Aluminum oxide films are used as low refractive index layers in multilayer dielectric mirrors, which are expected to be used in ITER plasma diagnostic optical systems. In such mirrors, a film with a low refractive index is the outer layer. In addition to the normal operating modes of ITER, a number of emergency modes are assumed, one of which is the destruction of the water cooling system of the first wall, divertor or blanket. In this case, the vacuum chamber is filled with steam, the parameters of which depend on the location of the destruction and on the stage of operation of the reactor at which the accident occurs. The maximum steam parameters are set by a special system that limits the pressure to 150 kPa, and the maximum temperature of 250°C can be the case when an accident occurs during vacuum training of the chamber. The work examines the interaction of steam with amorphous films of aluminum oxide deposited on glass of the K-9 grades by reactive magnetron sputtering. It has been shown that exposure of a film 300 nm thick at a temperature of 250°C and a steam pressure of 150 kPa for 2 hours is accompanied by intense hydroxylation of the film and the transformation of the entire oxide film into hydroxides. This leads to severe degradation of light transmission, which may cause a change in the optical properties of the dielectric mirror. As a next step, similar steam exposures are planned of the mirrors in which with a low refractive index layers will alternate with layers of oxides with a high refractive index, such as hafnium, tantalum, and zirconium oxides.

Artificial polymer stones with different acrylate contents were studied by thermal desorption mass spectrometry and X-ray microanalysis. At temperatures below 100°C, acrylic and polyester artificial stones had approximately the same heat resistance. When the materials were heated above 100°C, their thermolysis products had different compositions. In addition to methyl methacrylate (MMA, third hazard class), which is a product of decomposition of polymethyl methacrylate (PMMA), the thermolysis of the polyester stone gave small amounts of toxic compounds of the second hazard class (diethyl phthalate, styrene) that were used in stone production and molding. The energies of the observed processes were estimated.

Leucosapphire (c-LS) structure and transmission in visible after surface treatment in 90%H2-10%N2 RF discharge are studied. According to AFM, the number of scratches of the mechanically polished surface decreased significantly after removal of about a 300 nm layer (exposure time of 12 h) under unchanged rms of roughness. According to TEM, a two-layer structure formed in the near-surface region consists of an outer 10 nm amorphous layer followed by a crystalline layer of 40-50 nm with a high defect density. The c-LS transmission in the angle of 400-1000 nm either slightly increased or remained unchanged. The demonstrated transmission stability during exposure in 90%H2-10%N2 RF discharge allows us to consider the plasma sputtering as a promising technique for cleaning contaminated windows protecting first mirror of divertor Thomson scattering being developed for ITER divertor Keywords: Leucosapphire, RF discharge, hydrogen, nitrogen, AFM, TEM, surface layer structure, visible transmission.

Migration of plasma erosion products in plasma facilities is studied experimentally and numerically within the framework of modeling transport of plasma-facing materials in the diagnostic ducts of fusion devices. Material transport simulation is discussed for two cases of low and high background neutral gas pressures. Monte Carlo software KITe was used to simulate transport at a neutral gas background pressure 0.1–0.5 Pa—typical during steady-state tokamak operation and during pressure pulses caused by edge localized modes (ELMs). The simulation approach was implemented to describe experiments at the MAGNUM-PSI facility. Fluid dynamic code FLUENT is used to simulate transport during pressure surges as high as 1000 Pa, which can occur in the case of severe disruptions in tokamak plasma discharges, such as vertical displacement events (VDE) or accidental events. The hydrodynamic approach was verified in simulation of target sputtering in the QSPA plasma gun facility.

The adsorption properties of titanium powders with an effective particle size of 18–32 μm mechanoactivated in a planetary ball mill in a protective atmosphere of n-hexane have been studied at different activation times. It has been established that indicators of the specific surface area, Henry’s constant, monolayer capacity, and particle size for activated titanium powders pass through the zones of extreme (min–max) activation values. In this case, the heat of adsorption and the energy of the surface during the adsorption of standard benzene vapor depend on the amount of surface coverage with adsorbed benzene molecules and on the degree of mechanoactivation of the titanium powder. It was found that, at all times of mechanoactivation, the filling of the surface adsorption monolayer has an endothermic sign of the differential molar isosteric heat of adsorption. The reversal of the sign of the heat of adsorption from endothermic to exothermic for all powders corresponds to the completion of the filling of the monolayer and surface nanopores. The observed effect of negativity of the heat of adsorption in the initial region of fillings of the surface of activated titanium powders is explained by the endothermic contribution of the adsorption deformation of the expansion of powder particles with surface nanocracks.

The process of remineralization of hard dental tissues using electrophoresis with a BV preparation that provides the formation of a precipitate of calcium phosphate (brushite) upon the interaction of its components is studied by physicochemical methods including electrochemical impedance spectroscopy and optical and scanning probe microscopy with microanalysis. It is shown in the in vitro experiments that the electrical resistance of a tooth can serve as a criterion of the efficiency of blocking of the dentin canaliculi by the formed precipitate of brushite. The depth of the zone of remineralization is assessed in the case of the treatment with a BV preparation by the method of applications and using electrophoresis. It is found that the latter method possesses a higher efficiency with respect to both the degree of blocking of the canaliculi and depth of penetration into the hard dental tissues. A method of therapy of teeth with the vital pulp is developed based on these studies that shows a high efficiency in the patients from the control group.

Leucosapphire (c-LS) structure and transmission in visible after surface treatment in 90%H2-10%N2 RF discharge are studied. According to AFM, the number of scratches of the mechanically polished surface decreased significantly after removal of about a 300 nm layer (exposure time of 12 h) under unchanged rms of roughness. According to TEM, a two-layer structure formed in the near-surface region consists of an outer 10 nm amorphous layer followed by a crystalline layer of 40–50 nm with a high defect density. The c-LS transmission in the angle of 400–1000 nm either slightly increased or remained unchanged. The demonstrated transmission stability during exposure in 90%H2-10%N2 RF discharge allows us to consider the plasma sputtering as a promising technique for cleaning contaminated windows protecting first mirror of divertor Thomson scattering being developed for ITER divertor.

Studies of contaminants obtained by spraying ITER-grade Be on a quasi-stationary plasma gun facility QSPA-Be are presented. Contaminating films, consisting mainly of Be and O in approximately equal proportions, were deposited on substrates of quartz, sapphire, single crystalline silicon (SC-Si) and NaCl crystal. Characterization of the deposits was performed using SEM, XPS, EBS, AFM, SE, TEM&SAED and micro-interferometry showing polycrystalline BeO films similar as found in JET-ILW. Films on SC-Si and NaCl were used to characterize their composition and morphology. The cleaning rates in the 81.36 MHz RF discharges in He or D2 at 2 Pa were measured on the SC-Si target. The measured etching rate of the deposited films was several times higher than the rate calculated from the theoretical value of beryllium oxide sputtering yield. Test cleaning of these contaminants was carried out in a capacitively coupled RF discharge (CCRF) from the surface of sapphire and quartz plates, which were considered as a mock-ups of the protective window of the first mirror unit (FMU) designed for ITER divertor Thomson scattering diagnostic system (DTS).

The effect of a high-frequency discharge on the change in the topography of the surface of KU-1 optical quartz and transmission of visible light (400–1000 nm) is studied. The working gases of the discharge are D2 and a D2/N2 mixture, in which the fraction of N2 is 25 mol %. The addition of nitrogen increases the rate of sputtering from 60 to 300 nm/h without changing the stoichiometry of the surface layers. After the exposure in plasma, the root-mean-square roughness of the surface decreases from 1.3 to 0.6 nm. The transparence of quartz remains unchanged. The analysis of the roughness and calculation of the diffuse light scattering with a wavelength of 400 nm after passing through quartz are executed using the power spectral density functions.

In plasma devices, in which plasma–wall interaction and material migration are significant, the diagnostic-window transmission may decrease due to the contamination of plasma-cleaning components by sputtered materials. We discuss the cleaning of KU-1 fused silica, which simulates the diagnostic window, from aluminum films in RF plasma generated in pure H2(D2) and Ne and in H2(D2)–0.23Ne mixtures. Aluminum is used as a chemical analogue of Be, which is the main material of the International Thermonuclear Experimental Reactor (ITER) first wall. The morphology of the plasma-treated surface is investigated by atomic force microscopy, the chemical composition is analyzed by X-ray photoelectron spectroscopy, and the transmission spectra in the range 400−1000 nm shows that plasma cleaning is accompanied by the slight reduction of quartz to suboxides and a simultaneous decrease in roughness Rq from 1.3 up to 1.0 nm. After plasma treatment of the quartz surface, a decrease in light transmission by 1.5–2% in the wavelength range 400–750 nm is observed. Further sputtering of the purified quartz surface with the removal of a layer with a thickness of more than 300 nm is accompanied by gradual smoothing of the surface and a decrease in Rq to 1 nm, but with the retention of reduced light transmission. All investigated gases, hydrogen isotopes, neon and D2(H2)–Ne mixtures, are suitable for removing Al films from the quartz surface at a RF power of several W/cm2 and temperatures of 20–100°C.

The effect of a cleaning discharge plasma on the KU-1 optical quartz surface topography and transmission in visible and near IR ranges (400-1000 nm) was studied. For the study, we used crossed DC and RF discharges in D2 and D2/N2 mixture, where the N2 fraction was ~25 mol %. The addition of nitrogen increased sputtering rate from 250 to 1200 nm / h while maintaining stoichiometry of the surface layers. The rms surface roughness decreased after the plasma exposure from 1.3 to 0.6 nm, while the quartz transmittance has not changed. The surface roughness analysis and calculation of diffusion scattered light at 400 nm transmitted through the quartz were performed using the power spectral density function of AFM.

The intensity of light emitted by plasma and passing through diagnostic quartz windows in tokamaks and other fusion power devices may decrease due to first-wall materials (Be in the International Thermonuclear Experimental Reactor (ITER)) sputtered and re-deposited onto the window surface facing the plasma. In the experiments, aluminum films (analog of Be) are removed from the surface of fused silica KU-1 in plasma of a RF discharge in a H2–N2 mixture prototyping one of the in-situ cleaning techniques. The admixture of nitrogen to hydrogen plasma increases the sputtering rate of aluminum films. Using X-ray photoelectron spectroscopy (XPS) and atomic-force microscopy (AFM), we demonstrate that cleaning is accompanied by the weak reduction of quartz, nitriding with the addition of nitrogen, and the formation of a “honeycomb” structure with increased roughness. These processes are more pronounced with the repeated deposition of Al and subsequent cleaning. Light transmittance in the range 400–1000 nm does not change within 1% in the case of a partial change in the stoichiometry of the surface layers and an increase in the roughness from 1.3 to 4.5 nm. Numerical estimates of the forward and backscattering of light by a rough quartz surface show that the reduction in transmission due to scattering does not exceed a few tenths of a percent, which is in agreement with the measurement data. Thus, the demonstrated stability of the quartz transmittance during the deposition of aluminum and subsequent long exposure in the plasma of a RF discharge makes it possible to consider the cleaning technique under consideration promising for use in ITER.

The effect of cleaning with D2–(2–4) mol % N2 glow discharge plasma on the reflectivity of Mo(111) single-crystal mirrors is studied. The surface of each mirror is prepared by mechanical polishing with diamond pastes or diamond powder. Polishing of the mirrors is accompanied by the formation of a layer of material up to 3 microns thick, different in structure from the bulk metal. The peculiarity of this layer is a gradual improvement in its structure further away from the surface of the mirror and transition from an amorphous layer to a layer with nanoscale crystallites, and then a gradual transformation into the structure of an unbroken single crystal. When polishing, the diamond abrasive is pressed into the surface layer of the mirror. During the plasma-cleaning process, carbon particles pressed into the surface layer of the mirror initiate the development of negative roughness (pits or depressions). At the same time, a 5–10-nm layer of molybdenum nitride is formed. In disordered layers of the mirrors, the probability of the origination and growth of blisters is reduced. Aluminum is chosen as the metal that changes the total reflection coefficient of Mo. The use of a D2–N2 mixture to increase the rate of Al sputtering in the last stage of cleaning is replaced by plasma exposure in deuterium with $${\text{D}}_{3}^{ + }$$ ions, which initiates the dissociation of molybdenum nitride and the removal of nitrogen from the surface layer of the mirror. As a result of prolonged plasma exposure, the reflectivity of the mirrors polished with diamond paste increases to a steady-state value close to the reflection of the reference mirror.

Scientific and technological program of ITER requires measurement of plasma parameters using variety of diagnostics, ~ 20 of which are the optical ones [1]. The plasma emitted light and/or laser beams will travel by in-vessel optical labyrinths between torus and analyzing equipment. The closest to plasma optical elements, so-called first mirrors (FMs) and windows (FWs), will operate in harsh environmental conditions such as high temperature, particle fluxes and deposition of eroded first wall materials (Be, W etc.) [3]. During periods of Mirror Conditioning States (MCS), the optical performance of FMs and FWs has to be restored by an appropriate cleaning system. The system based on the radio frequency capacitively coupled (RFCC) discharge with a mirror or window used as a RF electrode is currently considered as the main approach [4]. However, most research of the plasma cleaning were performed using Be proxy materials (Al, Au etc.) due to its high toxicity. The study of sputtering Be deposits are of high importance to prove the plasma cleaning efficiency. The report presents results of pilot experiments on deposition and in-situ sputtering of Be deposits in the QSPA-Be facility located in Bochvar institute. QSPA-Be facility was designed to simulate plasma heat loads related to ITER ELMs / disruptions [5]. The pure Be target evaporation by one pulse of QSPA-Be provided deposition of ~7 nm contaminant layer with ~70% of beryllium. The beryllium films were characterized using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The in-situ plasma cleaning was realized by exposing in 81 MHz helium discharge at pressure of 2 Pa. The cleaning process was controlled observing beryllium emission line in plasma column spectrum. The FW mock-up characterization was performed after 2 hours of the plasma exposure. Cyclic removal of Be-depositions in QSPA facility is planned to be done in 2020.

The effect of D2–N2 glow discharge plasma on the reflectivity of single-crystal Mo(111) mirrors is studied. The surface of each mirror is processed by mechanical polishing with diamond pastes to a roughness of hq = 5 nm. During polishing, abrasive particles are embedded in the surface layer of the mirror. Exposure to an ion fluence of 1.4 × 1024 m–2 leads to an increase in hq = 7 nm. After irradiation and the removal of a 30 nm-thick Mo layer the total reflection coefficient Rt in a 400–1000 nm region increases by 5–10% to a steady-state value (56–58)%. The increase in Rt may be caused by the preferential removal of carbon during the ion-sputtering process.

A new IR-spectroscopy (infrared) technique allowing investigation of the transformation of gaseous WF6 on a W surface heated up to 860 K in a hydrogen and argon atmosphere is proposed. The weak chemical adsorption of WF6 on W substrates is observed. The intermediate reaction products of WF6 with solid W above 670 K are penta- and tetra-tungsten fluorides. The presence of other low-valent tungsten fluorides is possible in the form of adsorbed oligomeric molecules (dimers or trimers). It is shown that low-valent tungsten fluorides are strongly adsorbed on the surface of W. The adsorbed layers formed on the W substrate in the WF6 + H2 mixture and pure WF6 str identical in composition.