Bulletin of the Russian Academy of Sciences: Physics最新文献

We have studied experimentally the shape evolution of the interacting initial head-to-head (h2h) and tail-to-tail (t2t) charged domain walls (CDW) and growing isolated domain in the Y-cut LiNbO₃ plates. The wedge-like domains were created and grew by electric field application using biased tip of scanning probe microscope. Two h2h and one t2t initial CDWs have been produced during phase transition in the crystal with composition gradients created by in-diffusion and out-diffusion of Li. The formation and growth of cogged CDW has been revealed for domain interaction with t2t CDW in contrast to h2h CDW. Near the t2t CDW domain elongation is slowed down, while the widening of the domain part with neutral walls continues. The growth anisotropy leads to formation of the region with increased local tilt and formation of cogged CDW by generation of additional spikes. The obtained effects were considered in terms of kinetic approach to domain wall motion considering abnormal local field distribution in the vicinity of initial CDW with effectively screened depolarization field. The discovered effect can be considered for domain wall engineering thus paving the way for manufacturing of the nanoelectronics devices based on the CDWs.

The influence of conductive coating materials on the magnitude of short-circuit currents (SCC) in single-domain and polydomain Z-cut polar lithium niobate (LiNbO₃) crystals is investigated. The domain structure of the samples was determined by piezoresponse force microscopy (PFM) using a probe microscope. Indium and silver symmetrical (identical) coatings were used for the study. Temperature dependences of SCC were measured using a hardware complex with special software in the temperature range from room to 350°C at a rate of 2 deg/min in air without applying an external electric field. Even at room temperature the SCC are observed on all investigated samples. The direction of the SCC flow depends on the conductive coating material, and the domain structure influences the current magnitude during heating. The current flow was in the positive direction for In conductive coatings and in the negative direction for Ag conductive coatings. In the single-domain samples observed higher currents than those in polydomain ones. The surface of the conductive coatings before and after heating was investigated using an optical microscope. Significant changes in the structure and color of the conductive coatings are observed. The obtained data demonstrate a significant dependence of SCC on the type of domain structure and the material of conductive coatings, which is important to consider when developing stable piezoelectric devices operating in a wide temperature range.

Influence of density dependent hyperon–nucleon forces on characteristics of neutron stars is investigated. In particular, the role of the exponent γ, determining the dependence of interaction on the nucleon density, in the description of the matter of neutron stars is studied. It is also shown that the hyperon–nucleon forces proportional to the nucleon density and three-body hyperon–nucleon–nucleon forces can lead to qualitatively different results in neutron stars.

We provided an overview of the reports presented at the 75th International Conference “Nucleus-2025: Nuclear Physics, Elementary Particle Physics, and Nuclear Technologies,” which took place in St. Petersburg from July 1 to 6, 2025. The program covered nuclear structure, nuclear reactions, astrophysics, neutrino, high energy and particle physics, nuclear technologies. Emphasis was placed on medical, energy, radioecology and materials applications, demonstrating the growing interdisciplinary impact of nuclear science.

The influence of a uniform axial magnetic field on the drift of charged particles from the apex of a conical cathode in the surrounding gas is studied. A self-consistent analytical model is developed to describe this influence within the space-charge-limited current regime. Assuming the shape of the drift region to be conical, it is possible to determine the dependence of its opening angle on the electrode angle, the magnitude of the applied magnetic field, and the mobility of charge carriers.

The glow accompanying a self-sustained subnanosecond discharge in nitrogen in the pressure range from 4 to 15 atm was recorded using the streak method. Breakdown delay time and pulse breakdown voltage of the discharge gap were recorded oscillographically. The experiments were carried out in uniform and non-uniform average electric fields. In these cases, the macro geometry of the discharge gap did not provide an increase in the electric field to the value necessary for the implementation of the electron runaway mode according to the classical runaway criterion. It is shown that at the initial stage of development, the discharge has a volumetric shape, which later turns into a spark. The discharge contraction, as a rule, begins from the cathode and the anode almost simultaneously. The conducted modeling of the dynamics of ionization processes showed that at the stage of the volumetric column formation, a short-term increase in the electric field near the anode occurs. As a result, the ionization of gas in the anode region increases sharply, which initiates the development of a spark channel, including from the anode.

Numerical simulation of the shock wave propagation in the discharge chamber with the high-current discharge in high density hydrogen at initial pressure of 0.1–32 MPa under non-stationary energy release at current rise of rate of 10 GA/s was carried out by the finite-differences method. The source of the disturbance (shock wave) was a forming discharge channel in the interelectrode gap along the axis of the cylindrical chamber. The power disturbance of the source was given by the experimental power value in near-axis area.

The processes on the cathode surface prior to the establishment of a diffuse mode of vacuum arc discharge on gadolinium cathode was investigated. Using high-speed video recordings and voltage waveforms, the breakdown process and the ejection of cathode material droplets were examined. The temporal dependences of cathode temperature and discharge voltage after breakdown were analyzed. Characteristic times for the transition to the steady-state diffuse discharge mode were determined. It was found that during breakdown and after, when discharge is unstable, droplets and voltage spikes can occur. Discharge stabilization can be achieved by increasing the cathode temperature, which leads to the transition to a mode with a voltage of about 5 V and the absence of voltage spikes and droplets. These results are significant for the development of a plasma source for the plasma separation of spent nuclear fuel.

Numerical kinetic modeling of spherically expanding plasma with parameters characteristic of the plasma of the cathode spot of a low-current vacuum arc is performed. It is shown that under such conditions a group of electrons arises in the plasma, the energy of which practically does not change during expansion. As a result, at some distance from the cathode, the electron velocity distribution function in the direction of plasma expansion differs significantly from the drifted Maxwell distribution by the presence of a group of suprathermal electrons. The distribution function for velocities perpendicular to the direction of expansion remains Maxwellian.

Accelerators that can be used for small Cubesat-class spacecraft are currently gaining popularity. One of these accelerator types is an ablative pulsed plasma accelerator, which allows spacecraft to rotate at small angles, adjust the orbit, etc. The paper presents spectral characteristics studies of plasma radiation produced by ablative pulsed plasma discharge in vacuum. A coaxial ablative pulsed plasma source is a system of coaxial electrodes with POM-C dielectric located between them. Operation is based on a high-current pulsed discharge, energy invested in the discharge (5.6 J) is spent on dielectric ablation, dielectric mass ionization, acceleration and radiation. Radiation was recorded in the frontal and lateral directions through a quartz window using Solar S100 (200–1100 nm, resolution δ ~ 1 nm) spectrometer. During spectral analysis, emitting substances were identified, including atoms, ions and molecules, evaporating from the dielectric surface (C, O, H), electrodes (Cu) or being in the residual atmosphere (N), discharge dynamics were studied using a G5-54 pulse generator.