Testing of CFC targets by plasma heat fluxes relevant to ELMs and mitigated disruptions in ITER
Carbon fibre composite (CFC) was irradiated by hot plasma streams at plasma gun facility MK-200UG. The CFC targets were tested by plasma loads relevant to Edge Localised Modes (ELM) and mitigated disruptions in ITER. Onset condition of CFC evaporation and properties of evaporated carbon were studi...
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nasplib_isofts_kiev_ua-123456789-817852025-02-23T18:59:53Z Testing of CFC targets by plasma heat fluxes relevant to ELMs and mitigated disruptions in ITER Safronov, V.M. Arkhipov, N.I. Landman, I. Strunnikov, V.M. Toporkov, D.A. Zhitlukhin, A.M. ITER and fusion reactor aspects Carbon fibre composite (CFC) was irradiated by hot plasma streams at plasma gun facility MK-200UG. The CFC targets were tested by plasma loads relevant to Edge Localised Modes (ELM) and mitigated disruptions in ITER. Onset condition of CFC evaporation and properties of evaporated carbon were studied by use of infrared pyrometry and visible spectroscopy. 2006 Article Testing of CFC targets by plasma heat fluxes relevant to ELMs and mitigated disruptions in ITER / V.M. Safronov, N.I. Arkhipov, I. Landman, V.M. Strunnikov, D.A. Toporkov, A.M. Zhitlukhin // Вопросы атомной науки и техники. — 2006. — № 6. — С. 71-73. — Бібліогр.: 9 назв. — англ. 1562-6016 PACS: 52.75.–d, 52.70.–m, 52.40.Hf, 28.52 https://nasplib.isofts.kiev.ua/handle/123456789/81785 en Вопросы атомной науки и техники application/pdf Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
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ITER and fusion reactor aspects ITER and fusion reactor aspects |
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ITER and fusion reactor aspects ITER and fusion reactor aspects Safronov, V.M. Arkhipov, N.I. Landman, I. Strunnikov, V.M. Toporkov, D.A. Zhitlukhin, A.M. Testing of CFC targets by plasma heat fluxes relevant to ELMs and mitigated disruptions in ITER Вопросы атомной науки и техники |
| description |
Carbon fibre composite (CFC) was irradiated by hot plasma streams at plasma gun facility MK-200UG. The CFC
targets were tested by plasma loads relevant to Edge Localised Modes (ELM) and mitigated disruptions in ITER. Onset
condition of CFC evaporation and properties of evaporated carbon were studied by use of infrared pyrometry and
visible spectroscopy. |
| format |
Article |
| author |
Safronov, V.M. Arkhipov, N.I. Landman, I. Strunnikov, V.M. Toporkov, D.A. Zhitlukhin, A.M. |
| author_facet |
Safronov, V.M. Arkhipov, N.I. Landman, I. Strunnikov, V.M. Toporkov, D.A. Zhitlukhin, A.M. |
| author_sort |
Safronov, V.M. |
| title |
Testing of CFC targets by plasma heat fluxes relevant to ELMs and mitigated disruptions in ITER |
| title_short |
Testing of CFC targets by plasma heat fluxes relevant to ELMs and mitigated disruptions in ITER |
| title_full |
Testing of CFC targets by plasma heat fluxes relevant to ELMs and mitigated disruptions in ITER |
| title_fullStr |
Testing of CFC targets by plasma heat fluxes relevant to ELMs and mitigated disruptions in ITER |
| title_full_unstemmed |
Testing of CFC targets by plasma heat fluxes relevant to ELMs and mitigated disruptions in ITER |
| title_sort |
testing of cfc targets by plasma heat fluxes relevant to elms and mitigated disruptions in iter |
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| publishDate |
2006 |
| topic_facet |
ITER and fusion reactor aspects |
| url |
https://nasplib.isofts.kiev.ua/handle/123456789/81785 |
| citation_txt |
Testing of CFC targets by plasma heat fluxes relevant to ELMs and mitigated disruptions in ITER / V.M. Safronov, N.I. Arkhipov, I. Landman, V.M. Strunnikov, D.A. Toporkov, A.M. Zhitlukhin // Вопросы атомной науки и техники. — 2006. — № 6. — С. 71-73. — Бібліогр.: 9 назв. — англ. |
| series |
Вопросы атомной науки и техники |
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2025-11-24T14:18:47Z |
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2025-11-24T14:18:47Z |
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| fulltext |
ITER AND FUSION REACTOR ASPECTS
Problems of Atomic Science and Technology. 2006, 6. Series: Plasma Physics (12), p. 71-73 71
TESTING OF CFC TARGETS BY PLASMA HEAT FLUXES RELEVANT
TO ELMS AND MITIGATED DISRUPTIONS IN ITER
V.M. Safronov1, N.I. Arkhipov1, I. Landman2, V.M. Strunnikov1,
D.A. Toporkov1, A.M. Zhitlukhin1
1 State Research Center of Russian Federation Troitsk Institute
for Innovation and Fusion Research, 142190 Troitsk, Moscow reg., Russia
2Forschungszentrum Karlsruhe, IHM, Postfach 3640, 76021 Karlsruhe, Germany
Carbon fibre composite (CFC) was irradiated by hot plasma streams at plasma gun facility MK-200UG. The CFC
targets were tested by plasma loads relevant to Edge Localised Modes (ELM) and mitigated disruptions in ITER. Onset
condition of CFC evaporation and properties of evaporated carbon were studied by use of infrared pyrometry and
visible spectroscopy.
PACS: 52.75.–d, 52.70.–m, 52.40.Hf, 28.52
1. INTRODUCTION
Some key issues remain in the ITER design associated
with the response of the armour materials to thermal
energy deposited during Edge Localised Modes (ELMs)
and mitigated disruptions. They include the erosion
effects in the armour materials, the resultant production
and transport of impurities in tokamak plasma during and
after the ELM, and the potential for plasma contamination
during the inter-ELM phase. These effects are not fully
understood and require further experimental and
theoretical studies.
The heat loads on the ITER divertor target are
expected [1] to be:
- 0.5…4 MJ/m2 in time scale of 0.1…0.5 ms for Type I
ELM;
- 2…13 MJ/m2 in time scale of 1…3 ms for thermal
quench phase of disruption.
The expected heat loads are not achievable in the existing
tokamak-machines. Therefore the divertor armour
materials are tested by use of other devices such as
powerful plasma guns [2-4] and e-beam facilities [5,6],
which are capable to simulate, at least in part, the loading
conditions of interest. Experimental results are used for
validation of the numerical models developed for
simulation of the armour behavior during ELMs and
disruptions [7-9].
Carbon fibre composite (CFC) and tungsten are
foreseen as candidate armour materials for ITER divertor.
The present work refers to experimental investigation of
CFC armour. The CFC targets were tested at plasma gun
facility MK-200UG by plasma heat loads relevant to the
ITER Type I ELMs and mitigated disruptions. A
threshold of CFC evaporation has been measured and
properties of the evaporated carbon have been studied as a
function of the plasma heat load. First testing of CFC cut
has been performed also.
2. EXPERIMENTAL
The basic scheme of the MK-200UG facility is shown
in Fig.1. The facility consists of a pulsed plasma gun, a
long drift tube and a target chamber.
The plasma gun is fed from 1152 µF capacitor bank.
In the present experiment the operating voltage was
13 kV. It corresponds to about 100kJ of energy stored in
the capacitor bank.
plasma 9.5-m drift tube target
gun transportation compression chamber
zone zone
1 2
gas puff electrodes magnetic coils viewing ports target
Fig.1. Basic scheme of MK-200UG facility
The plasma gun injects a hydrogen plasma stream into
the drift tube, consisting of 6.5 m cylindrical part and of a
conical one with a length of 3 m. Diameter of the
cylindrical tube is 30 cm. At the conical section, the tube
diameter reduces towards its exit from 30 cm to 15 cm.
The cylindrical tube is filled with a 0.7 T longitudinal
magnetic field. The magnetic field rises from 0.7 T up to
2.5 T along the conical part. In the magnetic cone, a quick
magnetization of the plasma stream occurs and after that
the plasma moves strictly along the magnetic field lines.
The CFC targets are placed in the target chamber
equipped by the diagnostic tools. The targets are tested at
a varying plasma load. The plasma load is varied by
means of variation of the magnetic field in the target
chamber: the larger magnetic field, the larger plasma heat
load. The plasma load grows with the magnetic field
because of increasing plasma density; plasma stream
velocity and impact ion energy remain unaltered.
Parameters of hydrogen plasma stream at the target
position are listed in Table1.
Table 1. Plasma stream parameters
energy density q = 0.6…1.5 MJ/m2
power density w = 10…30 GW/m2
pulse duration τ = 0.05…0.06 ms
impact ion energy Ei = 2…3 keV
plasma density n = (0.5…2)×1020 m-3
plasma pressure P < 1 bar
diameter D = 6…10 cm
The table shows the energy density measured at the
axis of the plasma stream. A real plasma load on the
target surface qs(r) depends on a radial position r of the
target and on an angle α of the target inclination in
72
respect to the stream axis qs(r) = q(r) sin α. In the present
experiment, the CFC targets were tested by plasma load
varying in the range 0.1…1 MJ/m2.
The CFC targets have a rectangular shape with a face
surface 25 x 25mm and 45 x 25mm and thickness 10mm.
The targets are equipped by thermocouples for the
measurement of absorbed energy.
A temperature of the target surface was measured by
use of infrared pyrometer over a whole period of
plasma/surface interaction. Visible and EUV spectroscopy
was applied for analysis of the evaporated carbon.
3. EXPERIMENTAL RESULTS
Onset condition of CFC evaporation was studied by
the following method: CFC target was exposed to
increasing plasma load; a temperature of the exposed
target surface was measured by infrared pyrometer; an
appearance of carbon vapor was detected by means of
spectroscopy. The performed investigation has shown:
- measurable but a very weak evaporation starts at
plasma load q = 0.15 MJ/m2;
- intense evaporation of CFC occurs at plasma heat
load q > 0.2 MJ/m2;
- evaporation is surely absent at q < 0.1 MJ/m2.
A temperature of the target surface increases with the
plasma heat load q and it runs up to a maximum
magnitude T = 3700…3800 K (Fig.2) at q = 0.2 MJ/m2,
when the intense evaporation starts. At further increase of
the plasma load up to q = 1 MJ/m2, the temperature
remains unaltered. (It should be noted that the pyrometer
was adjusted for temperatures above 2000 K, therefore a
tail part of the plot in Fig.2 is not correct.)
0
500
1000
1500
2000
2500
3000
3500
4000
-50 0 50 100 150 200t,mks
T, oK
CFC
Fig.2. Surface temperature of CFC target exposed to
plasma stream at heat load 0.24 MJ/m2
By means of visible spectroscopy and photography it
was measured that the evaporated carbon moves from the
target surface along the magnetic field lines. Transverse
motion is negligible. A first front of the carbon cloud
moves with a velocity V = (1…2) ×104 cm/s.
Spectrum of the evaporated carbon consists of
separate spectral lines, continuous spectrum is observed
near the target surface only, at distances 1…2 mm. At
heat load q < 0.2 MJ/m2, carbon vapor emits mainly in the
visible spectral range. EUV spectral lines CV (40.3Å) and
CVI (33.7 Å) (Fig.3) appear at heat load q = 0.2 MJ/m2
and q = 0.3 MJ/m2 correspondingly. Analysis of the
obtained spectral data gives a temperature of the
evaporated carbon about T = 10 eV for plasma load of
q = 0.2 MJ/m2 and T = 30 eV for q = 0.3 MJ/m2.
50
100
150
200
250
0 50 100 150 200 250
F_01_5-10mm
CFC plasma spectrum
in
te
ns
ity
, r
.u
.
Wavelenght, Å
C
V
18
6.
7A
1
s2
p-
1s
4d
CV
I
33
.7
A
1
s-
2p
C
V
4
0.
3A
1
s2 -1
s2
p
C
V
17
3.
3A
1
s2
s-
1s
4p
C
V
16
7.
4A
1
s2
p-
1s
5d
C
V
2p
-6
d,
2
p-
7d
, 2
p-
8d
Fig.3.EUV spectrum of carbon plasma at q = 0.32 MJ/m2
Electron density ne of carbon plasma was evaluated
from Stark broadening of spectral line CIV (4658.3 Å).
Table 2 illustrates a magnitude of ne as a function of the
plasma load. Density was measured at times t= 10…15 µs
after a start of plasma/target interaction at a distance
0.5 cm from the target surface.
Table 2. Electron density of carbon plasma
Plasma load, MJ/m2 Electron density, cm-3
0.15 Not measurable, ne << 1016
0.17 1.4 ×1016
0.20 1.6 ×1017
0.25 1.8 ×1017
0.30 2.0 ×1017
0.37 2.1 ×1017
According to the obtained data, a density of the
evaporated carbon grows with increase of the plasma
load. At first, the density grows quickly: small variation
of the plasma load from q = 0.17 MJ/m2 to - 0.20 MJ/m2
results in increase of the density by a factor of 10. At
larger plasma loads q > 0.20 MJ/m2 the density rises
slightly and it remains practically constant value
ne = 2×1017 cm-3. These findings indicate that a threshold
of intense CFC evaporation is about q = 0.2 MJ/m2.
0
5
10
15
20
25
0 5 10 15
G_14_42_79_frames
Q = 0.30 MJ/m2
n
e
, 1016 cm-3
E
le
ct
ro
n
de
ns
ity
n
e, 1
016
c
m
-3
Distance X, cm
Fig.4. Space distribution of electron density in front of
CFC target (plasma heat load 0.3 MJ/m2, time 13 µs)
73
Fig.4 shows a space distribution of electron density in
front of the target. The density is maximal near the
surface and it reduces steeply with a distance. Carbon
target plasma consists of a dense near-surface plasma
(ne=2×1017cm-3) and carbon plasma corona
(ne=(1…2)×1016cm-3), which expands from the target
surface with a velocity V = (1…2)×104 cm/s. Taking into
account that the plasma corona consists mainly of C+3
ions we can conclude that a density of carbon ions is
n > 1015 cm-3 that is larger than a density of tokamak
plasma. It means that during ELMs, large amount of
carbon impurities might move from the divertor to main
chamber and it might cause a radiative cooling of
tokamak plasma.
CFC consists of PAN carbon fibres, which are parallel
to the face target surface, and perpendicular pitch fibres.
PAN fibres have smaller thermal conductivity than the
pitch fibres and therefore the PAN fibres should evaporate
at smaller heat loads and more intensively than the pitch
fibres. This assumption has been verified.
Fig.5. Image of plasma irradiated CFC surface
Fig.5 presents image of the exposed CFC surface. It is
clearly seen a modulation of radiation over the exposed
target surface: there are dark PAN fibres and light pitch
fibres. PAN fibres evaporate stronger than the pitch fibres
therefore they look darker. There was tested also CFC cut,
in which PAN and pitch fibres are oriented at 45 degree to
the face surface. It was found that a radiation is fully
homogeneous over a whole surface of the exposed cut.
CONCLUSIONS
CFC targets were tested by hot magnetized plasma
streams at heat loads q = 0.1…1 MJ/m2 and pulse
duration 0.05 ms. The obtained results are the following:
- Intense evaporation of CFC starts at q = 0.2 MJ/m2
and surface temperature Ts =3700…3800 K.
- At q = 0.2…03 MJ/m2, electron density of carbon
plasma is of ne = 2×1017 cm-3 at 0.5 cm distance.
- Carbon plasma corona (ne = (1…2)×1016 cm-3) moves
from the target surface along the magnetic field lines
with a velocity (1…2)×104 cm/s.
- Carbon plasma consists of C+2 – C+5 ions.
Temperature of evaporated carbon is T = 10-30 eV at
q = 0.2-03 MJ/m2.
- In standard CFC target, PAN fibres evaporate more
intensively than pitch fibres. In CFC cut, all fibres
evaporate with equal rate.
REFERENCES
1. ITER Physics Basis//Nucl. Fusion. 1999, v.39,
p.2137.
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.
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