Effect of thin contaminating coating on reflectance of metallic mirror placed inside the vacuum chamber of a fusion device
The practice of use of diagnostic mirrors inside the fusion devices revealed the appearance of a deposit on the mirror surface. Such deposit is a result of condensation of the erosion materials of those inner components that are subjected to the strongest plasma impact. Another reason for deposit gr...
Saved in:
| Published in: | Вопросы атомной науки и техники |
|---|---|
| Date: | 2000 |
| Main Authors: | , , , , , , |
| Format: | Article |
| Language: | English |
| Published: |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України
2000
|
| Subjects: | |
| Online Access: | https://nasplib.isofts.kiev.ua/handle/123456789/82385 |
| Tags: |
Add Tag
No Tags, Be the first to tag this record!
|
| Journal Title: | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| Cite this: | Effect of thin contaminating coating on reflectance of metallic mirror placed inside the vacuum chamber of a fusion device / V.N. Bondarenko, A.F. Bardamid, V.G. Konovalov, V.S. Voitsenya, D.V. Orlinskij, L.V. Poperenko, M.V. Vinnichenko // Вопросы атомной науки и техники. — 2000. — № 3. — С. 64-66. — Бібліогр.: 14 назв. — англ. |
Institution
Digital Library of Periodicals of National Academy of Sciences of Ukraine| _version_ | 1860028979473285120 |
|---|---|
| author | Bondarenko, V.N. Bardamid, A.F. Konovalov, V.G. Voitsenya, V.S. Orlinskij, D.V. Poperenko, L.V. Vinnichenko, M.V. |
| author_facet | Bondarenko, V.N. Bardamid, A.F. Konovalov, V.G. Voitsenya, V.S. Orlinskij, D.V. Poperenko, L.V. Vinnichenko, M.V. |
| citation_txt | Effect of thin contaminating coating on reflectance of metallic mirror placed inside the vacuum chamber of a fusion device / V.N. Bondarenko, A.F. Bardamid, V.G. Konovalov, V.S. Voitsenya, D.V. Orlinskij, L.V. Poperenko, M.V. Vinnichenko // Вопросы атомной науки и техники. — 2000. — № 3. — С. 64-66. — Бібліогр.: 14 назв. — англ. |
| collection | DSpace DC |
| container_title | Вопросы атомной науки и техники |
| description | The practice of use of diagnostic mirrors inside the fusion devices revealed the appearance of a deposit on the mirror surface. Such deposit is a result of condensation of the erosion materials of those inner components that are subjected to the strongest plasma impact. Another reason for deposit growth is the wall conditioning procedures like carbonization and boronization. Appeared on the diagnostic mirrors and windows the contaminating films deteriorate the optical properties of these diagnostic elements, i.e., the mirror reflectance and window transmissivity. The object of this paper is to investigate an influence on reflectance of metal mirrors of thin films of the materials that are most probable in fusion devices under operation (boron and carbon) or can be promising in a fusion reactor (beryllium).
|
| first_indexed | 2025-12-07T16:51:02Z |
| format | Article |
| fulltext |
UDC 533.9
Problems of Atomic Science and Technology. 2000. N 3. Series: Plasma Physics (5). p. 64-66 64
EFFECT OF THIN CONTAMINATING COATING ON REFLECTANCE OF
METALLIC MIRROR PLACED INSIDE THE VACUUM CHAMBER OF A
FUSION DEVICE
V.N. Bondarenko, A.F. Bardamid1, V.G. Konovalov, V.S. Voitsenya, D.V. Orlinskij2,
L.V. Poperenko1, M.V. Vinnichenko1
IPP NSC KIPT, Kharkov 61108, Ukraine;
1Kiev National University, Kiev 01033, Ukraine;
2Kurchatov Institute, Moscow, Russia
The practice of use of diagnostic mirrors inside the fusion devices revealed the appearance of a deposit on the
mirror surface. Such deposit is a result of condensation of the erosion materials of those inner components that
are subjected to the strongest plasma impact. Another reason for deposit growth is the wall conditioning
procedures like carbonization and boronization. Appeared on the diagnostic mirrors and windows the
contaminating films deteriorate the optical properties of these diagnostic elements, i.e., the mirror reflectance and
window transmissivity. The object of this paper is to investigate an influence on reflectance of metal mirrors of
thin films of the materials that are most probable in fusion devices under operation (boron and carbon) or can be
promising in a fusion reactor (beryllium).
1. Introduction
The widespread application of low-Z materials for
the first wall protection in nowaday fusion devices is
caused by an objective to reduce the metal atom influx
from the vessel walls into the plasma and to improve
the discharge performance. Since carbonization on
tokamak TEXTOR had successful result [1], this
method became a usual procedure in many fusion
devices. The idea to use boron based films [2] for
coating the internal surfaces like inner walls and
structures was tested for the first time on the same
facility. Today the boronization procedure is used
practically in all experiments at the more or less large-
scale fusion devices together with the graphite
protection for those first wall areas, which are
subjected to the strongest plasma impact. Thus, the
deposit appearing on all inner surfaces of vacuum
chamber is the carbon-boron-based film. It was found
that the definite portion of hydrogen [3] is accumulated
inside the boron-carbon film deposited on the inner
surfaces of a fusion device. On the remote inner
components, like mirrors and windows, the film has to
grow not only during boronization process, but during
the working discharges also [2, 4]. The experimental
data on transmissivity of a deposit grown on windows
of TFTR and JT-60U tokamaks during the campaign
when carbonization was regularly used are presented in
papers [5, 6]. It was determined in [6] that deposited
film has chemical composition of the
polyacrylonitrile type. As follows from the literature,
up to now there were no publications devoted to the
topic of the deposit influence on reflectance of mirrors
situated inside the chamber of a fusion device. The aim
of this paper is to investigate the deposit role in the
degradation of optical properties of the in-vessel
mirrors. The main our interests are around a subject of
boron-carbon films, which do frequently appear in the
large-scale fusion devices. In addition, the effect of
thin beryllium film deposited on the surface of metal
mirror is analyzed because of the prospect for this
material to be chosen as a protection of the first wall in
a fusion reactor. The studied wavelength range is 200-
1000 nm that is of practical interest for plasma
diagnostics in fusion devices under operation.
2. Effect of thin film on specular reflectance
(experiment and calculation)
The equations for the effective reflectance of the
metal mirror coated with thin partly-transparent film of
any given thickness, d, with known refraction n(λ) and
absorption k(λ) optical indices of the substrate and the
film are represented in [7]. In present work we have
applied more practical relationships from [8], which
gives the effective reflectance of the metal mirror
coated with thin partly transparent film at the normal
incidence of light. The optical indices of films and
substrates were obtained from the ellipsometric
measurements and from the literature [9].
The film optical properties depend on conditions of
deposition. For example, the contaminating carbon-
based film on the diagnostic window of JT-60U [6] has
the indices n=1.8-2.0, k=0.15-0.17 measured at the
wavelength of the He-Ne laser (632.8 nm). These data
are different from the values n=2.63, k=0.35 [10]
determined for arc-evaporated carbon film at the same
wavelength.
In our experiments, the spectral dependences of
optical indices for the substrates (stainless steel, SS,
and molybdenum), for the carbon films deposited on
these substrates due to the arc discharge between two
graphite electrodes, and the film thickness, were all
determined from the ellipsometric measurements. In
the SS substrate case the carbon films were of d=11
65
and 21 nm thick. The measured n and k values for these
films were not too different as compared with data
presented in work [10]. The differences for n and for k
values were found to be maximal (~14%) near the
lowest wavelength, while for the visible light n and k
values differed on ~5%. It could be a consequence of
similarity of film deposition methods (arc discharge
between graphite electrodes) in paper [10] and in our
research.
The comparison of measured spectral reflectance,
R(λ), at normal light incidence and R(λ) calculated by
means of the equation [8], using n and k values
measured and taken from [10], is shown in Fig.1.
One could observe that the agreement between
calculated data and results of measurements is quite
reasonable almost in the whole spectral range where
experiments were carried out. The Fig.1 demonstrates
that the carbon film of the order of 10 nm in thickness
caused the strong degradation of reflectance of the SS
mirror. The result obtained with this coating should be
comparable qualitatively with the result of any other
metal mirror coated with a carbon-based film of the
same thickness.
Molybdenum is one of the candidate materials for
the in-vessel first mirrors in a future fusion reactor. It
possesses a low sputtering yield and has a rather high
reflectance in the range of interest for plasma
diagnostics. That is why the effect of contamination of
molybdenum mirror by a carbon film of different
thickness was studied by similar procedure as SS
mirror. Three sectors of the molybdenum mirror
(diameter 22 mm) were coated by carbon layers of
thickness d=23, 35 and 56 nm in similar conditions as
the SS mirror. One sector of Mo mirror remained free
of coating. The n and k values determined by
ellipsometry for the first carbon film (d=23 nm) were
slightly different from those for the second film (d=35
nm), probably because of film structure modification
when its thickness is increasing.
For the thickest film, the ellipsometric
measurements were problematic due to low reflection
and optical indices were taken as average values
measured for thinner films. The molybdenum optical
indices obtained by the ellipsometric technique were
used for calculation of the R(λ) dependence shown in
Fig.2 as solid line (upper curve) along with reflectance
measured at normal
incidence (open circles and dotted line). Graphs of
R(λ) calculated for the coated parts are plotted by solid
lines with solid markers. The measured reflectance
values for the same Mo sample areas are shown as the
dotted lines with open markers.
Quite reasonable qualitative agreement between
measured and calculated values of reflectance is
observed again. For the film of 23 nm thick, there is
also quite good quantitative agreement, i.e., the average
difference between calculated and measured values is
approximately 5%. For thicker films (35 nm or 56 nm)
the difference in absolute meanings of calculated and
measured R values is high enough, however,
qualitatively the behavior of dependences remains
similar. It could be inferred that increase of difference
between the measured and the calculated R values with
increasing film thickness is associated with
inhomogeneity of the film along the mirror surface.
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
300 400 500 600 700 800
C on SS
R
ef
le
ct
an
ce
Wavelength, nm
SS
d=11 nm
d=21 nm
Fig.1. C film on SS mirror. The spectral reflectance:
the dotted lines (calculated from [10]) and the solid
lines (calculated from ellipsometry). The points (X, �)
present measured reflectance. The thickness of film is
marked near every group.
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
300 400 500 600 700 800
C on Mo
R
ef
le
ct
an
ce
Wavelength, nm
C on Mo
Mo
23 nm
36 nm
56 nm
Fig.2. The spectral reflectance for C film on Mo
mirror. Solid lines and solid data markers
represent the results of calculations while the
dotted lines with open markers depict the
corresponding measured data. The film thickness
is marked near every group.
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
200 300 400 500 600 700 800 900 1000
B, C, Be on Rh
Rh
B (20 nm) on Rh
C (20 nm) on Rh
Be (10 nm) on Rh
Be (20 nm) on Rh
Wavelength, nm
R
ef
le
ct
an
ce
Fig.3. The calculated spectral reflectance values of
clean and contaminated Rh mirror. Each
combination is marked near the related curve.
66
Rhodium as well as Mo is a prospect material for
the first mirrors of plasma diagnostics in ITER [11],
therefore the effect of contamination of rhodium
mirror is of great interest. The curves of Fig. 3
indicate the spectral reflectance calculated for the
most probable contaminating films (Be, C, B) of 20 nm
thick.
The optical indices for Rh and Be were taken from
[9], the carbon and boron indices were determined by
ellipsometric measurements. Since the metallic films
have higher absorption index than C and B films, the
appearance of Be film leads to much stronger changes
of reflectance for any metallic substrate. In the case of
Be layer, the dependence R(d) shows that Be coating
with thickness d ≥ 20 nm on any metal substrate has
R(λ) behavior the same as bulk beryllium mirror.
3. Discussion
The results obtained show the strong influence of
the deposition of thin (≥ 10 nm) boron-carbon film on
the effective reflectance of a metal mirror in the
visible and in the nearest UV ranges. The film appeared
on the in-vessel mirror changes the mirror reflectivity
stronger than the transmissivity of diagnostic window
because of longer path of reflected light beam passing
through a film on the mirror. The rate of reflectance
change due to deposit growth depends on the light
wavelength, the chemical composition of film and its
thickness. Starting from the thickness d ≥ 35 nm for the
carbon layer on Mo substrate, the optical properties of
the film become inhomogeneous across the film
coated surface. It is probably hard to predict the
variation of optical properties of film with increasing
the film thickness because new phases appear in the
film when it continues to grow.
A problem of carbon-boron deposit growth can be
effectively solved by methods of surface cleaning. For
the optical windows, the efficiency of chemical
cleaning by using the local ECR discharge in hydrogen
was demonstrated in [12], in addition to laser ablation
method [6,13,14]. For the in-vessel mirrors the
methods of the boron-carbon deposit removal were not
suggested yet.
4. Conclusions
−The reflectivity of mirrors and transmissivity of
windows depends in a high degree on the deposition of
thin contaminating films on their surfaces. The
thickness, the chemical and the structural composition
of such film has the strong influence on the reflectance
of mirror that also actually depends on wavelength of
an incident light.
−The adequate prediction of a final result of film
deposition on the mirror surface requires more
knowledge of film optical properties even with known
thickness. The data for films must be studied according
to variation of chemical and structural composition in a
wide range to follow the most probable composition in
fusion devices.
−The simple and reliable methods for the regularly
provided in-situ calibration and control of reflectance
of the in-vessel mirrors, as well as the methods of
deposits cleaning have to be developed. The plasma
properties of an ECR discharge in hydrogen (or
deuterium) look rather promising for both these
applications. However, the special experiments in
large-scale fusion devices have to be carried out to
optimize the characteristics of ECR discharge to solve
the problem of low Z material deposition on the
working characteristics of the in-vessel mirrors.
References
1. J.Winter, J. Nucl. Mater. 145-147, 14 (1987).
2. J.Winter, J. Nucl. Mater. 176-177, 14 (1990).
3. A.Annen et al., Thin Solid Films 312, 147 (1998).
4. V.S.Voitsenya, Sov. J. Plasma Phys. 17, 135
(1991).
5. D.H.McNeil, Rev. Sci. Instr. 61, 1263 1990).
6. H.Yoshida et al., JAERI-Research Report 96-062.
7. Max Born and Emil Wolf. Principles of Optics,
(Pergamon Press, 1975).
8. G.Hass, J. Opt. Soc. Am. 47, 1070 (1957).
9. Handbooks of optical constants of solids, edited by
Edvard D. Palik. Academic Press, Inc.,1985 and 1991.
10. E.T.Arakawa et al., Phys. Rev., 31, 8097 (1985).
11. Design Description Document (DDD) ITER
Diagnostic System (WB 5.5) Dec. 1997.
12. K.Okazaki et al., J. Nucl. Mater. 145-147, 761
13. K.Narihara et al., Rev. Sci. Instr. 63, 3527 (1992).
14. B.W.Brown et al., Rev. Sci. Instr. 66, 3077 (1995).
|
| id | nasplib_isofts_kiev_ua-123456789-82385 |
| institution | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| issn | 1562-6016 |
| language | English |
| last_indexed | 2025-12-07T16:51:02Z |
| publishDate | 2000 |
| publisher | Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| record_format | dspace |
| spelling | Bondarenko, V.N. Bardamid, A.F. Konovalov, V.G. Voitsenya, V.S. Orlinskij, D.V. Poperenko, L.V. Vinnichenko, M.V. 2015-05-29T07:57:56Z 2015-05-29T07:57:56Z 2000 Effect of thin contaminating coating on reflectance of metallic mirror placed inside the vacuum chamber of a fusion device / V.N. Bondarenko, A.F. Bardamid, V.G. Konovalov, V.S. Voitsenya, D.V. Orlinskij, L.V. Poperenko, M.V. Vinnichenko // Вопросы атомной науки и техники. — 2000. — № 3. — С. 64-66. — Бібліогр.: 14 назв. — англ. 1562-6016 https://nasplib.isofts.kiev.ua/handle/123456789/82385 533.9 The practice of use of diagnostic mirrors inside the fusion devices revealed the appearance of a deposit on the mirror surface. Such deposit is a result of condensation of the erosion materials of those inner components that are subjected to the strongest plasma impact. Another reason for deposit growth is the wall conditioning procedures like carbonization and boronization. Appeared on the diagnostic mirrors and windows the contaminating films deteriorate the optical properties of these diagnostic elements, i.e., the mirror reflectance and window transmissivity. The object of this paper is to investigate an influence on reflectance of metal mirrors of thin films of the materials that are most probable in fusion devices under operation (boron and carbon) or can be promising in a fusion reactor (beryllium). en Національний науковий центр «Харківський фізико-технічний інститут» НАН України Вопросы атомной науки и техники Мagnetic Confinement Effect of thin contaminating coating on reflectance of metallic mirror placed inside the vacuum chamber of a fusion device Article published earlier |
| spellingShingle | Effect of thin contaminating coating on reflectance of metallic mirror placed inside the vacuum chamber of a fusion device Bondarenko, V.N. Bardamid, A.F. Konovalov, V.G. Voitsenya, V.S. Orlinskij, D.V. Poperenko, L.V. Vinnichenko, M.V. Мagnetic Confinement |
| title | Effect of thin contaminating coating on reflectance of metallic mirror placed inside the vacuum chamber of a fusion device |
| title_full | Effect of thin contaminating coating on reflectance of metallic mirror placed inside the vacuum chamber of a fusion device |
| title_fullStr | Effect of thin contaminating coating on reflectance of metallic mirror placed inside the vacuum chamber of a fusion device |
| title_full_unstemmed | Effect of thin contaminating coating on reflectance of metallic mirror placed inside the vacuum chamber of a fusion device |
| title_short | Effect of thin contaminating coating on reflectance of metallic mirror placed inside the vacuum chamber of a fusion device |
| title_sort | effect of thin contaminating coating on reflectance of metallic mirror placed inside the vacuum chamber of a fusion device |
| topic | Мagnetic Confinement |
| topic_facet | Мagnetic Confinement |
| url | https://nasplib.isofts.kiev.ua/handle/123456789/82385 |
| work_keys_str_mv | AT bondarenkovn effectofthincontaminatingcoatingonreflectanceofmetallicmirrorplacedinsidethevacuumchamberofafusiondevice AT bardamidaf effectofthincontaminatingcoatingonreflectanceofmetallicmirrorplacedinsidethevacuumchamberofafusiondevice AT konovalovvg effectofthincontaminatingcoatingonreflectanceofmetallicmirrorplacedinsidethevacuumchamberofafusiondevice AT voitsenyavs effectofthincontaminatingcoatingonreflectanceofmetallicmirrorplacedinsidethevacuumchamberofafusiondevice AT orlinskijdv effectofthincontaminatingcoatingonreflectanceofmetallicmirrorplacedinsidethevacuumchamberofafusiondevice AT poperenkolv effectofthincontaminatingcoatingonreflectanceofmetallicmirrorplacedinsidethevacuumchamberofafusiondevice AT vinnichenkomv effectofthincontaminatingcoatingonreflectanceofmetallicmirrorplacedinsidethevacuumchamberofafusiondevice |