Physics of Atomic Nuclei最新文献

The upgraded near neutrino detector of the T2K experiment is briefly described. The central part is the 3D scintillator fine-grained detector (SuperFGD). The detector comprised of about 2 million (1times 1times 1) cm({}^{3}) plastic scintillator cubes with three orthogonal holes for wavelength shifting fiber readout. It will be used as an active neutrino target to detect charged particles and photons. A combination of SuperFGD with the other subdetector systems in the ND280 detector provides a possibility to detect more neutrino events (due to an additional active target), as well as to increase the accuracy of the neutrino events reconstruction. In this work, the results of Monte Carlo simulation of the interactions of electron and muon neutrinos in the updated ND280 complex are presented. The efficiency of matching tracks between SuperFGD and other subdetectors of the upgraded ND280 will be discussed.

The (e^{+}e^{-}topi^{0}gamma) cross section has been measured in the center-of-mass energy range from 1000 to 1060 MeV with the SND detector at the VEPP-2000 electron-positron collider. At the maximum of the (varphi)(1020) resonance the systematic uncertainty of the cross section measurement is 1.3%, and the statistical uncertainty is 2.2%. To date, this is the most accurate measurement of the (e^{+}e^{-}rightarrowpi^{0}gamma) cross section. As a result of data approximation with the vector dominance model the decay branching ratio (B(phitopi^{0}gamma)=(1.452pm 0.024pm 0.067)times 10^{-3}) has been measured.

New stable heavy particles with even negative charge (X^{-2n}) arise in several extensions of the Standard Model. The Thomson-like neutral bound states (X) He called dark atoms can be dark matter candidates, explaining the puzzles of direct dark matter searches. However, at present there is no comprehensive description of their formation at early stages of the cosmological evolution. The process of the (X^{-2n}) excess generation depends significantly on a model, pending on the electroweak properties of (X)-particles. If these particles have nontrivial (SU(2)) electroweak charges, such excess can be balanced with baryon asymmetry by sphaleron transitions. The successive development of the nucleosynthesis, modified by the presence of dark atoms, is determined by their nuclear interaction with the baryonic matter. We approach these open questions of dark atom cosmology in the present work.

Requirements for generation of the resonant magnetic fields in tokamaks for controlling magnetohydrodynamic (MHD) plasma perturbations, stabilizing edge localized modes (ELM), and suppressing accelerated electron beams are considered. A preliminary design of a system for generating external resonant magnetic fields on the T-15MD tokamak is considered. The design is based on a system of 48 multipole coils located inside a vacuum vessel (16 windings around the equatorial plane, 16 windings in the upper cone, and 16 windings in the lower cone) to create resonant magnetic fields with poloidal and toroidal harmonics m = 1–8, n = 1–4.

The similarity of spatial profiles of electron temperature T_e and electron density n_e at the quasi-stationary stage of electric current in plasma in 21 discharges in the Globus-M2 tokamak have been statistically analyzed. The analysis is similar to that carried out earlier with JET tokamak data. The existence of universal profiles of T_e and n_e depending on the normalized minor radius of the plasma column ρ has been shown. The discharge universal profiles (DUPs) are obtained by dividing the space-time-dependent profile by the space-averaged value of this parameter in the region ρ ≤ ρ_max = 0.5–1 and subsequent averaging over time at the quasi-stationary stage of each discharge. The machine universal profiles (MUPs) are obtained by additional averaging over time of all discharges. It has been shown that, in all considered discharges, the time-averaged ({{{{tilde {sigma }}}}_{{{{T}_{{text{e}}}}}}}), the relative root-mean-square deviations of the T_e profile from the DUP and MUP, at ρ_max = 0.8 on radii of ρ = 0.1–0.7 do not exceed 10%, and at ρ = 0.9, accuracy decreases. Similar values of spatially averaged ({{{{tilde {sigma }}}}_{{{{T}_{{text{e}}}}}}}) exceed 10% only at one of 136 time points of all considered discharges. A similar picture has been observed for n_e profiles. A comparison of the MUP for T_e in JET and Globus-M2 has shown some difference in profiles, maximal at small ρ. Using the SvF method of balanced identification, the accuracy of the representation of T_e(ρ, t) as the product of two functions of only one variable, time and coordinate, has been found. The results illustrate the high degree of plasma self-organization in tokamaks.

A method for calculating sputtering of the tokamak first wall by fast charge-exchange neutral atoms of hydrogen isotopes in the near-wall plasma has been proposed. The application of the method has been shown by the example of sputtering of the assumed first-wall materials under the near-wall plasma conditions in the ITER tokamak. Using the BM1D2V code based on the ballistic model of hydrogen recycling kinetics in the tokamak main vacuum chamber, the velocity distribution function (VDF) of neutral atoms and molecules of hydrogen isotopes in the near-wall plasma has been calculated. Using the calculated VDFs, the sputtering rate of beryllium, tungsten, and boron from the surface of the first wall of the tokamak vacuum chamber in a typical ITER divertor operating mode has been estimated. The reflection coefficients of atoms of hydrogen isotopes from the first wall used in the ballistic model and the sputtering coefficients have been calculated using the SDTrimSP code.

The study of critical current anisotropy with respect to the direction of the external magnetic field is fundamental for optimizing the design of superconductor-based devices, particularly magnetic systems in controlled fusion facilities. This article provides a concise critical overview of modern methods for analyzing the angular dependence of the critical current in technical superconductors, with a focus on second-generation high-temperature superconducting (HTS) tapes. These methods are grounded in three previously proposed models: scaling, vortex path, and anisotropic pinning. Experimental results of angular dependence studies for HTS-2 tapes with varying chemical compositions are presented. Several distinctive features are highlighted, including the nontrivial effect of rare earth element substitution in the HTS composition on the pinning landscape, peak asymmetry, and critical current dependence on the Lorentz force direction. The analytical methods discussed are then applied to the experimental data. The quality of model approximations was evaluated using the coefficient of determination, adjusted for the number of fitting parameters. The analysis reveals fundamental differences in the interpretation of features of angular dependences depending on the chosen model. It is concluded that no universal approach exists to reasonably interpret observed features while linking them to the defect structure of HTS materials. This highlights a significant gap in current understanding of superconducting electromagnetic behavior and underscores the need for further research.

A simple TOREQ (Toroidal Equilibrium) code for solving the Grad–Shafranov equation, applicable for a tokamak with any aspect ratio, any (positive and negative) triangularity, any elongation with a fixed D-shaped or with X-point boundary, and with any arbitrary functions on the right-hand side of the equation has been described. The results of calculations of equilibrium parameters with published data have been compared.

Two experimental campaigns were carried out at the T-15MD tokamak in 2023. The main goal of the experiments was to obtain discharges with a plasma current in the range of hundreds of kiloamperes and a duration of about several seconds. To obtain equilibrium magnetic configurations and ensure stable discharge scenarios, a series of calculations using the TOKSСEN code was carried out before the start of the experiments and during the campaign. Taking into account the calculations carried out during the experiments, stable configurations of the plasma cord with a current of up to 250 kA and a duration of up to 2 s were realized.

A new ray tracing code, Fast_mp_ECH_startup, for calculating the multipass electron cyclotron (EC) absorption of injected radiation in plasma at the initial stage of discharge in tokamaks has been presented. For conditions close to the initial stage of discharge in tokamak reactors, the EC absorption efficiency calculated by the new code has been compared with calculations using the ray-tracing code GENRAY and with calculations based on the model of isotropic and homogeneous mixing of the injected radiation after one or more reflections from the vacuum chamber wall.