Vol 50, No 7 (2024)

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.

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 backscattered 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 paper describes a method for generating aluminum and hydrogen plasma jets. It illustrates the formation mechanism of extended plasma structures produced during the combustion of a high-current vacuum-arc discharge. The current-carrying plasma front is shown to propagate at different velocities for aluminum plasma and hydrogen plasma. The hydrogen plasma has a substantially higher initial velocity (about 30 cm/μs) compared to the aluminum plasma (about 10 cm/μs). It is shown that the bulk velocity of the hydrogen plasma jet is about 9 cm/μs. It was proven by means of spectral diagnostics that the hydrogen plasma jet is indeed composed mainly of hydrogen.

The radiation field of a multi-dimensional plasma formation can be substantially asymmetrical. Often, the luminosity of such an object is determined using one-dimensional models with various correction factors to account for the nonsphericity. In this work, a model is presented for the determination of the luminosity of asymmetrical plasma formations based on consistent multi-dimensional radiation–hydrodynamics calculation on the example of the scenarios of supernovae with an equatorial disk. The simulations were compared with the observations of the supernova SN2009ip. The bolometric light curves were determined for the observation of this object in the disk plane and from the pole. A conclusion was made that it is impossible to describe the multi-dimensional structure of the radiation field within the framework of the one-dimensional model with correction factors and that, rather, a full three-dimensional simulation is required.

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 plasmadust 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).