G. V. Ostrovskaya

Experimental study of plasma compression into the sheet in three-dimensional magnetic fields with singular X lines

The formation and evolution of the plasma sheets resulting from the plasma compression in diversified three-dimensional (3D) magnetic configurations with singular X lines are reported on. The research was focused on the correlation between the structure of a plasma sheet and the topology of the initial 3D magnetic configuration, especially on the impact of the guide field aligned with the X line. It has been demonstrated experimentally that plasma compression and formation of extended plasma sheets can take place in configurations with the X lines in the presence of a strong guide field. The electron density distributions in the plasma sheets were found to be rather sensitive to the magnetic field topology. The experiments revealed the effect of progressive decrease of the plasma compression ratio in response to increasing guide field. This effect has two basic manifestations: a decrease of the maximum plasma density and an enlargement of the sheet thickness. Based on the experimental data we advanced a c...

Spectroscopic Measurements of the Electron and Ion Temperatures and Effective Ion Charge in Current Sheets Formed in Two- and Three-Dimensional Magnetic Configurations

The spatial distributions of the electron temperature and density, the effective and average ion charges, and the thermal and directed ion velocities in current sheets formed in two-dimensional magnetic fields and three-dimensional magnetic configurations with an X line were studied using spectroscopic and interference holographic methods. The main attention was paid to studying the time evolution of the intensities of spectral lines of the working-gas (argon) and impurity ions under different conditions. Using these data, the electron temperature was calculated with the help of an original mathematical code based on a collisional-radiative plasma model incorporating the processes of ionization and excitation, as well as MHD plasma flows generated in the stage of the current-sheet formation. It is shown that the electron temperature depends on the longitudinal magnetic field, whereas the ion temperature is independent of it. The effective ion charge of the current-sheet plasma was determined for the first time.

Study of the structure and dynamics of current sheets in three-dimensional magnetic configurations with an X line by holographic interferometry

Results are presented from studies of the structure and dynamics of current sheets in three-dimensional magnetic configurations with an X line by means of holographic interferometry. It is found that the efficiency of plasma compression into the sheet is reduced as the longitudinal magnetic field Bz, directed along the X line, increases. This effect is attributed to the enhancement of the longitudinal component of the magnetic field within the sheet and to the corresponding increase in the magnetic pressure. It is shown that the formation of a plasma sheet lags behind the beginning of the plasma current pulse, the delay time being close to the characteristic Alfvén time.

Holographic interferometry study of two-fluid properties of the plasma in current sheets formed in heavy noble gases

Two-exposure holographic interferometry was used to study the structure of current sheets formed in three-dimensional magnetic configurations with a singular X line in heavy noble gases (Ar, Kr, and Xe). It is found that, in the presence of a longitudinal magnetic field BZ directed along the X line, plasma sheets take on an unusual shape: they are titled and asymmetric. Their asymmetry becomes more pronounced as the mass of a plasma ion increases—a manifestation of the two-fluid properties of the plasma. The observed effects can be attributed to additional forces arising due to the interaction of the longitudinal magnetic field BZ with Hall currents excited in a plane perpendicular to the X line. A qualitative model describing plasma dynamics with allowance for the Hall effect and accounting for most of the experimentally observed effects is proposed.

Study of Current Sheets in Three-Dimensional Magnetic Fields with an X-Line by Holographic Interferometry

Results are presented from experimental studies of the spatial electron density distribution in current sheets formed in three-dimensional magnetic configurations with X-lines. The electron density is measured by using two-exposure holographic interferometry. It is shown that plasma sheets can form in a magnetic configuration with an X-line in the presence of a sufficiently strong longitudinal magnetic-field component B∥ when the electric current is excited along the X-line. As the longitudinal magnetic-field component increases, the electron density decreases and the plasma sheet thickness increases; i.e., the plasma is compressed into a sheet less efficiently.

Effect of the initial plasma parameters on the structure of the current sheets developing in two-dimensional magnetic fields with a null line

The effect of the initial plasma parameters on the structure of the plasma of the current sheets that form in two-dimensional magnetic fields with a null line is studied by holographic interferometry. The evolution of the plasma sheets that develop in an initial low-density plasma, where a gas is mainly ionized by a pulse current passing through the plasma and initiating the formation of a current sheet, has been comprehensively studied for the first time. At the early stage of evolution, the spatial structure of such a plasma sheet differs substantially from the classic current sheets forming in a dense plasma. Nevertheless, extended plasma sheets with similar parameters form eventually irrespective of the initial plasma density.

Plasma dynamics inside the current sheet

Plasma dynamics is investigated by the five-frames holographic interferometry and the Doppler broadening of spectral lines. The explosive stage of magnetic reconnection is accompanied by plasma sheet destruction and the appearance of high velocity plasma flows.

Holographic Diagnostics of the Plasma: A Review

A review of works concerning holographic diagnostics of the plasma that have been conducted in the laboratory of plasma optics at the Ioffe Physico-Technical Institute since 1966 is presented. The potential and features of holographic diagnostics as applied to different plasma objects are discussed. The results of investigations into the laser-induced spark in gases and current sheets forming in 2D and 3D magnetic fields with X lines are reported.

Repetitive torch in a coaxial waveguide: Temperature of the neutral component

The temperature of the neutral component in a repetitive microwave torch excited in an argon jet injected into atmospheric air is measured using different optical methods. The microwave energy is efficiently converted into the thermal energy of the argon jet. The gas temperature is maximum at the nozzle, where it reaches 4.5–5.0 kK, and decreases to 2.5–3.0 kK along the jet. The torch plasma, which is not in thermal equilibrium, drastically influences the working gas and the surrounding air.

Efficiency of optical-to-acoustic energy conversion upon the interaction of a pulsed laser radiation with a liquid: I. Calculation of the efficiency upon acoustooptic interaction

Relationships for the efficiency of conversion of laser radiation energy to acoustic energy for the acoustooptic (thermal) mechanism of interaction are derived. The cases of short and long laser pulses interacting with the rigid and free boundaries of a heavily absorbing liquid are considered. The efficiency is numerically calculated for the situation when the radiation of a transverse-excitation atmospheric (TEA) CO2 laser interacts with water with regard for the temperature variation of the volume thermal expansion coefficient of the latter.