Galina V. Dreiden

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...

Splitting induced generation of soliton trains in layered waveguides

We report first experimental registration of the splitting induced generation of a soliton train from a single incident strain soliton in two- and three-layered elastic waveguides. The origin is in the nonlinear response of the wave to an abrupt change of physical properties of the waveguide. We show a good agreement between our experimental results and theoretical estimates, based on a weakly nonlinear solution for the doubly dispersive (Boussinesq type) equation with piecewise constant coefficients for the waveguide made of a piecewise isotropic nonlinearly elastic material.

Dynamics of laser‐driven shock waves in water

Shock waves were produced in water by directing unfocused 0.4‐J, 20‐ns ruby (λ=0.693 μm) or 3‐J, 8‐ns Nd‐glass (λ=1.06 μm) laser light onto the metalized surface of a thin plastic foil. The illuminated areas were 0.35 and 2.3 cm2, respectively, corresponding to laser irradiances of 52.6 and 68.4 MW cm−2. The radial propagation velocity and the profile of the generated waves have been measured via double‐exposure interferometric holography and shadowgraphy. Using the obtained values of the shock velocities and the fringe shift in the interferograms, the pressure on the shock wave front, the thickness of the compressed water layer, the laser energy consumed in producing this layer, and the time required for its formation have been calculated.

Comparison of the effect of cyanoacrylate- and polyurethane-based adhesives on a longitudinal strain solitary wave in layered polymethylmethacrylate waveguides

We study the effect of two types of adhesive bonding on the propagation of a localized longitudinal strain wave in two- and three-layered elastic bars. The detectable variation in the decay rate of the wave at relatively long distances of propagation is observed. It is proposed that such variation can be used as an indicator of the type of an interface.

Bulk strain solitary waves in bonded layered polymeric bars with delamination

We report the registration of delamination induced variations in the dynamics of bulk strain solitary waves in layered polymeric bars with the glassy and rubber-like adhesives, for the layers made of the same material. The key phenomenon in a layered structure with the glassy bonding is the delamination caused fission of a single incident soliton into a wave train of solitons, with the detectable increase in the amplitude of the leading solitary wave. The significant feature of bulk strain solitons in structures bonded with the rubber-like adhesive is the generation of radiating solitary waves, whilst co-propagating ripples disappear in the delaminated area. The observed variations may be used for the detection of delamination in lengthy layered structures.

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.

Evolution of bulk strain solitons in long polymeric waveguides

We have studied the propagation of longitudinal strain solitons in waveguides made of polystyrene and plexiglas (polymethyl methacrylate) and long enough to provide noticeable changes in the wave shape and amplitude. The decay rate for nonlinear waves in these materials is estimated from the experimental data. An anomalously weak attenuation of strain solitons in polymers featuring a high dissipation of linear waves is discovered for the first time.

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.

Observation of bulk strain solitons in layered bars of different materials

It is shown that the behavior of a bulk strain soliton in layered waveguides, comprising layers of different materials, depends on the type of contact between layers. In delaminated waveguides, solitons propagate independently in each layer and possess significantly different velocities and amplitudes that depend on the parameters of layer materials, whereas a single resultant soliton propagates in a waveguide bonded with a glassy adhesive. These properties of nonlinear bulk strain waves can be used for nondestructive testing due to the negligibly small damping of bulk solitons.