. Мишени из вольфрама были подвергнуты воздействию интенсивных потоков плазмы на плазменном ускорителе МК-200UG. Испытания проводились при плазменных нагрузках, характерных для ELM’ов и ослабленных срывов в ITER. Исследованы процессы формирования примесей вольфрама за счет испарения материала мишени и их распространения вдоль силовых линий магнитного поля. Мішені з вольфраму були піддані впливу інтенсивних потоків плазми на плазмовому прискорювачі МК- 200UG. Випробування проводилися при плазмових навантаженнях, характерних для ELM’ів і послаблених зривів в ITER. Досліджено процеси формування домішок вольфраму за рахунок випаровування матеріалу мішені і їх поширення уздовж силових ліній магнітного поля. The work is supported partly by RFBR grant № 09- 02-13562 and grant № 08-02-13612. 2012 Article Experimental study of tungsten impurity formation and dynamics at plasma gun facility MK-200 under condition relevant to transient events in ITER / I.M. Poznyak, N.I. Arkhipov, S.V. Karelov, V.M. Safronov , D.A. Toporkov // Вопросы атомной науки и техники. — 2012. — № 6. — С. 52-54. — Бібліогр.: 10 назв. — англ. 1562-6016 PACS: 52.75.–d, 52.70.–m, 52.40.Hf, 28.52 https://nasplib.isofts.kiev.ua/handle/123456789/109100 en Вопросы атомной науки и техники application/pdf Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
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ИТЭР и приложения для термоядерного реактора ИТЭР и приложения для термоядерного реактора |
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ИТЭР и приложения для термоядерного реактора ИТЭР и приложения для термоядерного реактора Poznyak, I.M. Arkhipov, N.I. Karelov, S.V. Safronov, V.M. Toporkov, D.A. Experimental study of tungsten impurity formation and dynamics at plasma gun facility MK-200 under condition relevant to transient events in ITER Вопросы атомной науки и техники |
| description |
Tungsten targets were irradiated by intense plasma streams at plasma gun facility MK-200UG. The targets were tested by plasma loads relevant to Edge Localised Modes (ELM) and mitigated disruptions in ITER. Primary attention has been focused on investigation of impurity formation due to tungsten evaporation and on investigation of impurity transport along the magnetic field lines. |
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Article |
| author |
Poznyak, I.M. Arkhipov, N.I. Karelov, S.V. Safronov, V.M. Toporkov, D.A. |
| author_facet |
Poznyak, I.M. Arkhipov, N.I. Karelov, S.V. Safronov, V.M. Toporkov, D.A. |
| author_sort |
Poznyak, I.M. |
| title |
Experimental study of tungsten impurity formation and dynamics at plasma gun facility MK-200 under condition relevant to transient events in ITER |
| title_short |
Experimental study of tungsten impurity formation and dynamics at plasma gun facility MK-200 under condition relevant to transient events in ITER |
| title_full |
Experimental study of tungsten impurity formation and dynamics at plasma gun facility MK-200 under condition relevant to transient events in ITER |
| title_fullStr |
Experimental study of tungsten impurity formation and dynamics at plasma gun facility MK-200 under condition relevant to transient events in ITER |
| title_full_unstemmed |
Experimental study of tungsten impurity formation and dynamics at plasma gun facility MK-200 under condition relevant to transient events in ITER |
| title_sort |
experimental study of tungsten impurity formation and dynamics at plasma gun facility mk-200 under condition relevant to transient events in iter |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| publishDate |
2012 |
| topic_facet |
ИТЭР и приложения для термоядерного реактора |
| url |
https://nasplib.isofts.kiev.ua/handle/123456789/109100 |
| citation_txt |
Experimental study of tungsten impurity formation and dynamics at plasma gun facility MK-200 under condition relevant to transient events in ITER / I.M. Poznyak, N.I. Arkhipov, S.V. Karelov, V.M. Safronov , D.A. Toporkov // Вопросы атомной науки и техники. — 2012. — № 6. — С. 52-54. — Бібліогр.: 10 назв. — англ. |
| series |
Вопросы атомной науки и техники |
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ITER AND FUSION REACTOR ASPECTS
52 ISSN 1562-6016. ВАНТ. 2012. №6(82)
EXPERIMENTAL STUDY OF TUNGSTEN IMPURITY FORMATION
AND DYNAMICS AT PLASMA GUN FACILITY MK-200 UNDER
CONDITION RELEVANT TO TRANSIENT EVENTS IN ITER
I.M. Poznyak, N.I. Arkhipov, S.V. Karelov, V.M. Safronov , D.A. Toporkov
State Research Center of Russian Federation Troitsk Institute
for Innovation and Fusion Research, 142190 Troitsk, Moscow, Russia
Tungsten targets were irradiated by intense plasma streams at plasma gun facility MK-200UG. The targets were
tested by plasma loads relevant to Edge Localised Modes (ELM) and mitigated disruptions in ITER. Primary
attention has been focused on investigation of impurity formation due to tungsten evaporation and on investigation
of impurity transport along the magnetic field lines.
PACS: 52.75.–d, 52.70.–m, 52.40.Hf, 28.52
INTRODUCTION
Tungsten is foreseen presently as the main candidate
armour material for the divertor targets in ITER. During
the transient processes, such as ELMs and disruptions,
the divertor armour will be exposed to the high plasma
loads [1] which can cause a severe erosion of the
armour materials. Erosion reduces lifetime of the
divertor components and leads to production of
impurities, which can penetrate into the hot fusion
plasma causing its radiative cooling. The properties of the eroded
materials are critically important to analysis of tokamak-reactor.
The plasma heat loads expected in the ITER
transient events are not achieved in the existing tokamak
machines. Therefore, behavior of candidate armour
materials is studied by use of powerful plasma guns [2-
4] and e-beam facilities [5,6], which are capable to
simulate, at least in part, the loading condition of
interest. The present work refers to experimental study
of tungsten armour. The tungsten targets have been
tested by intense plasma streams at the pulsed plasma
gun MK-200UG. The targets were examined by plasma
heat fluxes relevant to ITER ELMs and mitigated
disruptions. Primary attention has been focused at
investigation of impurity formation due to tungsten
evaporation and on investigation of impurity transport
along the magnetic field lines.
1. EXPERIMENTAL TECHNIQUE
1.1. MK-200UG FACILITY
At MK-200UG facility, the targets are tested by
magnetized hydrogen plasma streams with heat load
Q = 0.2 …1.2 MJ/m2 and pulse duration τ = 0.05 ms.
The plasma heat load Q varies by changing the plasma
density in the range n = (0.1 …2) ×1020 m-3 while the
impact ion energy remains practically unaltered Ei =
2…3 keV. Plasma pressure varies in the range P =
0.03…0.5 bar. Diameter of the plasma stream – d =
0.06…0.1 m. Plasma/target interaction occurs in the
magnetic field B = 0.5…2 T.
Plasma stream parameters such as heat flux w = Q/τ,
impact ion energy Ei, density n, pressure P, and
negligible percentage of impurities (<1%) are close to
the expected ones in ITER during the transient
processes. The disadvantage of MK-200UG facility is
small duration τ of the plasma pulse. Because of the
small pulse duration the facility is not suited for
longevity test of the divertor materials. Nevertheless it
is quite suitable to simulate the initial stage of the ITER
transient events under rather realistic plasma
parameters. These experimental data need for
development and validation of appropriate numerical
models [7-9].
1.2. DIAGNOSTICS
The targets to be tested are equipped by the
thermocouples. Energy absorbed by the target qabs is
determined from the measured target heating ΔT, known
mass m of the target and it's specific heat c: qabs = cmΔT.
EUV transmission grating based imaging
spectrograph (TGIS) is used to investigate the tungsten
plasma radiation in spectral interval Δλ = 1…40 nm. In the
present experiment, spectral dispersion is 1.8 nm/mm, spectral
resolution is 0.2 nm and spatial resolution – about 2 mm.
Fig. 1. Pinhole camera equipped AXUV photodiodes
A pinhole camera equipped AXUV-photodiodes
used to study the tungsten impurity formation and
dynamics (Fig. 1). Photodiodes are sensitive in range
Δλ = 0.02…1100 nm. A part of experiments were
carried out with a filter – a thin aluminum foil. The foil
has a transparency window Δλ = 17…80 nm.
2. EXPERIMENTAL RESULTS
2.1. EUV SPECTROSCOPY
At low plasma loads Q < 0.35 MJ/m2 tungsten
spectral lines are absent on spectrograms. Increase of
the load to Q = 0.5 MJ/m2 results in the abrupt
intensification of the EUV radiation and in the essential
change of the spectrum shape. It means that at such
plasma load the intense evaporation of tungsten begins.
Typical EUV spectra of tungsten plasma is shown
on Fig. 2. Radiation lies in the spectral range λ < 30 nm
with a maximum amplitude at λ = 16…20 nm. A
ISSN 1562-6016. ВАНТ. 2012. №6(82) 53
comparison of the measured tungsten spectra with the
calculated spectral data shows that the target plasma
contains tungsten ions ionized up to W+7 and above [10].
Fig. 2. EUV spectra of tungsten plasma
Fig. 3 shows the intensity I(x) of tungsten plasma
radiation at varying distance x from the target. The
intensity I(x) was determined by integration of EUV
radiation over the spectral interval λ = 5…30 nm.
Fig. 3. Spatial distribution of EUV radiation of tungsten
plasma
An effective thickness of the emitting layer is about
Δx ≈ 5 cm. The intensity of the tungsten radiation I(x)
reduces quickly with the distance x. Meanwhile the
impurity radiation is reliably detected at the distances
larger than x = 10 cm from the target surface.
2.2. IMPURITY DYNAMICS
The pinhole camera equipped by AXUV diodes (see
Fig. 1) enable to investigate the tungsten plasma
dynamics.
The expansion velocity V of the tungsten impurities
is evaluated by means of time-of-flight method, by
measuring the time delay between the rising edges of
the AXUV's signals (Fig. 4). In the present experiment
the velocity is about V ≈ 2·106 cm/c. It does not depend
on plasma heat load in the investigated range of the
loads.
The AXUV-diodes diagnostic is more sensitive than
TGIS-spectrograph. Therefore the diodes allow to detect
the tungsten radiation at smaller plasma loads. Thus it
was found that the energy threshold of tungsten
evaporation is Q = 0.35 MJ/m2 rather than Q =
0.5 MJ/m2 according to the EUV spectroscopy.
Fig. 5 shows the spatial distribution of the tungsten
plasma radiation. One can see that the radiation reduces
monotonically with a distance from the surface. At the
distances x ≈ 0…10 cm the impurity radiation falls
tenfold. Due to a high sensitivity the applied diagnostic
makes possible to detect the tungsten radiation up to x ≈
15…20 cm.
Fig. 4. Rising fronts of AXUV's signals at various
distances from the target surface
Fig. 5. Spatial distribution of tungsten plasma radiation,
AXUV
Fig. 6 and Fig. 7 show the spatial distribution of the
tungsten plasma radiation which is obtained by use of
the open pinhole and by the pinhole with a filter. A thin
Al foil of 0.65 μm thickness was applied as filter. Such
foil have transparency window in the wavelength range
Δλ = 17…80 nm.
Fig. 6. Spatial distribution of tungsten plasma radiation,
open pinhole
In both cases the intensity of impurity radiation
decreases monotonically and rapidly from the target
surface. At a distance of х ≈ 5 cm it falls by one order of
magnitude.
54 ISSN 1562-6016. ВАНТ. 2012. №6(82)
Fig. 7. Spatial distribution of tungsten plasma radiation,
Al foil used as filter
Comparing the obtained data one can conclud that the
basic spatial features of the radiation distribution are
defined by the radiation of the spectral range λ =
17…80 nm. The radiation of the range λ = 5…17 nm
belongs to the tungsten ions which have greater
ionization stage than the ions at λ = 17…80 nm and do
not change the typical character of the spatial
dependences.
SUMMARY
Tungsten targets were tested by intense plasma
streams at plasma gun facility MK-200UG under the
plasma heat fluxes relevant to ELMs and mitigated
disruptions in ITER.
Tungsten impurity formation and dynamics have been
studied. It’s shown that at the plasma pulse duration of
τ = 0.05 ms, EUV radiation of the tungsten plasma was
reliably detected at the plasma heat load q = 0.3 MJ/m2.
The EUV intensity of the target plasma radiation has
a maximum close to the surface and reduces with a
distance. An effective thickness of the near-surface
plasma layer, which emits in the EUV spectral band, is
about Δx = 4…5 cm. However a weak EUV radiation of
tungsten is detected up to the distance of x ≈ 20 cm.
Comparison of the measured tungsten spectra with
the calculated spectral data shows that the target plasma
contains mainly tungsten ions of ionization state W+7
and above.
It was found that the tungsten plasma velocity is
about v ≈ 2·106 cm/s for a wide range of the incoming
plasma heat loads.
The basic spatial features of the radiation
distribution are defined by the radiation in the spectral
range λ = 17…80 nm.
Based on the obtained experimental data it would be
too early to conclude that the tungsten impurities will be
localized near the divertor plates and they can’t
penetrate into the main tokamak chamber. Additional
investigation should be carried on.
ACKNOWLEDGEMENTS
The work is supported partly by RFBR grant № 09-
02-13562 and grant № 08-02-13612.
REFERENCES
1. G. Federici et al. // Plasma Phys. Control. Fusion. 2003,
v. 41, p.1523.
2. N.I. Arkhipov et al. // J. Nucl Mater. 1996, v. 233-237,
p. 686.
3. V.I. Tereshin et al. // J. Nucl. Mater. 2003, v. 313-316,
p. 767.
4. V. Belan et al.// J. Nucl. Mater. 1996, v. 233-237, p.763.
5. V.T. Astrelin et al.// Nucl. Fusion. 1997, v. 37, p.1541.
6. J.Linke et al.// J. Nucl. Mater. 1994, v. 212-215, p.1195.
7. I.S. Landman et al. // J. Nucl. Mater. 2005, v. 337-339,
p. 761.
8. S. Pestchanyi and I. Landman // Fusion Eng. Design.
2006, v. 81, p. 275.
9. B. Bazylev et al. // Physica Scripta. 2004, v. T111,
p. 213.
10. S. Pestchanyi et al. Simulation of tungsten plasma
transport along magnetic field under ELM-like heat loads //
20th International Conference PSI 2012, P2-77.
Article received 18.09.12
ЭКСПЕРИМЕНТАЛЬНЫЕ ИССЛЕДОВАНИЯ ФОРМИРОВАНИЯ И ДИНАМИКИ ПРИМЕСЕЙ
ВОЛЬФРАМА НА ПЛАЗМЕННОЙ УСТАНОВКЕ MK-200UG В УСЛОВИЯХ, ХАРАКТЕРНЫХ
ДЛЯ ПЕРЕХОДНЫХ ПРОЦЕССОВ В ITER
И.М. Позняк, Н.И. Архипов, С.В. Карелов, В.M. Сафронов, Д.А. Топорков
Мишени из вольфрама были подвергнуты воздействию интенсивных потоков плазмы на плазменном
ускорителе МК-200UG. Испытания проводились при плазменных нагрузках, характерных для ELM’ов и
ослабленных срывов в ITER. Исследованы процессы формирования примесей вольфрама за счет испарения
материала мишени и их распространения вдоль силовых линий магнитного поля.
ЕКСПЕРИМЕНТАЛЬНІ ДОСЛІДЖЕННЯ ФОРМУВАННЯ І ДИНАМІКИ ДОМІШОК ВОЛЬФРАМУ
НА ПЛАЗМОВІЙ УСТАНОВЦІ MK-200UG В УМОВАХ, ХАРАКТЕРНИХ ДЛЯ ПЕРЕХІДНИХ
ПРОЦЕСІВ В ITER
І.М. Позняк, Н.І. Архіпов, С.В. Карелов, В.M. Сафронов, Д.А. Топорков
Мішені з вольфраму були піддані впливу інтенсивних потоків плазми на плазмовому прискорювачі МК-
200UG. Випробування проводилися при плазмових навантаженнях, характерних для ELM’ів і послаблених
зривів в ITER. Досліджено процеси формування домішок вольфраму за рахунок випаровування матеріалу
мішені і їх поширення уздовж силових ліній магнітного поля.
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