Vol 51, No 6 (2025)
TOKAMAKS
PROBE MEASUREMENTS IN EXPERIMENTS WITH ADDITIONAL WORKING GAS PUFFING INTO FRONTAL REGION OF LOWER HYBRID ANTENNA OF THE FT-2 TOKAMAK
Abstract
In the experiments at the FT-2 tokamak, it was ascertained that the additional puffing of working gas into the region immediately adjacent to the radiating antenna suppresses the development of parametric instability, which is considered to be the main obstacle to efficient penetration of the lower hybrid wave into the inner regions of the tokamak plasma. Using probe measurements, radial profiles of electron density and temperature in the scrape-off layer (SOL) were obtained, as well as their changes during the lower hybrid pulse were traced. It was shown that local gas puffing causes toroidal inhomogeneity of the edge plasma parameters. By means of performing direct measurements, the effect of plasma "forcing-out" from the frontal region of the radiating antenna under the action of ponderomotive force in the field of the introduced wave was detected. The effect of ponderomotive force on the edge plasma parameters and, as a consequence, on the antenna-plasma coupling efficiency should be taken into account in large-sized facilities at high powers.
Fizika plazmy. 2025;51(6):581-590
581-590
NONLINEAR DYNAMICS OF LINEARLY UNSTABLE n = 0 ELECTROSTATIC PERTURBATIONS IN CONVENTIONAL TOKAMAK PLASMAS
Abstract
The nonlinear dynamics of axisymmetric radially localized oscillations of the electric potential in a tokamak with stationary toroidal plasma rotation is investigated. In the linear approximation, these oscillations split into two independent branches: geodesic acoustic modes (GAMs) and low-frequency zonal flows (ZFs). The stability of the latter is determined by the specifics of plasma equilibrium, and the frequency/growth rate – by the velocity of stationary rotation. It is shown that the nonlinear dynamics of the electric potential and the associated fluctuations of pressure, density, and longitudinal plasma velocity within the MHD model has integrals of motion. The evolution of the electric potential and hydrodynamic plasma characteristics is calculated for different velocities of stationary plasma rotation and for different initial values of the electric field perturbations. The regime, which initial stage corresponds to linearly unstable ZF, is studied in detail. It is shown that at the nonlinear stage, the fluctuations of electric potential reach amplitude-limited oscillations of both low frequency and GAM. The resulting oscillation spectrum exhibits GAM frequency splitting and intermittency.
Fizika plazmy. 2025;51(6):591-611
591-611
Tungsten Sputtering by Alpha Particles
Abstract
The dependences of the tungsten sputtering yields on the energy of incident alpha particles in the range up to 10 MeV are obtained. A formula is proposed that describes the behavior of the sputtering yield at energies above 100 keV. The results are obtained by computer modeling using multiparameter potentials. For thermonuclear alpha particles with an energy of 3.5 MeV, the dependence of the sputtering yield on the angle of incidence of the beam on the target is obtained.
Fizika plazmy. 2025;51(6):612–615
612–615
BEAMS IN PLASMA
Rotation of Bulk Potential Waves in Cylindrical Waveguide with Partially Inhomogeneous Plasma Filling
Abstract
Propagation of bulk potential waves formed by superposition of helical harmonics with opposite azimuthal wavenumbers in a column of magnetized plasma is studied theoretically. The spectrum of bulk waves is calculated for a Gaussian density distribution. It is demonstrated that radial inhomogeneity of plasma in a metal waveguide with a vacuum gap at a certain frequency leads to a change in the direction of the bulk wave pattern rotation perpendicular to the waveguide axis.
Fizika plazmy. 2025;51(6):616--623
616--623
PLASMA DYNAMICS
NUMERICAL SIMULATION OF PLASMA JET EXPANSION IN A LABORATORY EXPERIMENT
Abstract
The results of numerical simulation of plasma jet expansion into a rarefied medium in a two-temperature gas dynamics model with separation of electron and ion temperatures are presented. The results obtained using two independent numerical methods are compared with the data of a laboratory experiment on jet injection into a vacuum chamber. It is shown that the ion and electron temperature of the main mass of the jet is in equilibrium. Estimates of the injection scenario are given taking into account the deformation of the generator nozzle.
Fizika plazmy. 2025;51(6):624-634
624-634
PLASMA ELECTRONICS
Suppression of Self-excitation in a Plasma Microwave Amplifier with Coaxial Geometry Using an Extended Microwave Absorber
Abstract
The problem of radiation amplification in a plasma microwave amplifier with coaxial geometry with an absorber is considered. The role of the absorber is to suppress parasitic feedback, which can lead to self-excitation of the system, while the presence of the absorber leads to a modification of its electrodynamic properties. Spatial increments of beam-plasma instability are calculated and regions of parameters are determined when self-excitation of amplifier does not occur. Influence of absorber on efficiency of conversion of kinetic energy of electrons into energy of microwave oscillations is estimated.
Fizika plazmy. 2025;51(6):635–642
635–642
SPACE PLASMA
Experimental simulation of the features of propagation of auroral kilometric radio emission in inhomogeneous magnetoplasma
Abstract
The high-frequency wave propagation in homogeneous and inhomogeneous plasma at frequencies close to electron cyclotron resonance has been laboratory simulated. In the experiment the electron cyclotron frequency is higher than the plasma frequency but lower than the radiation frequency, which corresponded to the conditions of the propagation of auroral kilometric radio emission in the Earth's magnetosphere recorded by high-orbit satellites at a large distance from the generation region. The features of channeling magnetoplasma modes in an artificial magnetically oriented low-density plasma duct are studied. Experimental results show that plasma irregularities with transverse dimensions smaller than the wavelength in vacuum are effective channels for the transfer of fast waves along the magnetic field.
Fizika plazmy. 2025;51(6):643–651
643–651
ПЫЛЕВАЯ ПЛАЗМА
Plasma in the Vicinity of an Active Asteroid
Abstract
Plasma–dust processes in the vicinity of an active asteroid are analyzed. Distribution functions of photoelectrons, along with altitude dependences of charge, size, and number density of dust particles, are determined based on the Physics and Mathematics model self-consistently describing number densities of photoelectrons and dust particles above the illuminated part of an active asteroid. It is demonstrated that processes related to gas flow from the surface areas of the asteroid containing water represents an important factor that has an impact on formation of the plasma–dust system in the vicinity of an active asteroid. The gas flows make levitation of small particles impossible. On the other hand, it turns out that relatively large dust particles can be considered levitating above the asteroid surface.
Fizika plazmy. 2025;51(6):652–658
652–658
Parameters of dusty plasma in Saturn's magnetosphere
Abstract
The parameters of dusty plasmas of Saturn’s magnetosphere at different distances from the planet are considered. Special attention is given to the parameters near the moon Enceladus. The influence of the photoelectric effect caused by the interaction of dust component of Saturn’s magnetospheric plasma with solar radiation on its parameters is discussed. It is demonstrated that due to the photoelectric effect, even though far away from the Sun, there may be situations where dust particles can gain a positive charge. Conditions under which dust particles could carry a positive charge were defined. A qualitative method was suggested for identifying scenarios when dust particles carry either positive or negative charges.
Fizika plazmy. 2025;51(6):659–666
659–666
LOW TEMPERATURE PLASMA
Energy Characteristics of Self-Sustained Subnanosecond Discharge in Hydrogen
Abstract
In a wide range of pressures (10–60 atm) the energy characteristics (losses of the switched energy in the spark gap, which go to light emission, ionization, excitation and heating of the working gas during the development of plasma processes; as well as the instantaneous released power, which serves as an energy source for the above processes) of two-electrode hydrogen spark gaps of the subnanosecond range are investigated. The influence of runaway electrons on the energy characteristics of hydrogen switches is investigated. For these purposes, a modification of the reflectometry method for measuring pulse voltages in the study of subnanosecond self-sustained discharges in gas is proposed. It consists in the fact that the resistance of the plasma of the discharge gas gap, changing in time at the switching stage, is replaced by a constant resistor in those sections of the voltage oscillogram, where the characteristic ionization time exceeds the duration of the voltage pulse applied to the gap by more than an order of magnitude. This made it possible to reconstruct the trailing edge of the voltage pulse on the discharge gap, measured at the breakdown delay and breakdown stages, which is usually lost in the subnanosecond range when measuring such oscillograms due to the presence of parasitic inductance of the measuring path. The voltage and current oscillograms obtained in this way allowed us to calculate the dynamics of the power and the total energy introduced into the gas-discharge plasma.
Fizika plazmy. 2025;51(6):667-678
667-678