Персона: Писарев, Александр Александрович
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ALUMINIUM OXIDATION IN PLASMA OF ABNORMAL GLOW DISCHARGE
Aluminum oxide layers in all its various forms have become widespread due to the unique combination of properties that can be modified by varying the conditions of their growth. The alumina layer can either be applied to the substrate by chemical and physical methods or grown by oxidation. For practical purposes, layers of various thicknesses and structures are needed. The standard method for obtaining thick (of the order of 100-1000 nm) porous layer is electric arc anodization in weak electrolytes. The standard method for obtaining thin (about 10 nm) layers is thermal oxidation. Dense layers of intermediate thickness are difficult to obtain by such methods. There are few papers in the literature that investigate the possibility of obtaining oxide layers with a thickness of tens of nanometers by oxidizing aluminum in oxygen plasma [1-5]. The description of the kinetics of the oxidation process in those works was given on the basis of the assumption of the diffusion character of oxygen transfer from the surface into the interior of the metal. This approach is absolutely unsuitable for description the transport of oxygen and aluminum through the oxide layer, since both oxygen and aluminum in the oxide are in the form of ions, and an electric charge is formed on the surface of the dielectric facing the plasma, so that the transport of oxygen coming from the plasma must occur under by the action of an electric field in the oxide dielectric layer. In this work, experiments on plasma enhanced oxidation (PEO) were carried out on the oxidation of aluminum in the anomalous glow discharge oxygen plasma, which provides uniform treatment over the entire surface of samples of arbitrary shape. Also, a simple model was proposed for description of the oxidation kinetics, taking into account oxygen transport in the electric field.
HELIUM THERMAL DESORPTION FROM TUNGSTEN AFTER ION BEAM IRRADIATION AT ELEVATED TEMPERATURES
Helium (He) is a product of deuterium-tritium reaction, so appearance of helium impurities will be unavoidable. In addition to He implantation from fusion plasma, He can be introduced into material by both neutron irradiation and tritium radioactive decay. Presence of He in plasma-facing materials may significantly influence their mechanical properties and surface morphology [1, 2], as well as hydrogen isotope recycling [3, 4]. Tungsten (W) will be used as a plasma-facing material in ITER divertor [5], and it is considered also for application in future fusion devices. Therefore, investigation of He interaction with W is of great interest.
HYDROGEN AND HELIUM RETENTION IN TUNGSTEN UNDER ION IRRADIATION
Interaction of helium and hydrogen ions with tungsten is intensively investigated during last decades in relation to construction of fusion reactor. Tungsten has the high melting temperature and the energy threshold for sputtering and, therefore, is considered as plasma facing material (PFM) in fusion devices in the area of largest heat loads and small energies of ions (divertor area). In particular, tungsten will be used in the international experimental reactor ITER, which is now under construction.
ТЕРМОДЕСОРБЦИЯ ДЕЙТЕРИЯ ИЗ РАДИАЦИОННЫХ ДЕФЕКТОВ В ВОЛЬФРАМЕ
Detrapping of deuterium ions from point defects created by pre-irradiation in polycrystalline tungsten has been studied by thermal desorption spectroscopy. Different fluences and ion energies were used to investigate various types of defects. The heating rate β was also varied in different experiments in the range of 0.15-4 K/s to determine detrapping energies from the shift of peak positions.
ВЛИЯНИЕ УЛЬТРАФИОЛЕТОВОГО ИЗЛУЧЕНИЯ НА СОДЕРЖАНИЕ И ДЕСОРБЦИЮ ДЕЙТЕРИЯ ИЗ СООСАЖДЕННЫХ ЛИТИЕВЫХ СЛОЕВ
The influence of ultraviolet irradiation of co-deposited lithium layers on the content and desorption of deuterium from them is considered. It was found that exposure to ultraviolet radiation suppresses desorption at high temperatures, facilitates desorption at low temperatures. Effects are considered that can form the basis for the development of methods for determining the places of accumulation of lithium hydride in tokamaks with lithium walls, as well as facilitating the removal of heavy hydrogen isotopes from the walls of installations.
HYDROGEN CO-DEPOSITION WITH METALS IN PLASMA DISCHARGE
Deposition of a single element film is always accompanied by co-deposition of a certain amount of other elements. This can be done properly to improve properties of the coating or due to contamination by impurities. In the field of thermonuclear fusion research, where hydrogen isotopes are used as a fuel, co-deposition with sputtered material from the wall is one of major mechanisms of hydrogen isotopes accumulation in the installation. Since D-T fuel will be used in ITER and future fusion reactors, accumulation of radioactive tritium will limit the lifespan of the installations due to safety concerns. For example, tritium accumulation in ITER is limited by 1 kg. This is why carbon materials were not accepted for the use in ITER. Basing on experiments, it was predicted that the safety limit could be reached after 100 of shots with tritium. Recent experiments in JET [1] demonstrated in the case of “ITER-like” wall (first wall – Be, divertor area - tungsten) accumulation of deuterium fuel in the co-deposits was 20 times lower than in the full-carbon wall campaign. This is both due to smaller amount of co-deposits and smaller concentration of deuterium in them.
PULSED ABNORMAL GLOW DISCHARGE WITH HOLLOW CATHODE FOR NITRIDING OF INTERNAL CYLINDRICAL SURFACES
Plasma nitriding is a method of thermochemical treatment, which is widely used to enhance surface hardness, fatigue strength, and corrosion resistance of steels [1,2]. In industry, glow discharge is commonly used for this purpose. A specific task of plasma technologies is treating of cavities, which are usually inaccessible for plasma. Still, the need to modify cavities and tubes of small diameters and large aspect ratios exists. Abnormal glow discharge with hollow cathode in the pulse-periodic mode was proposed for this purpose in [3]. This work is devoted to investigation of ignition and properties of the abnormal glow discharge in tubes and demonstration of nitriding of internal surfaces of the tubes.
Deuterium trapping in co-deposited layers of ITER-relevant materials
Hydrogen isotope accumulation in fusion devices is a serious problem. Because deuterium-tritium mixture will be a working gas in future fusion devices, including ITER tokamak, tritium accumulation is an issue from the perspective of radiation safety. In total, only 700 grams of tritium are allowed to be present in ITER vessel at any time, with additional 120 in the cryopumps, and 180 grams allocated to measurement error, to the total of 1000 grams.
DEUTERIUM RE-EMISSION AND THERMAL DESORPTION FROM IRON AND EUROFER
Reduced-activation ferritic-marthensitic (RAFM) steels, such as Eurofer, are considered as candidates for structural materials in fusion reactors due to the high thermal conductivity, the low thermal expansion coefficient and good resistance to radiation swelling. There are also some concepts of fusion reactors, where RAFM steels also considered as material for plasma-facing components. In this regard, the key aspects of hydrogen (H) isotopes interaction with RAFM steels, such as tritium (T) retention and migration in these materials are particularly important as a point of safety concern.
TECHNOLOGICAL APPLICATIONS OF PLASMA SURFACE INTERACTIONS
Plasma is the forth state of matter, which is characterized by a high intrinsic temperature. Interaction of this substance with matter leads to serious consequences both for the matter and the plasma. Many effects of plasma-surface interactions are used for practical purposes, and this brief review gives some examples. We will concentrate on applications of low temperature plasma, which is characterized by the electron temperature below 105 K.