Transformations of hydrocarbon radicals moving along a stainless steel tube

Transport of exhausted thermonuclear fuel in the ITER divertor and pumping duct was modeled on a specially designed dc glow discharge setup using mass spectrometry, optical and electron microscopy, and electron probe microanalysis. Transport and deposition of hydrocarbon radicals transferred in an H₂/C _x H _yx mixture through a hollow stainless steel anode at a total mixture pressure of 8–212 Pa and a methane content to 15 mol % were considered. It was shown that deposition of radicals and ions (CH₃, C₂H₃, C₂H₅) with kinetic energies of 0.03–3 eV on the anode inner surface at 600 K was suppressed to a large extent. In the temperature range of 600–800 K, deposition of ions and radicals with kinetic energy of ~3 eV was partially restored with the formation of soft a-C:H films, while thermalized radicals were not condensed.     

Structural-phase transformations at annealing of highly reflective mirrors based on aluminum and silver

Multilayered prototypes of Al and Ag total reflection mirrors with a protective coating of amorphous ZrO₂ oxide were analyzed using transmission electron (cross-sectional method), optical, and scanning (with electron probe microanalysis) microscopes. The prototypes’ reflectivity was measured by the recording of reflection spectra in the wavelength range 200–1100 nm. The structure of the mirrors was studied by X-ray diffraction reflection. High temperature annealing (8 h) did not change the stoichiometric composition of the protective coating. The reflectivity of the Al mirrors in the wavelength range 700–1100 nm and the Ag mirrors in the wavelength range of 500–1100 nm remained unchanged in spite of recrystallization of the polycrystalline metal films and the incipient process of amorphous ZrO₂ crystallization. The mass of the crystalline oxide after annealing was several percent of the total amorphous oxide mass. At the same time annealing led to the occurrence of local voids on the aluminum/upper oxide interface. Such defects were not observed on the Ag mirrors. As a whole, the Ag mirrors turned out to be more stable to heating as compared to those made of Al.     

Effect of nitrogen and ammonia on transfer and deposition of hydrocarbon radicals in different regions of hollow-cathode glow discharge

The effect of addition of nitrogen or ammonia in an amount equal to the flow of methane entering as a 7: 1 H₂/CH₄ mixture into a hollow-cathode dc glow flow discharge on the rate of deposition/erosion of amorphous hydrocarbon (a-C:H) films at 300 K has been studied. The introduction N₂ or NH₃ into the mixture facilitates the transition from deposition to erosion of a-C(N):H films in the hollow cathode, but has a little effect on the growth rate of a-C(N):H films in the positive column and in the afterglow of the discharge. It has been suggested that the changes in the a-C:H film deposition/erosion rate are due to the formation of hydrogen cyanide, mainly, on the hollow-cathode surface.     

The hydrogenation of methyl on metallic surfaces

The stream technique was used to comparatively analyze the characteristics of the deposition of a-C:H films from methyl radicals transferred by a carrier gas CH₄/C₂H _y /H₂ (y = 2, 4, 6) in a quartz tube with cylindrical insets made of Cu, Ni, Fe, W, Si, and stainless steel (SS), initial and coated with thin Pd or Rh films, over the temperature range 300–1000 K. The deposition of methyl was fully suppressed in a tube section heated to 380–800 K with all the insets specified. During further mixture movement outside this section in the tube with a decreasing wall temperature, carbon deposition resumed. The most effective catalyst of the hydrogenation reaction was stainless steel. Radicals and unsaturated hydrocarbons capable of polymerization at 300–400 K were fully removed from the carrier gas flow (CH₄/C₂H _y /H₂) after several hundreds of collisions with the surface of SS heated to 420–470 K. The possibility of creating an SS recombination filter for hydrocarbon radicals (the performance of radical hydrogenation reactions) transferred by a CH₄/C₂H _y /H₂ laminar flow was demonstrated. The deposition of a thin Pd film (∼10 nm) on steel did not increase the effectiveness of the surface with respect to radical recombination reactions. At the same time, Rh films increased the catalytic effectiveness of the surface of SS with respect to the hydrogenation of methyl and unsaturated hydrocarbons (380–420 K). The data obtained were used to select temperature conditions and mutual arrangement for the construction elements of an ITER diverter made of tungsten and stainless steel.     

The Topography of Surface and Light Transmission by Quartz Windows after Exposure in a High-Frequency Discharge in Deuterium and Mixture of Deuterium with Nitrogen

Technical Physics - 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....     

WO3 oxide film formation on tungsten in O2/H2 discharges

The features of tungsten oxidation in a flowing O₂ or O₂/H₂ mixture glow discharge with a hollow cathode are investigated in the cathode, plasma, and afterglow regions at T = 300–350 K. The structure and composition of the samples are analyzed via reflection high-energy electron diffraction, reflection X-ray diffraction, electron probe microanalysis, and X-ray photoelectron spectroscopy. The results of analysis show that the metal surface is covered by a thin film (5–10 nm thick) of amorphous porous hydrated tungsten oxide (WO₃) after its exposure to the discharge and storage in air. The study of the film composition using a time-of-flight mass spectrometer indicates that the WO₃ film contains (WO₃) _n (n = 1–6) clusters and water molecules adsorbed in the pores. After exposure of the polycrystals to the O₂/H₂ discharge, the selective intense oxidation of individual grains is detected in the cathode region; the surrounding areas are subjected to weaker oxidation. The thicknesses of the WO₃ films on neighbouring grains differ by more than tenfold. Such grains can be the source of tungsten dust in plasma installations.     

Blistering of mechanically polished molybdenum upon its exposure to deuterium-containing plasma

Recent data on the blistering process in polished polycrystalline Mo for the case of direct-current glow discharge in deuterium and D₂/2–4 mol % O₂ or N₂ admixtures, at an energy of incident molecular ions of 70–120 eV and a pressure of 14 Pa, are reported. Depending on the method of metal surface polishing, the initial metal grains are broken up into mutually disordered regions of smaller sizes (subgrains); the chemical composition of the damaged layer changes. In the formed structure, blistering can develop easily or be impeded. Small additions of O₂ or N₂ to deuterium facilitate the blistering.     

Formation of Films of Tungsten and its Oxides in a High-Frequency Capacitive Discharge in a D<Subscript>2</Subscript>-O<Subscript>2</Subscript> Mixture

A technique for tungsten-film deposition on different substrates in asymmetrical high-frequency (1.76 MHz) capacitive discharge in a D₂?6.5 mol % O₂ mixture under a total pressure of 15 Pa and at 60–130°C is considered. A circular W strip near the upper inner edge of a cylindrical hollow cathode with a radius of 4.2 cm and a height of 10 cm is the source of W particles. The smooth transition from sputtering of the inner surface to deposition occurs at a distance of about 4 cm from the upper boundary of the open part of the cathode. W, Mo, ZrO₂, Si, and Cu substrates are placed in the lower closed end (bottom) and on the inner lateral cathode surface. At the upper cathode edge the sputtering yield is (4–5) × 10^?2 at/ion. The mass rate of W deposition on the cathode bottom does not depend on the substrate type and is 40 μg/(cm² h). The peculiarities of the composition, morphology, and structure of W films obtained on the lateral surface and bottom of the hollow cathode are discussed.