Plasma Physics Reports最新文献

We present the results of numerical studies of the influence of evaporation of anode material on the main characteristics of an arc discharge. Calculations were carried out for an arc discharge in helium as a buffer gas with high-melting-point (using graphite as an example) and low-melting-point (using copper as an example) anodes. The dependences of the main arc-discharge parameters on current density are presented. It is demonstrated that intense evaporation of particles of the anode material into the discharge gap occurs upon reaching the melting point of the anode surface. As a result, the plasma-forming ion is replaced, i.e., the carbon ion in the case of the graphite anode or a copper ion in the case of the copper anode becomes dominant. In the process, a jump in the potential is observed in the dependence of voltage on current density (the volt–ampere characteristic, VAC). Distribution of the main plasma parameters along the discharge gap is presented for different points in the VAC.

Heavy ion beam probe (HIBP) is a unique plasma diagnostics that makes it possible to measure the electric potential φ of high-temperature plasma and its fluctuations (tilde {varphi }), as well as the density ({{tilde {n}}_{e}}) and poloidal magnetic field ({{tilde {B}}_{{{text{pol}}}}}) fluctuations. Position of the point of performing measurements in the plasma vertical cross-section depends on the beam energy and angle of its entrance into the plasma. The variation of these two parameters makes it possible to construct a two-dimensional (2D) detector grid, which covers the domain of possible measurements. The measurement results obtained in the detector grid points provide for constructing 2D distributions of plasma parameters. For the OH and ECRH stages of the T-10 tokamak shots, 2D distributions of the plasma electric potential are presented for the regime with the on-axis magnetic field of B_t = 2.2 T, plasma current of I_pl = 230 kA, line-average density of ({{bar {n}}_{e}})≈ 1.1 × 10¹⁹ m^–3 and off-axis ECRH power of P_ECRH = 1.7 MW.

The results of an experimental study of the initiation, development and maintenance of a plasma surface discharge initiated by microwave (microwave) radiation of a gyrotron (75 GHz, 300 kW, 6 ms) in air under normal conditions on the surface of a quartz substrate with metal inclusions are presented. It is shown that the velocity of the propagation of the discharge ionization front reaches 40 m/s, which corresponds to the thermal conduction propagation mechanism. In this case, the maximum calculated gas temperature of the plasma reaches 5500 K, which leads to the sublimation of metal inclusions. For the first time, the plasma parameters of a surface microwave discharge on metal-dielectric targets, which have been used in various aeroplasma and plasma-chemical applications, are presented.

Using the Korteweg–De Vries equation, for background plasma, the distribution functions perturbed by ion-acoustic solitons are calculated. For describing the perturbed distribution functions, the explicit formula is obtained, which is suitable for practical applications. The results are compared with the analytical calculations and simulation results obtained previously.

The exosphere of Mercury, which has much in common with the exosphere of the Moon, can also contain suspended dust particles, which, under the action of intense solar radiation, acquire positive charges and form one of the components of the dusty plasma system. In addition to dust particles, there are photoelectrons above the planet surface, formed as a result of interaction of solar radiation with the planet surface, as well as with suspended dust particles. Mercury, unlike the Moon, has its own magnetosphere, which affects the parameters of dusty plasma system. The dusty plasma parameters near the Mercury surface can vary depending on the distance from the planet to the Sun, which considerably changes when the planet moves along the elongated orbit, and also depending on the localization of the region under consideration on the planet surface. Thus, near the magnetic poles, the solar wind can reach the planet surface, which must be taken into account when determining the plasma parameters. Far from the magnetic poles, the effect of the solar wind can be neglected. In the dusty plasma near the surface of Mercury, one can expect the development of linear and nonlinear wave processes. In this paper, nonlinear waves are considered, namely, dust acoustic solitons and nonlinear periodic waves. The profiles of potentials of high-amplitude solitons and nonlinear periodic waves are obtained, as well as the soliton amplitudes as functions of the altitude above the planet surface and soliton velocity.

A molecular dynamics simulation of a system of massive charged particles on a compensating homogeneous background confined by a spherical surface has been carried out. A crystallized cluster is a set of nested spherical shells of almost the same structure and a core. It is shown that cluster melting is a combination of shell and core melting. It is found that the values of the Coulomb coupling parameter Γ corresponding to these two types of melting do not depend on the cluster size. Methods for determining Γ based on the Wigner–Seitz cell model are discussed. It is shown that the estimate based on the root-mean-square deviation of a particle from the center of its cell is unreliable due to the self-diffusion of particles. A relation is proposed that defines Γ in terms of the root-mean-square velocity and acceleration of the particle and does not include the root-mean-square deviation of the particle from its average position. It is shown that this relation is satisfied with high accuracy not only for the crystallized, but also for the liquid state. Thus, it has been demonstrated that the Wigner–Seitz cell model is applicable to the strongly inhomogeneous system under consideration.

The thermonuclear fusion between fast (super-thermal) particles injected in plasma as a neutral beam and the ions of the background plasma is expected to be the main source of fusion neutrons in FNS (fusion neutron source) design based on tokamak. Neutral beam contribution in fusion reactivity and in the total neutron yield depends on the high-energy ion fraction in the integral energy distribution. NESTOR code [1] calculates nuclear fusion rates in the FNS plasma volume, taking into account an external source of high-energy fast ions. Neutral beam model reproduces in detail the actual beam structure in phase space at the injection port plane; while the fast ion distributions in magnetically confined plasma are calculated using a combination of slowing-down classical formulae and magnetic field topology in the tokamak chamber. Here we discuss the issues relevant to the overall neutron production and the contribution of fast ions to the neutron output in plasma.

The semiempirical quasi-classical method of approximation of the ionization potentials used earlier for multiply charged ions of the elements with medium and high atomic number Z is applied to ions of elements with atomic numbers in the range of (85 leqslant Z leqslant 110) and number of electrons in the range of (1 leqslant {{N}_{e}} leqslant 78). The discovered simple trends allow using a relatively accurate (to within 1–2%), based on two small tables, polynomial approximation of the available and lacking data on the ionization potentials in the NIST tables for all multiply charged ions in the atomic-number range under consideration. An improvement in the applicability conditions of the quasi-classical approximation with increase in the atomic number is demonstrated.

Three-dimensional plasma-dust formations consisting of calibrated dust particles differing in sizes and material densities are studied. The characteristic features of the structures formation in stratified glow discharge were studied, as well as their shapes and dynamics in the external magnetic fields. From several types of powders, the spatially separated double structures were obtained, which filled the dust trap, being located in different stratum phases. For each part of the structure, the average rotational velocities were obtained as functions of the magnetic field. In the range, in which the rotation mechanism depends on the particle size and the ion drag force is dominant, the rotational velocity was numerically estimated with allowance for the parameters variation along the stratum.

2D and 3D simulations of the penetration of neutral particles into the plasma with parameters corresponding to the ohmic heating regime in the L-2M stellarator were performed, and the simulation results were compared. Radial distributions of neutrals density in plasma and model energy spectra of fluxes of charge-exchange atoms escaping from the plasma were obtained. For the conditions of the ohmic heating regime in the L-2M stellarator, the limiting plasma densities were determined, above which it is necessary to take into account the recombination processes when performing simulations. Comparison of the model energy spectra of fluxes of charge-exchange atoms escaping from the plasma with experimental data made it possible to construct the radial distributions of the neutrals density in absolute units. In this case, the calculated density of neutrals at the plasma axis turned out to be ~10¹⁵ m^–3, which is four orders of magnitude less than the density of charged particles 10¹⁹ m^–3.