Effect of exposure inside the LHD vessel on reflectance of stainless steel mirrors
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України
2002
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| Cite this: | Effect of exposure inside the LHD vessel on reflectance of stainless steel mirrors / V.S. Voitsenya, A. Sagara, A.F. Bardamid, A.I. Belyaeva, V.N. Bondarenko, A.D. Kudlenko, V.G. Konovalov, and S.I. Solodovchenko // Вопросы атомной науки и техники. — 2002. — № 5. — С. 39-41. — Бібліогр.: 4 назв. — англ. |
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Voitsenya, V.S. Sagara, A. Bardamid, A.F. Belyaeva, A.I. Bondarenko, V.N. Kudlenko, A.D. Konovalov, V.G. Solodovchenko, S.I. 2015-03-08T20:12:46Z 2015-03-08T20:12:46Z 2002 Effect of exposure inside the LHD vessel on reflectance of stainless steel mirrors / V.S. Voitsenya, A. Sagara, A.F. Bardamid, A.I. Belyaeva, V.N. Bondarenko, A.D. Kudlenko, V.G. Konovalov, and S.I. Solodovchenko // Вопросы атомной науки и техники. — 2002. — № 5. — С. 39-41. — Бібліогр.: 4 назв. — англ. 1562-6016 PACS: 52.55.Hc; 52.40.Hf https://nasplib.isofts.kiev.ua/handle/123456789/77874 en Національний науковий центр «Харківський фізико-технічний інститут» НАН України Вопросы атомной науки и техники ITER and fusion reactor aspects Effect of exposure inside the LHD vessel on reflectance of stainless steel mirrors Article published earlier |
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Effect of exposure inside the LHD vessel on reflectance of stainless steel mirrors |
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Effect of exposure inside the LHD vessel on reflectance of stainless steel mirrors Voitsenya, V.S. Sagara, A. Bardamid, A.F. Belyaeva, A.I. Bondarenko, V.N. Kudlenko, A.D. Konovalov, V.G. Solodovchenko, S.I. ITER and fusion reactor aspects |
| title_short |
Effect of exposure inside the LHD vessel on reflectance of stainless steel mirrors |
| title_full |
Effect of exposure inside the LHD vessel on reflectance of stainless steel mirrors |
| title_fullStr |
Effect of exposure inside the LHD vessel on reflectance of stainless steel mirrors |
| title_full_unstemmed |
Effect of exposure inside the LHD vessel on reflectance of stainless steel mirrors |
| title_sort |
effect of exposure inside the lhd vessel on reflectance of stainless steel mirrors |
| author |
Voitsenya, V.S. Sagara, A. Bardamid, A.F. Belyaeva, A.I. Bondarenko, V.N. Kudlenko, A.D. Konovalov, V.G. Solodovchenko, S.I. |
| author_facet |
Voitsenya, V.S. Sagara, A. Bardamid, A.F. Belyaeva, A.I. Bondarenko, V.N. Kudlenko, A.D. Konovalov, V.G. Solodovchenko, S.I. |
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ITER and fusion reactor aspects |
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ITER and fusion reactor aspects |
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2002 |
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English |
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Вопросы атомной науки и техники |
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
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Article |
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1562-6016 |
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https://nasplib.isofts.kiev.ua/handle/123456789/77874 |
| citation_txt |
Effect of exposure inside the LHD vessel on reflectance of stainless steel mirrors / V.S. Voitsenya, A. Sagara, A.F. Bardamid, A.I. Belyaeva, V.N. Bondarenko, A.D. Kudlenko, V.G. Konovalov, and S.I. Solodovchenko // Вопросы атомной науки и техники. — 2002. — № 5. — С. 39-41. — Бібліогр.: 4 назв. — англ. |
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2025-11-26T00:07:52Z |
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EFFECT OF EXPOSURE INSIDE THE LHD VESSEL ON REFLECTANCE
OF STAINLESS STEEL MIRRORS
V.S.Voitsenya, A.Sagara1, A.F.Bardamid2, A.I.Belyaeva3, V.N.Bondarenko, A.D.Kudlenko3,
V.G.Konovalov, and S.I.Solodovchenko
National Science Center KIPT, 61108 Kharkov, Ukraine;
1National Institute for Fusion Science Oroshi-cho, Toki-shi, Gifu-ken 509-5292, Japan;
2T.Shevchenko National University, Kiev, Ukraine
3Technical University, Kharkov, Ukraine
PACS: 52.55.Hc; 52.40.Hf
1. INTRODUCTION
The efficiency of in-vessel mirrors of diagnostic
systems of a fusion reactor will depend both on the mirror
material and on the mirror location inside the reactor
vacuum vessel. Till recently the data necessary to predict
the behavior under a fusion reactor environment of
mirrors fabricated of different metals with different
structure were obtained in simulation experiments only
[1]. The first attempt to study the connection between the
mirror location and modification of mirror optical
properties was made two years ago for stainless steel
mirror samples exposed inside the Large Helical Device
(LHD) [2] during one experimental campaign. In this
paper the main results obtained after investigation of
samples taken out of LHD vessel are presented.
2. EXPERIMENTAL SETUP AND INITIAL
DATA
Three mirrors of stainless steel type similar to 316 steel
with size 20x10x1 mm were mechanically polished and
cleansed in an ultrasound bath filled with acetone. The
spectral reflectance at normal incidence of samples was
measured in the wavelength range 200-700 nm, and
afterward they were installed inside the LHD vacuum
vessel as shown in Fig.1, where locations of these
samples are indicated by numbers 1, 3, and 5. The
samples were exposed during the whole 3rd campaign with
main peculiarities of operating regimes described in [2]. It
is seen that the samples were fixed at very different
locations: #1 was positioned near the divertor region, #3 –
close the plasma border, and #5 – quite deeply in the
diagnostic port in the same poloidal cross section and in
the same plane as #1 (central plane). After samples were
removed from the vacuum vessel the reflectance was
again measured in the same way, and the surface of
samples were analyzed by several methods: Auger
electron spectroscopy (AES), ion backscattering
technique (RBS) using 1.5 MeV He+ ion beam, scanning
electron microscopy (SEM), profilometry, and
ellipsometry at the wavelength 632.8 nm.
The 3rd LHD experimental campaign is characterized by
the following peculiarities [2]: total number of main
discharges 104, half with H2 and half with He as working gas
when plasma was heated by the ECH (~0.55 MW), ICRF
(1.5 MW), and NBI (~4.5 MW) methods. Besides, glow
discharge cleaning (two anodes) with total time ~2300 hrs
was equally distributed between discharges with He and H2
backgrounds. The maximal stored energy reached during the
3rd campaign was ~0.88 GW. In comparison to the 2nd LHD
campaign the graphite tiles were installed in the divertor area
in such a way that the plasma of divertor flows did interact
with graphite targets only.
It was found that after exposure in LHD the reflectance
of all samples has changed from the identical initial level.
The change was not only in an absolute value but even in
the opposite directions, as is seen from data in Fig.2. The
reflectance of mirrors #1 and #5 dropped strongly as a
result of appearance of the contaminating films, which
could be easily seen in the white-dark photo of samples.
From spectral dependence of reflectance (Fig.2) one can
conclude that the film on the #5 sample is thicker than on
the #1 sample. At the same time, the reflectance of sample
#3 increased significantly (Fig.2). This latter fact we
entail with not full cleaning of all three mirrors before
they were installed inside the LHD vessel from
contamination by some organic film appeared due to
rinsing samples in an ultrasonic bath. The high level of
reflectance for mirror sample #3 was supported by very
high quality of surface as was supported by profilometry
measurements and by analyzing the SEM photos.
The composition of the contaminating films that
appeared on samples #1 and #5 was estimated using AES
and RBS data. On the surface of #1 sample the deposited
layer was found to consist mainly of C (~40 atomic %)
and Fe (~40 atomic %) but on the #5 sample – the only
contaminant registered was carbon (~90 atomic %) [2].
The surface of the sample #3 was free of carbon however
a small trace of heavier metal, possibly, copper was
registered by RBS.
The optical properties of film on sample #1 were
measured by ellipsometry at the wavelength 632.8 nm
within a simple approximation: a homogeneous film on
the SS substrate. As the n and k values of the SS substrate
the indices measured for the sample #3 were used. The
refraction and extinction indices of the deposit found with
such an approximation are n=2.5 and k=0.33, and the film
thickness was estimated as ~26 nm. For sample #5 similar
data could not be obtained because of very low
reflectance at the wavelength of measurement (see Fig.2).
To know more about properties of contaminating films on
samples #1 and #5 and of the quality of mirror surface
under the coatings, the cleaning of these films using the
low temperature deuterium plasma was provided. The
results of this experiment are presented in the next
section.
Problems of Atomic Science and Technology. 2002. № 5. Series: Plasma Physics (8). P. 39-41 39
3. CLEANING OF MIRRORS #1 AND #5
The plasma was produced by an electron cyclotron
resonance (ECR) discharge in deuterium in a double-
mirror magnetic configuration with maximal magnetic
field strength near 2 kG in magnetic mirrors and
magnetron frequency 2.375 GHz [3]. It was shown earlier
[1] that such plasma is very effective in cleaning the
carbon film deposited on metallic surface.
The samples were fixed at the water-cooled holder
centered along the device axis and brought into the
discharge chamber through a vacuum shutter. The
magnetic field lines cross samples along the surface
normal. The electron density and temperature of plasma
in the region of the holder position was near 6⋅109 cm-3
and 3-5 eV, correspondingly, according to measurements
by electrostatic probes. Before and after cleaning of the
contaminating film both samples were weighed within
accuracy 20 mg. The cleaning procedure was carried out
step by step, with regular ex situ control of the spectral
reflectance in the wavelength range 220-650 nm. For
these particular samples two regimes of film cleaning
were applied: (i) without biasing the holder (like in [1]),
i.e., when during first 130 for sample #1 and 140 min for
sample #3 the ion energy was defined by the sheath
potential only, e.g., not exceeded ~15 eV and thus the
chemical erosion was the main mechanism of removing
the carbon-based film; (ii) with biasing holder to –300 V,
e.g., when starting from 130 min for #1 sample and from
140 min for #5 sample the ion energy much exceeded the
threshold of the physical sputtering of carbon and any
other contaminant material.
After 10-minute exposure during the (i)-cleaning
regime the mirror #5 became of a violet color instead of
initial dark-brown one, but the initial color returned back
when cleaning was continued. The color of the sample #1
did not change significantly during practically whole time
of cleaning.
The time dependences of reflectance recovering at two
wavelengths for both samples are shown in Fig.3. These
data demonstrate that the characteristics of films that
appeared on these samples are very different. Namely, the
film on the #5 sample was thicker (because the
interference effects are seen) but softer than the film on
the #1 sample. The rate of reflectance recovering by the
#5 sample during the cleaning regime (i) was much faster
in comparison to the #1 sample, however for both
samples the recovering was stopped after about one hour
cleaning time. For the #5 sample this “saturation” of
mirror recovering (in the time interval 60-140 min) is
probably due to full disappearance of the carbon film
deposited inside the LHD vessel, and the remained film
was the one connected with washing the sample in an
ultrasound bath after the finish of polishing. This lowest
contaminating layer was gradually disappearing, starting
from the time 140 min. For the #1 sample the
intermediate saturation level behaved in the way like the
rest film consisted of not one but two layers: the upper
which disappeared by ion bombardment during 130-145
min was probably the rest of the layer deposited in LHD,
and the lower one which had the thickness and
composition similar to the layer that maintained on the #5
sample due to washing in an ultrasound bath. The full
recovering of the spectral reflectance was achieved for
both samples after about 60 min bombardment by 300 eV
energy ions.
4. DISCUSSION AND CONCLUSION
The data obtained at this stage of experiment
demonstrate that the location of the mirror samples inside
the LHD vacuum chamber is very important factor
determining the rate of mirror degradation. The mirror #3
located close to the plasma confinement volume and quite
distant from the divertor regions was cleaned from the
contaminating film that appeared as a result of rinsing
samples in the ultrasound acetone bath and profilometry
and SEM data show that it saved the very smooth surface.
Mirror #1, fixed close to the divertor region with graphite
tiles as the divertor plates, became coated by the film of
complicated composition. The thickness of deposited
films found by AES and ellipsometry are not in
agreement each other. Namely, according to AES the
thickness was estimated as ~70 nm for #1 and ~700 nm
for #5 but only ~26 nm from ellipsometry data for #1
sample. The carbon film thickness on the mirror #5, fixed
deeply in the port, was much thicker according to optical
measurement (Fig.2) and results of cleaning (Fig.3)
however it could not be measured by ellipsometry, as was
mentioned above.
The values of n and k indices found for deposit on
sample #1 within the framework of the simple model (i.e.,
n=2.5, k=0.33) are in a quite good correspondence with
values characteristic for a carbon film that was evaporated
by an arc discharge between two graphite electrodes
(n=2.6, k=0.35 [1]) but very different from indices
measured for the film grown on the window of the JT-
60U tokamak (n=1.8-2.0, k=0.17-0.15 [4]).
The resistance of deposited films to impact of low
energy D ions is quite different as data of Fig.3 show. The
cleaning process demonstrates that the film on the #1
sample was significantly harder than that on the sample
#5. This is probably the result of high percentage of iron
in the composition of the deposit. The SEM photos
demonstrated that the film on the #5 sample was strongly
inhomogeneous compare to the quite homogeneous film
surface on the #1 sample.
After finishing the cleaning procedure the reflectance
spectral dependence of both mirrors became very close to
what is shown in Fig.2 by squares as an example of
typical SS mirror which was polished, rinsed in an
ultrasound bath, and cleaned by low energy deuterium
ions.
The mechanism which provided the cleaning of the
sample #3 from the initial contaminating film and the
maintenance of a high surface quality with corresponding
high reflectance was not understood yet.
Basing on the above described results we can make the
following conclusion:
The correct choice of mirror location inside the LHD
vacuum chamber with graphite tiles protecting the vessel
wall in the divertor area is a quite responsible problem. It
is evident that the mirror fixed at the same position as the
sample #3 will maintain its optical properties for a long
period of LHD operation. Such mirrors can be used for
observation of those parts of plasma or inner surfaces
40
(e.g., divertor plasma, divertor plates) that are not seen
directly through the diagnostic ports.
In the case of inappropriate choice of the mirror
position the cleaning of contaminating carbon-based
deposit on the mirror surface can become a quite difficult
problem because the biasing of the mirror holder to
several hundred volts would be required.
The behavior of mirrors in conditions when the
boronization procedure is planned to be used in future
experiments would be very desirable.
Fig.1. The scheme of locations of SS mirror samples
inside the LHD vessel.
0
10
20
30
40
50
60
70
200 300 400 500 600 700
R
ef
le
ct
an
ce
, %
Wavelength, nm
initial
#5
#1
#3
Fig. 2. Spectral reflectance of SS samples before (marked
as “initial”) and after exposure inside the LHD vessel
(curves marked as #1, #3, and #5). Squares show the
typical behavior of reflectance of a SS mirror subjected to
cleaning by low temperature deuterium plasma after
polishing and washing in an ultrasonic acetone bath.
0
10
20
30
40
50
60
70
0 50 100 150 200
R
ef
le
ct
an
ce
, %
Exposure time, min
650nm
220nm
#1
#5
#5
#1
Fig.3. The recovery of reflectance (normal incidence,
wavelengths 220 nm and 650 nm) of samples #1 and #5
due to deuterium ion bombardment. Up to t=130 min for
sample #1 and up to t=140 min for sample #5 the sample
holder was grounded, i.e., the energy of ions was <15eV.
After that times the samples were exposed to ions
accelerated to ~300 eV because of negatively biased
holder.
REFERENCES
1. V.Voitsenya, A.E.Costley, V.Bandourko et al.
Diagnostic first mirrors for burning plasma experiments.
Rev. Sci. Instr. 72 (2001) 475.
2. T.Hino, Y.Nobuta, Y.Yamauchi et al. Analysis for
surface probes of 3rd experimental campaign in the Large
Helical Device. Paper P1-28 at the PSI-15 Conference,
May 2002, Gifu, Japan.
3. A.F.Bardamid, V.T.Gritsyna, V.G.Konovalov et al. Ion
energy distribution effects on degradation of optical
properties of ion-bombarded copper mirrors. Surface and
Coatings Technology, 100-104 (1998) 365.
4. H.Yoshida. Private communication.
41
REFERENCES
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