Physics of Atomic Nuclei最新文献

The problem of high heat fluxes on tokamak reactor divertor targets, which hinder the development of durable divertor targets with extended operational lifetimes, is considered. Potential approaches to enhance the allowable heat flux on the high-heat-flux components of the divertor are outlined. In order to verify the operability of one of the approaches, thermal cycling tests of the mockup were performed at the Tsefey-M facility. Thermal analyses carried out prior to the thermal cycling tests, as well as the experimental results themselves, are presented to enable a qualitative comparison. The method under study demonstrated its effectiveness, potentially enabling an increase in the permissible heat flux on the divertor up to 30 MW/m² or more.

Classic methods for plasma current measurement in tokamaks based on Faraday’s law of induction (Rogowski coil) or the Hall effect (Hall sensor) have a number of disadvantages that can be most acute in fusion reactor steady-state operating regimes (strong stray fields, operation in a long pulse with a constant plasma current). To ensure reliability of the measurements, the use of current sensors based on other physical principles may be required. Such a sensor is a fiber-optic current sensor (FOCS) based on the magneto-optic effect (Faraday effect). An analysis of international experience in FOCS application for plasma current measurements (JET, EAST, Tore-Supra tokamaks, etc.) was carried out in this work. Based on analysis, the concept of an improved FOCS measurement scheme for the T-15MD tokamak was proposed. The proposed FOCS reflective (double-pass) circuit, operating on the interferometer principle with probing at an intermediate frequency, will make it possible to carry out measurements over the entire designed range of plasma currents (up to 2 MA) with an error of 0.5 kA and a time resolution of 100 μs.

Comparative studies of tungsten surface damageability under irradiation with steady-state helium ion fluxes and pulsed helium ion and helium plasma fluxes in the ion-beam accelerator (ILU) and in the Vikhr Plasma Focus (PF) installation have been carried out. The parameters of irradiation with steady-state He⁺ ion fluxes in the ILU: helium ion energy of 30 keV; fluences of 1.0 × 10¹⁸ and 2.0 × 10¹⁸ cm^–2; and target temperature during irradiation not exceeding ~500 K. For irradiation with pulsed fluxes of helium ions and helium plasma in the Vikhr PF installation, the samples were placed in the cathode zone of the Vikhr PF chamber at a distance of 2, 4, and 6 cm from the anode. Parameters of irradiation of samples in the Vikhr PF: duration of ion and plasma exposure of 10–30 and 50–200 ns, respectively; power density of plasma in the range of ∼10⁷–10⁹ W/cm² and ions in the range of ~10⁹–10¹⁰ W/cm²; number of pulses N = 5, 15, and 30; helium ion energy of ~100 keV; and plasma temperature of ~1 keV. Under irradiation with steady-state He⁺ ion fluxes with a fluence of 10¹⁸ cm^–2, formation of blisters with peripheral rupture of caps characteristic of brittle materials is observed. An increase in the irradiation fluence by a factor of two leads to a change in the mechanism of surface failure; i.e., exfoliation of layers (flaking) is observed. During irradiation of samples in the Vikhr PF installation, melting of the surface layer occurs, resulting in a wavy surface relief with the appearance of cracks and craters, i.e., traces of helium gas release and unopened blisters. The sizes of craters are ∼1–2 µm, which is comparable to the dimensions of blisters observed after He⁺ ion implantation in the ILU accelerator. Numerical modeling of the impact of a fast helium ion beam on tungsten in the Vikhr PF installation has been performed. Using methods of X-ray diffraction analysis, the following effects are observed: a decrease in lattice parameters under all modes of ion and plasma flux exposure; varying degrees of changes in the size of the coherent scattering region (CSR) and the magnitude of lattice microstrain and texture. A decrease in the microhardness of tungsten samples after treatment with helium plasma and He⁺ ions in the Vikhr PF installation is detected, which may result from the influence of two competing factors: annealing of defects under intense thermal loads (reduces H_μ ) and thermal stresses arising during the crystallization and cooling of the melted surface layer (increases H_μ ). The mechanisms of the observed phenomena are discussed.

In modern tokamaks, plasma with a vertically elongated cross section is created; however, this configuration is unstable with respect to the vertical position of the plasma, and control systems for the vertical position of the plasma are necessary for the operation of such tokamaks. An important parameter characterizing the capabilities for controlling the vertical position of the plasma is the controllability region. This article assesses the controllability region of the plasma in the KTM tokamak using an HFC coil, taking into account limitations from the power supply. To obtain this assessment, the plasma equilibrium was reconstructed from experimental signals of the tokamak, and a model of plasma motion was constructed on the basis of the reconstructed equilibria. Subsequently, a current control system was simulated for the HFC powered by a voltage inverter in a pulse-width modulation (PWM) mode. The calculated lower estimate of the plasma controllability region was 23 cm, which is sufficiently large for a tokamak with a small plasma radius of 45 cm, and demonstrates the potential for creating an effective plasma position control system using the HFC coil in the KTM tokamak.

The proposed analysis of the unsteady kinetics of helium is based on data and conclusions from the spectroscopic study of helium behavior in the LHD stellarator, specifically on the fact that, in the initial phase of plasma discharge, the behavior of impurities is primarily determined by atomic ionization-recombination (IR) processes rather than particle transport. The temporal evolution of the emission ratios of the spectral lines HeI (447.1 nm) and HeII (468.6 nm) has been used to calculate the time dependence and magnitudes of the recombination rates of helium ions, as well as the temporal evolution of the charge state distribution accompanying the three consecutive stages of discharge initiation: the onset of ECR heating, the injection of helium gas, and the activation of neutral beam heating. It has been found that charge exchange processes with a large number of neutral hydrogen atoms, particularly in excited states, contribute significantly to recombination. Owing to the high values of IR rates for helium, the relaxation time of its charge distributions to quasi-steady-state distributions is less than 0.2 ms, which allows for a simplification of the detailed analysis of helium charge kinetics in the LHD and enables it to be conducted within the framework of a quasi-steady-state problem.

A Monte Carlo model of an experiment with the universal trap of ultracold neutrons at the PIK reactor has been developed. The project assumes that in one installation two traps are installed on the same axis: material and magnetic. By rotating the trap system around an axis, it is possible to carry out gravitational capture of UCNs either into a material or into a magnetic trap. Thus, on one installation it is possible to compare the material and magnetic storage of UCNs under the same conditions. The motivation for such an experiment is the disagreement in the results of measuring the neutron lifetime in material and magnetic traps. As a result of the simulation, the sensitivity of the experiment at the PIK reactor was obtained.

In this report we present machine-learning-based approaches for analyzing Baikal-GVD data. The framework addresses five key challenges in neutrino detection: suppression of air-shower-induced events, rejecting noise activations of optical modules, classification of track and cascade-like hits, reconstruction of neutrino incoming angles, and energy estimation. For each task, we discuss the physical motivation and demonstrate the performance metrics. We introduce a data processing pipeline that incorporates these neural networks and discuss how it can improve both the accuracy and efficiency of data analysis in the Baikal-GVD experiment.

The BM@N experiment is a fixed-target experiment at the NICA accelerator complex and aims to study the interactions of relativistic heavy ions in the energy range corresponding to high baryon density. To identify charged particles in the BM@N, two time-of-flight systems, TOF400 and TOF700, are used. After the 2022–2023 physics run of the experiment, a series of calibration procedures was performed. In the work described are details of the calibration technique as well as evaluation of the system characteristics.

The paper considers the possibility of using 3D printing technology to manufacture structural elements of ionizing radiation detectors. For this purpose, a housing for a scintillation detector with a volume of approximately 73 cm({}^{3}) was printed. Based on this printed housing, a scintillation detector was constructed, utilizing a scintillator made from LAB with additives of PPO (2 g/L) and Bis-MSB (0.02 g/L). The volume of the detector was viewed using a PMT-97. To verify the functionality of the experimental setup, calibration measurements were conducted with a ({}^{137})Cs source, and a background spectrum was collected over 16 hours in the laboratory building of the BNO INR RAS. The results obtained confirmed the feasibility of using 3D printing for the fabrication of structural components of detectors.

The Multi-Purpose Detector (MPD) is a heavy-ion experiment of the NICA complex under construction at JINR, Russia. With heavy-ion collisions in the collider mode, MPD will be able to cover the energy range (sqrt{s_{NN}}=4{-}11) GeV and thus study the baryon-rich region of the QCD phase diagram. The trigger system of the MPD detector includes several subsystems covering the forward and central rapidity regions. In this contribution, we review the performance of the system for the collider mode of operation, and discuss the implications for the system size and the collision energy scans needed for successful implementation of the NICA physics program.