Vol 45, No 7 (2019)

Charged particle motion in the regions of magnetic islands and near-separatrix ergodicity of magnetic field lines in the Т-15 tokamak is studied numerically. The trajectories are calculated by integration of exact three-dimensional equations of motion for trapped and passing charged particles starting at different pitch angles. It is shown that the presence of resonant magnetic perturbations qualitatively affects the trajectories of passing particles. In the region of magnetic islands, the orbits of passing particles acquire an island structure, while in the region of the near-separatrix ergodicity of magnetic field lines, the orbits are stochastized. It is shown that magnetic perturbations insignificantly affect trapped particle motion. Even in the absence of magnetic surfaces, the trajectories of trapped particles are regular and their cross sections have the shape of a standard banana orbit. The possibility of charged particles to pass between regions with different magnetic topologies is analyzed.

A possibility of up–down asymmetry of the profiles of the edge plasma parameters in a symmetric double-null divertor configuration in the case of impurity seeding is found by computational modeling. The physical mechanism of such a symmetry violation, related to radiation-condensation instability, is proposed. This effect can reduce the would-be advantage of the double-null configuration in the power load spreading over a larger area, which is vital for fusion reactor projects.

The densities of NeI atoms and XeII ions in the PS-1 mirror system were measured by the method of laser-induced fluorescence (LIF). Schemes of levels for LIF measurements of the density are proposed. Models for numerical processing of the obtained LIF signals are developed. The electron temperature and plasma density were also measured using Langmuir probes.

The motion of the outer boundary of a quasi-spherical tungsten wire array at currents of 2−4 MA was studied experimentally. It is shown that the outer boundary shifts later than it is predicted by simulations by the heterogeneous array model. The instabilities developing at the boundary of the quasi-spherical array are similar to those occurring in a cylindrical array made of the same material. It is found that, in spite of the different time behaviors of the inductances during implosions of quasi-spherical and cylindrical arrays, the energies required to compress these arrays to ~0.4 of the initial radius differ insignificantly.

The spectral composition of high-power microwave radiation of the plasma relativistic oscillator in the range of 1−4 GHz was studied experimentally as a function of the plasma density and the cavity length and configuration. The duration of the generated microwave pulse was in the range of 250−400 ns, and its total energy reached 15 J. The main features of the spectral composition for different cavity configurations are explained.

Time evolution of the parameters of output radiation of a plasma relativistic microwave oscillator (PRMO) based on the Sinus 550-80 accelerator during a single relativistic electron beam (REB) pulse was studied experimentally. Analysis of the experimental data was accompanied by numerical simulations under conditions close to the experimental ones. It is shown that qualitative changes in the parameters of the PRMO output radiation are associated with a change in the generation mode. The first half of the REB pulse is characterized by the maximum output radiation power and a broadband spectrum consisting of a great number of harmonics. The nonlinear beam–plasma interaction limits the growth of the field amplitude, decreases the number of plasma electrons, and leads to the emergence of longitudinal plasma inhomogeneity. The appearance of an ion background in the drift tube volume and the formation of a radially nonuniform plasma waveguide alter the conditions of beam–plasma interaction in the second half of the pulse. The second half of the REB pulse is characterized by a decrease in the output microwave power and the narrowing of the generation frequency band. Spectral analysis demonstrates preservation of a stable narrow spectral component throughout the microwave pulse.

Based on the 16-moment MHD transport equations, the propagation of linear waves in an anisotropic homogeneous cosmic plasma is considered. A general dispersion relation is derived with allowance for two plasma components (electrons and protons) and heat flux along the magnetic field. This dispersion relation is a generalization of the previously studied cases of one-component (ion) plasma. The case in which the effects associated with the heat flux are ignored is analyzed in more detail. In the limit of longitudinal propagation, the wave modes fully consistent with the modes known in the low-frequency kinetic theory of collisionless plasma are classified. Firehose and mirror instabilities are analyzed. It is shown that taking into account the electron component modifies the growth rates and thresholds of instabilities.

The Jeans instability of collisional magnetized dusty plasmas is examined incorporating polarization force, charge variation of dust grains, and radiative cooling of ion and electron species. The collisional effects of dust grains with neutrals are considered with sufficient background of neutral particles. A general dispersion relation is obtained using normal mode analysis technique which is found to be modified due to polarization force, dust charge fluctuation, and radiative effects of electrons and ions. The analytical discussion of general dispersion relation is presented in parallel and perpendicular mode of propagation. The Routh Hurwitz criterion is applied to analyze the stability of the considered system. We report the existence of a modified cyclotron mode in parallel propagation and a purely collisional mode in perpendicular propagation along with the gravitational mode. These modes are discussed analytically, as well as numerically, to show the importance of different parameters considering different situations. The implications of the result have been discussed for the molecular clouds.