Plasma Physics Reports最新文献

The article presents the results concerning the cross-sectional energy density distribution of a pulsed ion beam for two types of diodes with electron open drift: with external magnetic insulation (250 kV, 80 ns, 0.6 T) and with self-magnetic insulation of electrons (250–300 kV, 120 ns, 0.8 T). Anode plasma is formed using a breakdown along the surface of the anode dielectric coating (single-pulse mode) or explosive electron emission (with double opposite-polarity pulses). It was found that, when the energy density of the ion beam exceeds ≈0.4 J/cm², periodic spoke-type structures with a step of 3–6 cm in the beam cross section are formed. The processes of formation of such a structure—nonuniform density of anode plasma and self-organization of anode and/or cathode plasma in crossed electric and magnetic fields—are analyzed. It is shown that the formation of local plasma regions in the anode–cathode gap of an ion diode can cause the formation of a periodic structure of the cross-sectional energy density distribution.

The paper presents the results of many years of research carried out in various organizations of the USSR and Russia in the process of developing thrusters with anode layer (TALs) and stationary plasma thrusters (SPTs). They are known under the general name “thrusters with closed electron drift” (TCEDs), since they are developed on the basis of plasma ion accelerators with closed electron drift (ACEDs). TCEDs have come a long way in development. As a result, the SPT has become one of the most widely used electric rocket thrusters (ERTs) and continues to develop. The TAL development has also reached a fairly high level and is close to practical use. Therefore, here we consider the main physical principles and research results that determined the progress in the SPT and TAL development with the aim of their analysis and generalization, as well as assessment of their applicability for further development such thrusters. A brief overview of the main stages of the SPT and TAL development and the results achieved at these stages are given. It is shown that the main problem of their further development is to ensure both high thrust efficiency and a long service life. It is also shown that the main factor limiting the service life of TALs and SPTs is the ingress of accelerated ions onto their structure elements; therefore, in order to control the ion motion, it is first of all necessary to understand the patterns of electric field formation in TCED discharges. New properties of TCED discharges and the peculiarities of electric field formation are revealed and their known properties are clarified, which determine the thickness and position of the acceleration zone with the main potential drop in the discharge and the flows of accelerated ions onto the thruster structure elements. The methods of controlling the thickness and position of the acceleration zone in an TCED by varying the magnetic field characteristics, successfully tested at the second stage of the SPT and TAL development, are considered and analyzed. It is shown that these methods make it possible to effectively control the operation of an TCED and its characteristics, and physical conditions ensuring the efficiency of their application are determined. Physical conditions for the implementation and justification of the feasibility of completely removing the acceleration zone from the thruster as the main direction of modern TCED development are determined, taking into account the analysis of the properties of the discharge and the peculiarities of electric field formation in an TCED. The main conclusions on the issues considered are given.

An overview of the functional dependences (formulas) for describing the properties of atomic particles sputtered during ion bombardment of the surface of a solid body is presented. The dependence of sputtering coefficients on the energy and angle of incidence of the bombarding particle is considered. The energy spectra and average energies of sputtered particles are presented. Formulas for calculating the quantities under consideration are proposed by the example of a target made of tungsten and hydrogen isotopes as projectiles. These data are necessary to estimate the entry of sputtered tungsten atoms as an impurity into a hot plasma using transport codes. When the tungsten impurity concentration is higher than the critical one, it is impossible to carry out a controlled thermonuclear reaction with the planned energy output in the ITER tokamak reactor. Sputtering coefficients also play an important role in simulating the entry of impurities into plasma facilities as a result of the interaction between hydrogen fuel atoms and the materials of the divertor and the first wall.

Probe diagnostics of ion energy distribution and ion current density in the plasma plume of electric propulsion is considered. A detailed numerical and experimental comparison is presented of a new, high dynamic range retarding potential analyzer (HDR RPA) and a conventional gridded RPA probe applied to a plume of a hall effect thruster (HET) operating in different modes. Simulations show the disadvantages of the gridded retarding potential analyzer design and the advantages of the HDR RPA. By means of numerical modeling, the peculiarities of using the HDR RPA are also investigated in detail and preliminary conclusions regarding the probe accuracy are drawn. The final part of the paper shows the results of joint tests of the two probes at those plasma parameters where the gridded probe works most accurately, with a confirmed maximum error of 5%.

Comparative analysis of time evolutions of plasma macro- and microparameters during spontaneous and induced transient processes in the classical quasi-stationary stellarator L-2M is presented. Plasma heating was performed in the electron cyclotron resonance heating (ECRH) regime at the second harmonic of electron gyrofrequency under conditions of high specific energy input in the power range of 0.8−2 MW/m³. Spontaneous transient processes are observed at constant heating powers, and induced ones are initiated by a stepwise increase or decrease in heating power. Correlation between time evolutions of plasma macroparameters (primarily the energy lifetime) and the parameters of plasma turbulence is searched. Physical models of the phenomena that determine dynamic changes in plasma macroparameters are presented. Analysis of the data of high-frequency diagnostics made it possible to clear up the action of MHD and kinetic instabilities on transient processes in the stellarator hot plasma, as well as the role of plasma-wall interaction.

A theory of large-scale flows of rotating partially ionized space and astrophysical plasma in the approximation of the Hall magnetohydrodynamics is developed. Partially ionized rotating plasma describes large-scale processes in the exoplanetary atmospheres of hot Jupiters, the thermospheric–ionospheric system of planets and the Earth, in the protoplanetary disks, along with many other objects of heliophysics and space physics. The derived equations contain nontrivial terms describing the influence of rotation on the Hall current and ambipolar plasma diffusion in addition to the traditional Coriolis force acting upon momentum of the plasma’s center of mass. Linear flows are analyzed in the simplest case when gravity is neglected. The dispersion relations for modified Alfvén waves, rotating fast and slow acoustic waves, along with modified whistler waves, are obtained. The slow acoustic waves represent a new type of flows driven by the Coriolis force. The fast acoustic waves correspond to conventional acoustic waves in the absence of rotation.

Over the many decades of studying the electric explosion of thin wires (EEW), researchers have developed and accepted certain notions about this process. Despite the lack of proof behind certain established assertions and, sometimes, their contradiction with the results of recent experiments, they are still widely used to describe and interpret new data. In the first place, this concerns the concept that the EEW is a fast evaporation of metal as a result of the dissipation of Joule energy inside it. Another fundamental notion that is used during the analysis of the experimental results and in model calculations is the uniform distribution of matter along the cross section of the wire core during the explosion. To date, the nature and mechanism of the appearance of strata, i.e., the periodicity observed in many images of the EEW, remain unexplained. Using the traditional notions of the EEW, even in experiments conducted at a high level, does not allow one to correctly interpret the obtained results and, as a whole, does not facilitate the progress in understanding the complicated physics of the process of wire explosion. Therefore, the traditional concepts of the EEW have long required a revision. This work summarizes the results of modern research in this area and considers its relation to the previous works. It also proposes new approaches to the studies of the EEW dynamics and to the understanding of the processes of energy transformation in matter during its rapid heating by the electric current.

Ion cyclotron resonance heating is considered as one of the methods of additional heating of plasma and production of the non-inductive current in the T-15MD tokamak. To transfer the maximum power to the plasma, it is needed to know impedance of an antenna–plasma system, to match it with impedance of an RF power generator and its transmission line. The work is devoted to the development of a code for the calculation of antenna impedance of the ICR heating system of plasma in toroidal magnetic traps. To find impedance of the antenna–plasma system in the simplified geometry of antenna consisting of conductive plates, the wave equation is solved in the “cold” plasma approximation, and the spectrum of the RF power emitted by antenna is calculated. The dependences of the impedance of the antenna–plasma system on distances between antenna and the Faraday screen and between the Faraday screen and the plasma are obtained for the geometry of the T-15MD tokamak. Two-dimensional distribution of electric field of a wave in the plasma is obtained.

A new method is proposed for measuring the electron plasma temperature at the GOL-NB facility. The method is based on measuring the ratio between the intensities of the spectral lines emitted by the fast atoms injected into the plasma. The beams of fast hydrogen atoms used for heating the plasma at the GOL-NB facility contain not only atoms with a full energy (E) but also atoms with fractional energies (E/2, E/3, E/18) that appear as a result of the dissociation of the H(_{2}^{ + }), H(_{3}^{ + }), and H₂O⁺ molecular ions. The spectral lines of the beam components with these energies (and, in particular, the hydrogen H_α line) can be resolved due to the Doppler shift caused by the difference between the atom speeds. For atoms with low energy, the excitation that leads to the photon emission occurs only due to their collisions with thermal electrons, while for atoms with high energy, a sufficient deposition into their excitation is given by their collisions with the plasma ions. This is why the ratio between the intensities of the lines of different beam components depends on the plasma electron temperature, and thus, it can be used to measure this temperature. At the beam energy of 24 keV, the proposed method can be used to measure the electron temperature in the range of up to 40 eV, which is of interest for the current experiments conducted at the GOL-NB facility. Note that measurement of the electron temperature higher than 20 eV requires that the ratio between the spectral line intensities be measured with an accuracy of the order of one percent, and that the attenuation of the neutral beam that passes through the plasma be measured with the same accuracy. The proposed method can be used at other fusion facilities that use fast hydrogen atom injection to measure the temperature of the edge plasma.

The influence of dust grains on soliton reflection in the presence of trapped electrons in an inhomogeneous plasma is investigated. We have considered a plasma model having ions, trapped electrons, and negatively charged dust particles. Here, the reductive perturbation theory (RPT) is employed to obtain the modified Korteweg–de Vries (m-KdV) equation. The solution of m-KdV equation indicates the solitary wave solution in the inhomogeneous plasma system. The solitary wave solution signifies the various effects of dust particles in inhomogeneous plasma. We have also discussed the different modes of soliton propagations during soliton reflection in the presence of inhomogeneity density gradients.