Plasma Physics Reports最新文献

A set of magnetic coils used to correct the error fields at the Globus-M2 spherical tokamak, which appear due to the imperfections of the production and assembly of the tokamak magnetic system, is described. The magnetic sensors that are used to monitor the locked helical MHD modes are also described. The results of experiments on detecting the locked modes in the discharges with plasma heating by neutral beam injection are presented. A correlation is found between the appearance of the locked modes accompanied by the loss of fast ions and the confinement of the main plasma.

It is assumed that the low-frequency noise recorded on the surface of Mars may be associated with a charged dust component in its atmosphere and the occurrence of sound perturbations in such a dust system that modulate the electromagnetic wave from the Sun. It is also shown that it can be associated with plasma-dust processes in meteoroid tails. The mechanism for the excitation of modulational instability of an electromagnetic wave associated with a dust acoustic mode in the Martian atmosphere, namely in dust clouds at an altitude of 60 and 100 km, where the dusty plasma with particles of frozen carbon dioxide is detected, is described. It is shown that the development of modulational instability is due to the influence of high-frequency electromagnetic waves on the dusty plasma in the Martian atmosphere from both natural sources (solar radiation, lightning discharges) and anthropogenic nature (from equipment from space satellites and from stations on the surface of the planet). The parameters of electromagnetic pump waves, at which the active development of modulational instability of electromagnetic waves associated with the dust acoustic mode is expected, and the modulational instability growth rates are found. The development of the modulational instability in the dusty plasma of Martian clouds, in turn, can explain the occurrence of low-frequency noise recorded by equipment on the surface of Mars. The relation between observed radio noise in the range of 3 Hz–3 kHz and plasma-dust processes in the Martian atmosphere, in particular, in dust clouds at 60 and 100 km, as well as in dusty plasma meteroid tails, where the dust concentration is high, is discussed.

The initiation of a positive corona discharge near a model hydrometeor in air is studied numerically. Hydrometeors in the form of an ellipsoid of revolution and a cylinder with two hemispheres at the ends are considered as models. Threshold characteristics (external electric field strength, particle charge) are obtained for hydrometers of various sizes and shapes at an atmospheric pressure of 0.4−1 atm. Analysis of the results of numerous calculation options shows that the threshold field strength at the top of the hydrometeor is determined by the curvature radius of the surface at this point and air pressure. A universal dependence of the reduced threshold field strength on the product of the curvature radius of the surface and air pressure is obtained. The simulation results indicate the possibility of initiating a corona discharge in a thundercloud from the top of a hydrometeor less than a centimeter long at a subthreshold reduced field strength of 10−15 kV∕(cm atm).

In experiments with neutral beam injection on the Globus-M2 spherical tokamak, sequences of long-lasting harmonics of toroidal Alfvén modes were discovered, equidistant from each other in frequency and shifted from zero by a constant value. Using microwave Doppler backscattering diagnostics, the central localization of toroidal modes was determined. In this work, the possibility of “splitting” of toroidal harmonics due to the Doppler shift caused by the toroidal rotation of the plasma is being discussed. It is found that the unshifted frequency of the toroidal Alfvén mode obtained from the spectrum of the magnetic probe signal is in good agreement with the frequency of the mode calculated at the mode location radius, and the toroidal rotation frequency, also determined from the spectrum of the magnetic probe signal, correlates well with the rotation frequency measured using charge exchange spectroscopy diagnostics, but differs by a constant amount. Possible reasons for the discrepancies are being discussed.

We propose a 0-D model describing processes in a system comprising an atmospheric pressure DC discharge and aqueous nickel nitrate solution. The model is represented as two coupled subsystems: plasma and solution. Characteristics of the discharge plasma have been determined by jointly solving the Boltzmann equation for electrons; equations of vibrational kinetics for the ground states of N₂, O₂, NO, H₂, and H₂O molecules; and equations of chemical kinetics (328 reactions, 34 components). In doing so, use was made of experimentally determined reduced electric field strength and vibrational and gas temperatures. The kinetics of the processes in the solution included 121 reactions and 34 components. The calculation results agree with experimental data on the vibrational temperatures of N₂(X) molecules, the kinetics of the decrease in Ni²⁺ concentration, and the variation in solution pH. We have determined the degree of Ni²⁺ conversion and the energy yield of conversion and identified the mechanisms that determine the concentration of the major solution components.

The results of preliminary experiments on measuring the spatial asymmetry of plasma flows in the GOL-NB device using movable Mach probe are presented and the diagnostics used is described. In the experiments, the high-field sections were mounted in the configuration with solenoidal magnetic field. The dynamics of plasma flows was recorded which was expected in the trap: the plasma flowed from the plasma gun along the magnetic field, accumulated in the GOL-NB central trap, and then after the plasma gun was switched off, flowed out from the central trap in two directions. At time of transition from the stage of plasma accumulation to the stage of its decay, the direction of plasma flow in the input high-field section was inverted. The balance of particles in the central trap is discussed. Experiments have shown that this technique can be used for studying the effects of improving plasma confinement after switching to the multiple-mirror configuration of high-field sections, in which, according to theory, under optimal conditions, a flow of b-ackscattered particles should arise, which will return them from the multiple-mirror sections to the confinement zone.

The results of studying instabilities in flat aluminum 4-μm-thick foils exploded using the GVP generator with a short circuit current of 10 kA and a current rise time of 350 ns are presented. The dynamics of foil destruction during the explosion was studied using laser probing. During the experiments, it was ascertained that in the presence of the two-dimensional structure of foil, the growth rates of instabilities and their nature depend on the foil orientation relative to the direction of current flow. The conditions are cleared up, under which during the explosion of foils with two-dimensional inherent structures, the development of instabilities is slowed down.

The results of research on the creation of a powerful source of soft X-ray radiation (SXR, hν > 100 eV) based on the Z-pinch of compact nested arrays are presented. One of the applications of such an SXR source can be radiation ablation of targets made of various substances in experiments on high-energy density physics and extreme states of matter, which are currently being actively carried out worldwide. Experiments are carried out on plasma implosion of combined nested arrays with different ratios of array radii at a discharge current level of up to 3.5 MA at the pulse power facility Angara-5-1. The outer array consisted of fibers of a substance with a low atomic number (polypropylene) and the inner array consisted of a substance with a high atomic number (tungsten). It is shown that in the case of nested arrays of this design, it is possible to obtain a significant (~1.4 times) increase in the peak SXR power compared to single W arrays with the same parameters as the W array in the inner array. At the same time, spectral data obtained using a “flat field” grazing incidence spectrograph demonstrate a significant decrease in the fraction of tungsten ions in the trailing plasma around the pinch of nested arrays. By optimizing the linear mass of the outer array and its radius, powerful and short SXR pulses with amplitude of ~10 TW, energy of ~130 kJ and duration of ~4–5 ns are obtained. This made it possible to increase the incident power density and fluence on the target up to 1.55 TW/cm² and 17 kJ/cm², respectively, in experiments on extreme states of matter currently being carried out at the facility.

The method for determining the absolute plasma density in sources that create plasma in the strong magnetic field using the electron beam has been developed and tested. The results of plasma density measurements in the source of tubular plasma used in research on plasma relativistic microwave electronics are presented. It was shown that at time of switching-on plasma maser, for discharge currents of 5, 9, and 20 A, the plasma densities were (3 ± 0.3) × 10¹², (5.5 ± 0.6) × 10¹², and (9.5 ± 1) × 10¹² cm^–3, respectively. Comparison with the probe measurements previously performed, as well as with the numerical calculations made using the KARAT code, showed good agreement between the results of microwave measurements and numerical calculations, while the measurement error did not exceed 15%. The results of probe measurements much stronger deviate from the results of microwave measurements, which is associated with the presence of the strong magnetic field in the plasma source.

The propagation of electron-acoustic waves in a collisionless unmagnetized plasma composed of hot electrons obeying the Cairns–Gurevich (CG) distribution, inertial cold electrons and stationary ions are considered. The basic field equations of the above described plasma is re-examined through the use of the modified Poincare–Lighthill–Kuo (PLK) method. Introducing the strained coordinates and expanding the field quantities into the parameter (epsilon ), a set of differential equations is obtained. The lowest order term in the perturbation expansion is governed by the modified KdV equation, whereas the second order term is governed by the modified linearized KdV equation with nonhomogeneous term. Then, studying the localized travelling wave solution for the evolution equations, the strained coordinates for this order is determined so as to remove the possible secularities that might occur in the solution. It is observed that the ratio of the second order term to the first order term in the perturbation expansion is negative and not so small. This is equivalent to saying that the contribution of second order term decreases the wave amplitude. In other words, retaining only the first order term in the perturbation expansion overestimates the real value of the field quantities.