Effect of the low energy ion bombardment on the optical properties of metallic mirrors
Schemes of several methods of plasma diagnostics in ITER in a high degree must be based on utilization of the reflective optics. In this connection there appeared the problem of the first mirrors (FM), i.e., mirrors directed to plasma under investigation. The FMs will be subjected to bombardment by...
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| Cite this: | Effect of the low energy ion bombardment on the optical properties of metallic mirrors / V. Bandourko, N. Kishimoto, V.A. Kurnaev, K. Nakamura, T. Sugie, V.S. Voitsenya // Вопросы атомной науки и техники. — 2000. — № 3. — С. 99-101. — Бібліогр.: 14 назв. — англ. |
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Bandourko, V. Kishimoto, N. Kurnaev, V.A. Nakamura, K. Sugie, T. Voitsenya, V.S. 2015-05-29T07:33:11Z 2015-05-29T07:33:11Z 2000 Effect of the low energy ion bombardment on the optical properties of metallic mirrors / V. Bandourko, N. Kishimoto, V.A. Kurnaev, K. Nakamura, T. Sugie, V.S. Voitsenya // Вопросы атомной науки и техники. — 2000. — № 3. — С. 99-101. — Бібліогр.: 14 назв. — англ. 1562-6016 https://nasplib.isofts.kiev.ua/handle/123456789/82376 533.9 Schemes of several methods of plasma diagnostics in ITER in a high degree must be based on utilization of the reflective optics. In this connection there appeared the problem of the first mirrors (FM), i.e., mirrors directed to plasma under investigation. The FMs will be subjected to bombardment by charge exchange atoms (CXA) and to deposition of contaminating materials. The CXA energy distribution will be very different for different mirrors, namely, it will be much higher with long tail in the case of mirrors for the core plasma than for mirrors in the divertor region. In this paper we present some results of investigations of effect of the long-term bombardment by deuterium ions with sub- or near-threshold energy on reflectance of metallic mirrors. en Національний науковий центр «Харківський фізико-технічний інститут» НАН України Вопросы атомной науки и техники Рlasma Dynamics and Plasma-Wall Interaction Effect of the low energy ion bombardment on the optical properties of metallic mirrors Article published earlier |
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Effect of the low energy ion bombardment on the optical properties of metallic mirrors |
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Effect of the low energy ion bombardment on the optical properties of metallic mirrors Bandourko, V. Kishimoto, N. Kurnaev, V.A. Nakamura, K. Sugie, T. Voitsenya, V.S. Рlasma Dynamics and Plasma-Wall Interaction |
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Effect of the low energy ion bombardment on the optical properties of metallic mirrors |
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Effect of the low energy ion bombardment on the optical properties of metallic mirrors |
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Effect of the low energy ion bombardment on the optical properties of metallic mirrors |
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Effect of the low energy ion bombardment on the optical properties of metallic mirrors |
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effect of the low energy ion bombardment on the optical properties of metallic mirrors |
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Bandourko, V. Kishimoto, N. Kurnaev, V.A. Nakamura, K. Sugie, T. Voitsenya, V.S. |
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Bandourko, V. Kishimoto, N. Kurnaev, V.A. Nakamura, K. Sugie, T. Voitsenya, V.S. |
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Рlasma Dynamics and Plasma-Wall Interaction |
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Рlasma Dynamics and Plasma-Wall Interaction |
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2000 |
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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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Schemes of several methods of plasma diagnostics in ITER in a high degree must be based on utilization of the reflective optics. In this connection there appeared the problem of the first mirrors (FM), i.e., mirrors directed to plasma under investigation. The FMs will be subjected to bombardment by charge exchange atoms (CXA) and to deposition of contaminating materials. The CXA energy distribution will be very different for different mirrors, namely, it will be much higher with long tail in the case of mirrors for the core plasma than for mirrors in the divertor region. In this paper we present some results of investigations of effect of the long-term bombardment by deuterium ions with sub- or near-threshold energy on reflectance of metallic mirrors.
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1562-6016 |
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https://nasplib.isofts.kiev.ua/handle/123456789/82376 |
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Effect of the low energy ion bombardment on the optical properties of metallic mirrors / V. Bandourko, N. Kishimoto, V.A. Kurnaev, K. Nakamura, T. Sugie, V.S. Voitsenya // Вопросы атомной науки и техники. — 2000. — № 3. — С. 99-101. — Бібліогр.: 14 назв. — англ. |
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2025-11-26T14:05:31Z |
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UDC 533.9
Problems of Atomic Science and Technology. 2000. N 3. Series: Plasma Physics (5). p. 99-101 99
EFFECT OF THE LOW ENERGY ION BOMBARDMENT ON THE OPTICAL
PROPERTIES OF METALLIC MIRRORS
V.Bandourkoa,b, N.Kishimotoa, V.A.Kurnaevb, K.Nakamurac, T.Sugiec, V.S.Voitsenyad
aNational Research Institute for Metals 1-2-1, Sengen, Tsukuba, Ibaraki 305, Japan
bMoscow State Engineering Physics Institute, Kashirskoe sh. 31, Moscow 115409, Russia
cJapan Atomic Energy Research Institute, Naka-machi, Ibaraki-ken, 311-0193, Japan
dInstitute of Plasma Physics, National Science Center “Kharkov Institute of Physics & Technology”
Kharkov 61108, Ukraine
Schemes of several methods of plasma diagnostics in ITER in a high degree must be based on utilization of the reflective
optics. In this connection there appeared the problem of the first mirrors (FM), i.e., mirrors directed to plasma under
investigation. The FMs will be subjected to bombardment by charge exchange atoms (CXA) and to deposition of contaminating
materials. The CXA energy distribution will be very different for different mirrors, namely, it will be much higher with long tail
in the case of mirrors for the core plasma than for mirrors in the divertor region. In this paper we present some results of
investigations of effect of the long-term bombardment by deuterium ions with sub- or near-threshold energy on reflectance of
metallic mirrors.
1. Introduction
The employment of the plasma facing mirror is
requisite for the plasma diagnostic systems of the
present large-scale fusion devices and future
experimental fusion reactor. Even though these
mirrors are located far away from the hot plasma,
they are bombarded with charge exchange atoms
(CXA) that lead to the surface modification due to
erosion, redeposition and implantation of hydrogen
isotopes. There are only few data relating the change
of the optical properties of mirror materials due to
CXA-bombardment in fusion devices under
operation. In [1] the lifetime prediction for mirrors
used in ITER has been estimated based on the
observed surface modification and the reflectivity
change of carbon, aluminum and nickel samples
exposed to the JET plasma taking into account the
energy distribution of the CXA-flux measured at
ASDEX-U [2-5]. In that estimation for an incident
flux with an energy distribution Ã(E) an effective
sputtering yield Yeff was defined by
Yeff= (1/Γtot)∫ Y(E) Γ(E) dE,. (1)
Here Ãtot is the total incident flux, Γtot = ∫ Γ(E)dE and
Y(E) is the energy dependent sputtering yield taken
from [6] where data for sputtering of mono-species
were reported. It should be noted that with such an
approach, a contribution of atoms with energy below
the threshold energy is automatically neglected,
while the lower energy component of CXA-flux is
orders of magnitude higher with respect to the
amount of high energy atoms [1]. In the case of the
first mirrors for diagnosing the divertor plasma, the
CXA flux will probably not contain high energy
atoms. However, even with a projectile energy
below the threshold for sputtering, some kinds of
defects can be produced in the near-surface layer of
mirrors. For example, the cluster formation in Mo
was demonstrated under bombardment by hydrogen
atoms with energy below the sputtering threshold [7].
As another example of importance of the low energy
projectiles, there is the experimental evidence that the
presence of only 0.1% oxygen atoms in the deuterium
flux results in reducing the effective threshold energy
for W from 341 eV [6] down to 44.5 eV [8] or 20-150
eV [9]. The objective of present study is to simulate the
behavior of the first mirrors for the divertor plasma
(DFM) and to evaluate the optical degradation of the
mirror caused by low energy deuterium bombardment,
which allows to complement the early papers [10-13] on
the influence of fusion reactor conditions on optical
properties of plasma-viewing mirrors.
2. Experimental
The experiments were carried out with the super low
energy particle irradiation system (SLEIS) [14] where a
high density ion beam at low energies can be formed.
The species of charged particles with acceleration
voltage of 200V were analyzed by means of a magnetic
mass analyzer). Under a certain gas pressure and arc
power, ~83.5% of the total charged particles were
extracted as D3
+ ions and ~14% as D+ ions. Also ~2.5%
of impurity ions, mostly oxygen, have been detected.
This means that ~94%, ~5% and ~1% in the total flux
were deuterons with energy 67eV and 200eV, and
impurity ions, respectively. The fluence of each incident
species is calculated from measured ion beam current
and known composition of the ion beam. A test sample
was placed about 10 cm downstream from the ion
source. The temperature of the sample was measured by
thermocouples during irradiation (< 80oC for all the
irradiated targets). Mirrors of Mo (22 mm in diameter, 3
mm thickness), SS No1 (22 mm in diameter, 3 mm
thickness), and SS No2 (22×22×4 mm3) were prepared
by mechanical polishing, and a diamond-turned Cu
mirror (22×22×4 mm3) was manufactured of an oxygen-
free material. The reflectance R(λ), for the wavelengths
100
λ = 190-2500 nm and the target weight change ∆m
were measured, reproducibility, using a standard
monochromator with reproducibility of ∼1% and the
Mettler AE240 microbalance with an absolute
accuracy 0.01 mg, after step by step exposures of
mirrors to the ion beam. In the case of SS mirrors all
the surface area was irradiated whereas a Mo
diaphragm (0.5 mm thickness) with a 8 mm hole in
diameter was placed at 1 mm above the Mo and Cu
mirrors, that allows to compare a reflectivity of
irradiated and unirradiated areas of the same mirror
after every exposure.
3. Results and discussion
The effective sputtering yields determined by the
mass loss method for deuterium ions bombardment
of Mo, Cu and SS samples are compared in Fig.1
and Table 1 with those calculated using data from
[6]. Effects of impurity ions were neglected in the
calculation.
Fig.1. Comparison of calculated and measured
effective sputtering yields in atoms per one thousand
of projectiles (D atoms). The sputtering data from
ref. [6] were used for the calculations.
Good agreement between experimentally obtained
and calculated data indicates that the physical
sputtering of mirror materials due to deuterium ions
dominates the erosion process. Since the energy of
94% of total incident deuterium ions is below the
threshold energy for Mo sputtering, the estimated
thickness of the sputtered layer is the lowest for the
Mo mirror (4.1×10-8 m) and increases up to 0.2×10-6
m for the Cu mirror. It is considered that the
decrease of the reflectivity of eroded mirrors is due
to development of surface roughness during
sputtering or/and change of chemical composition of
the near-surface region, e.g., by deposition of a thin
layer of contaminants, i.e., materials of cathode, W,
or accelerating grids, Mo.
As was shown in [1], the mean surface roughness of
an Al layer on the carbon substrate increased
approximately linearly with increasing thickness of
sputtered layer. The maximum thickness of sputtered
layer reached ~400nm and the corresponding CXA
fluence was estimated to be ~2.5⋅1024at/m2, i.e.,
several times smaller than that typical for the present
experiments. If one assumes the proportionality of
surface roughness to the thickness of sputtered layer,
like in [1], then the mean roughness of the Mo mirror
would be of the order 40 nm, as follows from Table 1.
The surface microrelief of such size, principally, could
be responsible for the small decrease of Mo mirror
reflectance that was observed. However, in the case of
SS1 mirror a significant improvement of reflectance
was found after layer of about factor two thicker was
sputtered, (Table 1 and Fig.2). The mirror SS2 behaved
very similar to SS1 being bombarded at incident angle
45°. Therefore, the microrelief developing on the mirror
surface cannot play a significant role in our experiments
with low energy projectiles.
The improvement of specular reflectance of stainless
steel mirrors due to long-term bombardment with low
energy deuterium ions is not fully understood yet.
However the role of deposit of cathode (W) or grids’
(Mo) materials of the ion source have to be excluded as
the reflectance of these metals in visible and near-
visible regions, where the highest increment of SS
mirror reflectance was observed, is lower than
reflectance of SS mirrors tested (Fig.2). Thus, the
improvement of reflectance should be prescribed to
Fig.2. Reflectance of Mo (solid lines) and SS (dashed
lines) mirrors. Closed symbols – before ion
bombardment, open symbols – after ion fluences of
9.1⋅1020D/cm2 for Mo and 7.4⋅1020D/cm2 for SS mirrors,
correspondingly.
modification of the surface of SS mirrors. Between
possible reasons the following ones are most probable:
(i) cleaning from the uncontrolled contaminants,
including an oxide film, (ii) change of the surface
composition, i.e., faster sputtering of that SS component
that has the lowest reflectivity, and (iii) additional
polishing of the surface by low energy deuterium ions.
It was demonstrated for mirrors of different
polycrystalline materials that sputtering of the same
thickness of a near-surface layer resulted in different
degradation rate of the optical properties [12]. The
mirrors fabricated of the same stainless steel as in
0
1
2
3
4
5
6
7
8
0 1 2 3 4 5 6 7 8
Ef
fe
ct
iv
e
sp
ut
te
rin
g
yi
el
d,
at
/1
00
0
D
a
t
Calculated sputtering yield, at/1000 D at
Mo
SS
Cu
30
40
50
60
70
200 400 600 800 1000
R
ef
le
ct
an
ce
, %
Wavelength, nm
Mo
SS
101
present experiments (i.e., the 316 type) demonstrated
a quite high survivability in maintaining the optical
properties in comparison to mirrors of several other
metals (Be, Al, Cu). And what is important, it was
shown at least, for two metals, Cu and SS, that the
rate of reflectance degradation strongly decreased
with decreasing the ion energy [10,13]. As distinct
from our experiments, however, in works [10-13]
the accelerating voltage was varied in the range
0.35-1.5 kV, i.e. the mean energy of projectiles
exceeded the sputtering threshold even for such
metals as Mo and W. That is why the results of
simulation experiments [10-13] cannot be used
directly for shedding light on the better
understanding of results obtained in the present
paper.
With small sputtering rate which will be
characteristic for DFM operation, the appearance of
deposit on the DFM surface probably cannot be
avoided, as it follows from results of some
presentations from ASDEX, D-IIID, and JET at the
last PSI conference (May 2000, Rosenheim,
Germany). In particular, it was found that in the
divertor region the rate of growth of the carbon
deposit could be as high as 3 nm/s. Therefore, the
effects of contamination of DFM surfaces have to be
investigated in simulation experiments in addition to
effects of sputtering by low energy hydrogen
(deuterium) atoms.
4. Conclusion
It is thus concluded from the optical measurement
and theoretical evaluation that low-energy CXA
bombardment of the first diagnostic mirrors for a
divertor plasma in a fusion reactor will not lead to
serious degradation of DFM optical properties. Much
stronger effects on the DFM reflectance will probably
occur due to deposition of contaminants such as carbon
if collector plates are fabricated of the carbon-carbon
composite, as is planned now. Therefore the special
simulation experiments at the nowaday tokamaks with
divertor (JET, JT-60U, TEXTOR, D-IIID) have to be
provided.
References
[1] M.Mayer, et al. In: Diagnostics for Experimental
Thermonuclear Fusion Reactor 2, Edit. by Stott et al.,
Plenum Press, New York, 1998, p. 279.
[2] H.Verbeek and the ASDEX-team, J.Nucl. Mater.
145-147 (1987) 523.
[3] H.Verbeek, J. Phys. E 19 (1986) 964.
[4] H.Verbeek, et al. J.Nucl.Mater.196-198(1992) 1027.
[5] H.Fahrbach, et al. Proc. 16th EPS Conf. Controlled
Fusion and Plasma Physics, Vol. 13B (1989) p. 1537
[6] W. Eckstein et al. Sputtering Data, Report IPP 9/82,
Max-Planck-Institut fur Plasmaphysik, Garching, 1993.
[7] R.Sakamoto, T.Muroga and N.Yoshida, J. Nucl.
Mater. 212-215 (1994) 1426.
[8] Y.Hirooka, J. Nucl. Mater. 258-263 (1998) 1045.
[9] N.V.Antonov, B.I.Khripunov, V.B.Petrov, et al. J.
Nucl. Mater. 220-222 (1995) 943.
[10] A.F.Bardamid et al., Surf. & Coating Technol. 103-
104 (1998) 365.
[11] V.S.Voitsenya, V.I.Gritsyna, V.T.Gritsyna et al.,
Fusion Eng. Design, 34-35 (1997) 365.
[12] V.S.Voitsenya et al. Rev. Sci. Instr. 70 (1999) 790.
[13] ] A.F.Bardamid et al. Vacuum 58 (2000) 7.
[14] K.Nakamura, M.Dairaku, M.Akiba, Y. Okumura, J.
Nucl. Mater, 241-243 (1997) 1142.
Table 1. Material properties and calculated and measured sputtering data in the present experiment.
The mirrors SS1 and SS2 were irradiated at incident angles of 0o and 45o respectively.
___________________________________________________________
M2 ρ Eth [6] Yeff [6] Yeff Φ ∆m h
g/mol g/cm3 eV 10-3 at/D 10-3 at/D 1024 D/m2 10-3g µm
______________________________________________________________________
Mo 96 10.2 77 0.15 0.24 4.15 0.03 -
9.1 -0.02 0.041
12.7 -0.03 0.058
______________________________________________________________________
SS1 55.1 7.45 39 1.47 1.28 2.57 -0.11 0.039
7.42 -0.23 0.081
11.5 -0.51 0.180
______________________________________________________________________
SS2 55.1 7.44 39 - 3.15 2.6 -0.37 0.100
7.46 -1.04 0.290
11.8 -1.63 0.450
______________________________________________________________________
Cu 64 8.93 32 7.67 6.65 2.08 -0.05 0.110
3.33 -0.09 0.200
7.47 -0.26 0.580
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