Gennadiy Efimovich Remnev

The formation of plasma on the surface of BaTiO ₃ ferroelectric ceramics in an argon atmosphere in the pressure range 1 × 10 ^–5 –1 × 10 ^–2 Torr has been experimentally studied. Based on the discharge voltage and current, the energy supplied by the driving pulse generator for plasma formation was investigated. It is shown that at argon pressures ≥10 ^–3 Torr, the fraction of energy spent on plasma formation increases significantly due to the growth of the discharge current. The elemental composition of the plasma was examined by optical emission spectroscopy, and the electron temperature and density were determined from analysis of Ar II ion spectral lines, taking into account the optical thin condition of the plasma and the McWhirter criterion. Local thermodynamic equilibrium in the plasma is achieved at argon pressures ≥10 ^–3 Torr. The dependence of the electron temperature and density on argon pressure has been determined. As the argon pressure increases, the electron temperature rises from 0.8 to 1.2 eV, while the electron density reaches (2‒5) × 10 ¹⁵ cm ^–3 . The concentration ratio of argon ions Ar II to Ba II and Ti II ions in the plasma has been determined over the studied pressure range.

The article discusses the design features of a three-electrode spark gap with field distortion based on the results of an iterative calculation of the configuration and the results of a study of its time characteristics in comparison with a two-electrode spark gap and a three-electrode spark gap without calculating and equalizing the electric field in the spark gap. The design of the gap provides alternating breakdown of gaps under conditions of overvoltage and a sharp inhomogeneous electric field strength determined by the special shape of the electrodes. The spark gap is part of an experimental stand under development for the generation of neutron beams by powerful pulsed accelerators of charged particles. Taking into account the continuous operation of the accelerator about 106 repetitions, the problem of ensuring the required erosion resistance of the commutator electrodes and the stability of discharge formation without deterioration of switching characteristics is acute. Despite many years of research, no universal solution to these problems has been found. Based on the above, it became necessary to carry out this work related to the development of such gaps. The switching voltage was in the range of 147.5 - 304.5 kV with a maximum switching current of up to 87 kA. It is shown that the introduction of a distorting electrode into the spark gap during the configuration of the electric field reduces the breakdown voltage slightly (7.3-12.8%). The jitter of the response time relative to the start time of the charging pulse has been determined. The spark gap ensured the formation of a branched structure of the spark channel, which reduced electrode erosion, switching time, and voltage drop across the spark gap.

The experimental studies of a surface discharge on the ferroelectric ceramics in an argon atmosphere are presented. The plasma source is based on BaTiO₃ ceramics and designed in a cylindrical shape. The influence of gas pressure in the range of 10^–5–10^–2 Torr on the emission spectrum of plasma and surface discharge characteristics are established. The plasma emission spectrum was received using the optical emission spectroscopy. The spectrum lines corresponded to atoms and ions of elements related to the ferroelectric (Ba, Ti, O) and residual atmosphere (Ar). The discharge characteristics were investigated by analyzing the voltage and discharge current signals.

The collective acceleration of helium ions from its residual atmosphere in the Luce diode was studied at helium pressures from 0.13 to 0.23 Pa. The energy of accelerated ions was determined from the drift velocity of the virtual cathode accelerating the ions. The number of ⁴He was determined by radioactivities of ¹³N and ³⁰P induced in h-BN and Al targets via the nuclear reactions ¹⁰B(α,n)¹³N and ²⁷Al(α,n)³⁰P. The efficiency of capturing ⁴He ions in collective acceleration from the residual helium atmosphere was estimated as 0.25%. With increasing helium pressure above 0.15 Pa, the energy of the main ion group noticeably decreased to 0.46 MeV/amu compared to the acceleration from a usual residual atmosphere (~0.6 MeV/amu); however, the probability of ion acceleration to a specific energy of up to 1.57 MeV/amu increased significantly. Such increases in the ion energy were accompanied by the appearance of the signal of the second virtual cathode 7–9 ns after the appearance of the first virtual cathode.

The unique flash heating characteristics of intense pulsed ion beams (IPIB) offer potential advantages to fabricate high-performance coatings with non-equilibrium structures. In this study, titanium-chromium (Ti-Cr) alloy coatings are prepared through magnetron sputtering and successive IPIB irradiation, and the feasibility of IPIB melt mixing (IPIBMM) for a film-substrate system is verified via finite elements analysis. The experimental results reveal that the melting depth is 1.15 μm under IPIB irradiation, which is in close agreement with the calculation value (1.18 μm). The film and substrate form a Ti-Cr alloy coating by IPIBMM. The coating has a continuous gradient composition distribution, metallurgically bonding on the Ti substrate via IPIBMM. Increasing the IPIB pulse number leads to more complete element mixing and the elimination of surface cracks and craters. Additionally, the IPIB irradiation induces the formation of supersaturated solid solutions, lattice transition, and preferred orientation change, contributing to an increase in hardness and a decrease in elastic modulus with continuous irradiation. Notably, the coating treated with 20 pulses demonstrates a remarkable hardness (4.8 GPa), more than twice that of pure Ti, and a lower elastic modulus (100.3 GPa), 20% less than that of pure Ti. The analysis of the load-displacement curves and H-E ratios indicates that the Ti-Cr alloy coated samples exhibit better plasticity and wear resistance compared to pure Ti. Specifically, the coating formed after 20 pulses exhibits exceptional wear resistance, as demonstrated by its H³/E² value being 14 times higher than that of pure Ti. This development provides an efficient and eco-friendly method for designing robust-adhesion coatings with specific structures, which can be extended to various bi- or multi-element material systems.

Intense pulsed ion beam (IPIB), featured with pulsed high-power density, has been widely used in the modification of materials. The influence of IPIB irradiation on surface microstructure and phase structure of (TiZrNbTaCr)C ceramics was investigated in this work. Experiments were carried out using TEMP-4M accelerator with peak accelerating voltage, current density, and pulse duration (FWHM) of 220 kV, 150 A/cm2, and 80 ns respectively. Atomic force microscope (AFM), scanning electron microscope and Energy-dispersive X-ray spectroscopy (SEM-EDS), as well as X-ray diffraction (XRD) were used to analyze the surface microstructure and phase structure of (TiZrNbTaCr)C ceramics under IPIB irradiation. The AFM and SEM images showed that the grain size of (TiZrNbTaCr)C increased, and the size and quantity of holes decreased after IPIB irradiation which might improve the erosion resistance of material. After IPIB irradiation, the segregation of Cr and Ta elements were observed by EDS measurement. The phase structure stability of samples under IPIB irradiation was confirmed by XRD and the lattice parameters and crystal spacing was discussed as well.

Application of powerful submicrosecond ion beams for the synthesis and modification of material properties is reviewed. Powerful ion beams originally developed for inertial thermonuclear fusion have been increasingly widely used over last 30 years as a high-power pulsed heating source that provides ample opportunities for modifying the surface layer of materials. By varying key parameters of the beams, such as the co-mposition (type of ions), the accelerating pulse duration of (10 ns–1 μs), the kinetic energy of ions (0.1–1 MeV), the energy density inputted by the beam to the target surface per pulse (0.1–50 J/cm²), the main areas of application of intense ion beams in materials science have been determined: modification of the surface layer by ultrafast quenching, melting and ultrafast recrystallization with the formation of micro- and nanostructures, pulsed implantation of ions accompanied by exposure to energy factors, deposition of thin films, and synthesis of nanosized powders from ablative plasma.

X-ray sources based on pulsed electron accelerators stimulate the development of bremsstrahlung converter designs. The numerical optimization of transmission-type X-ray targets for maximum X-ray output by pulsed electron beams was carried out in the present work. The targets featured a combination of a heavy element (tungsten or molybdenum) X-ray conversion layer and a titanium membrane that served as the vacuum window, thermal shielding for converter heat, and an electron dump. The energy spectrum of the electron beam generated via explosive emission was analyzed via the space-charge effect, and was utilized for the source sampling algorithm for electron transportation simulation with a Monte Carlo method for X-ray emission analysis. It was revealed that the transmission photon intensity of a mono-material target is primarily affected by the thickness of the target, and there exists an optimal target thickness within which the photon fluence is restricted by insufficient electron stopping; when exceeded, the extra thickness of the X-ray converter target imposes absorption and attenuates the generated X-ray. Analysis on dual-layer targets proved that this optimized converter target thickness, combined with a proper titanium window, produces the highest X-ray photon emissions.