Plasma Physics Reports最新文献

Dependences of sputtering yield of tungsten on the energy of incident alpha particles were obtained in the energy range up to 10 MeV. An equation was proposed that describes the sputtering yield at energies above 100 keV. The results were obtained by numerical simulations using multiparticle potentials. For nuclear alpha particles with an energy of 3.5 MeV, a dependence of the sputtering yield on the incidence angle of the beam relative to the target was derived.

The nonlinear dynamics of axisymmetric radially localized oscillations of the electric potential in a tokamak with stationary toroidal plasma rotation is studied. 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 the plasma equilibrium, and the frequency/growth rate is determined by the stationary rotation velocity. It is shown that the nonlinear dynamics of the electric potential and the associated fluctuations of pressure, density, and velocity of the plasma along the magnetic field within the MHD model have integrals of motion. The evolution of the electric potential and hydrodynamic characteristics of the plasma is calculated for different velocities of stationary plasma rotation and different initial perturbations of the electric field. The regime the initial stage of which corresponds to a linearly unstable ZF is studied in detail. It is shown that, at the nonlinear stage, the potential fluctuations reach amplitude-limited oscillations of both low frequency and GAM. The resulting oscillation spectrum exhibits GAM frequency splitting and intermittency.

The dusty plasma parameters of Saturn’s magnetosphere at different distances from the planet have been considered. Particular attention is paid to the parameters in the vicinity of the satellite Enceladus. The influence of the photoelectric effect caused by the interaction of the dust component of the plasma of Saturn’s magnetosphere with solar radiation on its parameters is considered. Because of the photoelectric effect, situations are possible when dust particles can acquire a positive charge despite the significant distance from the Sun. Both cases are considered: positive and negative charge of dust particles. The conditions under which dust particles can have a positive charge are determined. The dusty plasma parameters of Saturn’s magnetosphere are determined depending on the character of charging of dust particles. A qualitative method for determining situations when dust particles have a positive or negative charge is proposed.

Plasma–dust processes in the vicinity of an active asteroid are analyzed. Distribution functions of photoelectrons, along with altitude dependences of charge, size, and concentration of dust particles, are determined based on the physico-mathematical model self-consistently describing concentrations 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.

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 launching 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.

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.

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.

The energy characteristics (losses of 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 hydrogen two-electrode spark gaps of the subnanosecond range have been studied in a wide pressure range (10–60 atm). The effect of runaway electrons on the energy characteristics of hydrogen spark gaps has been studied. For these purposes, the reflectometry method for measuring pulse voltages in the study of subnanosecond self-sustained discharges in gas is modified as follows. The plasma resistance of the discharge gas gap, which changes with time at the switching stage, is replaced by a constant resistor in those sections of the voltage waveform, 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 voltage drop across the discharge gap measured at the breakdown stage, which cannot be correctly recorded in the subnanosecond range due to the presence of parasitic inductance of the measuring path. The voltage and current waveforms obtained in this way allowed us to calculate the dynamics of power and the total energy introduced into the gas-discharge plasma.

An electromagnetic wave amplifier based on the forced Cherenkov effect of a relativistic thin tubular electron beam in a coaxial waveguide with a plasma-dielectric filling is considered. In the linear approximation, a dispersion equation is derived, amplified frequency domains are defined, and wave amplification factors are calculated. Two maximum amplification modes were studied depending on the beam-dielectric gap and frequency. The nonlinear dynamics of the amplification process was investigated. Amplification efficiencies for different beam currents and different frequencies of the amplified signal were determined. The effect of plasma on wave amplification in a coaxial waveguide with a dielectric insert was studied in detail. The interaction of the beam with the potential Langmuir wave in plasma was shown to affect but slightly the amplification of electromagnetic waves.

The paper describes the numerical simulation of quasi-stationary configurations of current sheets with a given normal component of the magnetic-field, which consists of a thin ion current sheet and its embedded super thin electron current sheet. These sheets were regularly observed during the pre-storm phase of magnetospheric substorms by the MMS satellite mission in the neutral sheet of the near magnetotail of the Earth. A new numerical model is proposed of a stationary current sheet with kinetic description of transient ion populations and electrons forming it, for which the Vlasov equations are solved by the method of characteristics for stationary case and the distribution functions are calculated on regular grids in velocity space, the real charge-to-mass ratio for electrons being taken into account. This model was used to obtain planar symmetric configurations of the super thin current sheet, which agree qualitatively and quantitatively with MMS spacecraft observations.