Vol 45, No 2 (2019)

It is well known that heat exchange between the hot plasma and solid wall of a magnetic fusion reactor (tokamak or stellarator) depends, to a great extent, on local disturbances of its magnetic configuration, which occur under the action of resonant magnetic perturbations. One possible reason for their development in tokamaks is splitting of an originally axisymmetric current channel into separate filaments. Among negative consequences of such filamentation, there are spatial modulations of the plasma density and temperature, which can considerably increase local heat loads on the tokamak intrachamber elements. This study draws attention to the fact that one of the most dangerous manifestations of current filamentation in tokamaks is the formation of so-called “positive” magnetic islands, which are clearly observed during the development of internal disruptions in the form of “hot spots”—local hot dense helical plasma structures formed in the central region of the plasma column just before the major disruption. An increase in the heating efficiency and improvement of plasma confinement within magnetic islands (which are, in fact, closed magnetic configurations) could explain energy balance in such structures. In this article, stability of such structures and possible sources of initial current disturbances initiating their formation are discussed as illustratively as possible on the basis the initial physical principles, which, in the author’s opinion, can be useful for the experimenters who start solving problems of plasma–wall heat exchange under real tokamak conditions. A number of the well-known experimental observations that can be explained in the framework of this concept are discussed. It is argued that the concept of positive magnetic islands makes it possible to interrelate the sequence of MHD events resulting in the tokamak major disruption.

Results from studies of plasma production and confinement in Galatea multipole magnetic traps at the Russian Technological University MIREA are presented. The magnetic systems of such traps are considered. It is shown that it is possible to design a system in which plasma bunches and neutral atomic beams are injected along the major radius of the torus. Different methods of plasma production in such traps are studied. It is shown that plasma production by means of an electric discharge is inefficient. The process of loading of the trap with plasma by injecting a plasma bunch is studied in detail. The parameters of the plasma bunch at which it is efficiently captured by the trap are determined. The azimuthal diamagnetic current arising after the plasma bunch is injected into the trap is measured using a Rogowski coil. The interaction of this current with the magnetic field of the trap results in the appearance of the Ampère forces confining the plasma. The plasma temperature in the trap can be determined from the measured value of the diamagnetic current. It is shown that it is possible to design a laboratory prototype of a trap with two levitating coils. The magnetic field and ion temperature in such a trap are estimated to be 0.37 T and >300 eV, respectively.

The Hall thruster exhibits two types of large-scale coherent structures: axially propagating breathing mode (m = 0) and azimuthal, with low m, typically m = 1, spoke mode. In our previous work, it was demonstrated that axial breathing mode can be controlled via the external modulations of the anode potential. Two regimes of the thruster response, linear and nonlinear, have been revealed depending on the modulation amplitude. In this work, using the high-speed camera images and developed image-processing technique, we have investigated the response of the azimuthal mode to the external modulations. We have found that, in linear regime, at low modulation voltages, axial and azimuthal structures coexist. At larger amplitudes, in the nonlinear regime, the azimuthal mode is suppressed, and only axial driven mode remains.

Injection of high-speed plasma flows into a region with a magnetic field created by a current-carrying ring conductor is considered. Analysis is performed on the basis of MHD equations expressed through the vector potential of the magnetic field with allowance for the electric conductivity, thermal conductivity, and radiation transport. The results of numerical experiments demonstrate the possibility of using plasma accelerators as injectors for magnetic confinement devices.

The paper gives examples of orbital maneuver execution of spacecraft (SC) using orbit correction propulsion system (OCPS) based on electric propulsion (EP). The high velocity of the propellant flow achieved in EP allows for orbital maneuvers with significantly lower propellant flow rate than in conventional propulsion systems. The time required to perform the orbital maneuvers using EP is connected with the available on-board power. It is typically much greater than such time needed for conventional jet propulsions. The advantages of EP are realized if mission allows a long-time operation of the propulsion system. Since the early 1970s stationary plasma thrusters (SPTs) developed on the base on the concept proposed by A.I. Morozov are used on the SC Meteor. With the help of OCPS based on SPT EOL-1, SC Meteor was installed on the conventionally synchronous orbit, which provides a fixed grid of tracks with a period of T = 102.31 min. In this case, a complete overview of all daily Earth’s surface with the bandwidth of 2900 km is obtained. In recent decades, there has been a steady trend toward miniaturization of space equipment, which requires the development of acceptable thrusters to meet new requirements. Typical total impulses of thrust required for OCPS are reduced several times. At present, a number of space constellations are being developed in Russia based on small SC with a mass from 60 to 500 kg. VNIIEM Corporation creates a space constellation IONOZOND, designed to monitor the geophysical conditions. The description of the IONOZOND constellation is given and the options for using of various OCPS, in particular, based on SPT, ion and pulsed plasma thrusters are considered. It is shown that their use in small SC can significantly increase the economic efficiency of remote sensing orbital constellations.

Results of many-year-long studies of high-power quasi-stationary acceleration and compression systems whose channel is a magnetoplasma analogue of the Laval nozzle are summarized. Double-stage quasi-stationary plasma accelerators with channels made of rod electrodes or complicated magnetoplasma transformers are described. Results are presented from experimental studies of acceleration and compression systems. It is shown that, in the optimal operating regime corresponding to the proper choice of the initial and boundary conditions, plasmadynamic devices are able to generate plasma streams with parameters close to the theoretical limit for given experimental conditions. A unique set of parameters of the generated streams were achieved: the density of the accelerated stream of up to 10¹⁶ cm^–3 at a maximum velocity of (4–4.2) × 10⁷ cm/s and the density of the compressed stream of up to 10¹⁹ cm^–3 at a plasma temperature of 60–100 eV. The total energy content in the accelerated plasma streams reaches 0.9–0.95 MJ at an accelerating channel efficiency of 0.8–0.9. The generation time of accelerated stream amounts to 150–200 particle flight times along the channel of the plasmadynamic device, while the lifetime of the compression region reaches 20–30 particle flight times.