P. V. Silin

Study of a cumulative jet in a plasma focus discharge by the method of shearing interferometry

The dynamics of the cumulative jet formed in the course of plasma compression in a plasma focus discharge is investigated by the method of differential optical interferometry. The jet propagation velocity is found to be V = (2.3–3) × 107 cm/s, which coincides with the results of calculations performed in a 2D ideal MHD model. Ejection of matter from the anode in the late stage of the discharge due to the interaction of the cumulative jet and the electron beam with the anode surface is observed.

Laser-optical measurements of the velocities of the plasma jets formed from different gases in a kilojoule-range plasma focus facility

The velocities of the plasma jets formed from Ne, N2, Ar, and Xe gases in plasma focus facilities were determined by means of laser-optical shadowgraphy of the shock waves generated at the jet leading edge. In spite of the almost tenfold ratio between the atomic weights of these gases, the outflow velocities of the plasma jets formed in experiments with these gases differ by less than twice, in the range of (0.7–1.1) × 107 cm/s under similar discharge conditions. The energies of the jet ions were found to vary from 0.7 keV for nitrogen to 4 keV for xenon.

Influence of conditions of shock-wave effect of plasma on the structure and current-carrying capacity of multilayer high-temperature superconducting tapes

The article presents the results of the investigation of the influence of shock-wave effects on the structure and the critical currents of multilayer high-temperature superconductors—HTS tapes produced by the EAS-E HTS (VAC). Shock-wave exposure was carried out using an installation of a plasma focus (PF) type. It was experimentally found that an increase in the critical current by 20% or more was achieved in its own magnetic field and in external magnetic fields in the range of 0.5–2.5 T. The increase depended on the conditions of the shock-wave treatment (the distance from the plasma source (PF anode) and the number of shock wave pulses). In magnetic fields of more than 3 T, the effect of an increase in the critical current was not observed. Microstructural studies revealed both a compression and destruction of the individual layers of HTS in the strike zone depending on the conditions of the impact. The most severe degradation of the structure and the critical current was shown on the tape samples treated at distances of 25–30 mm from the PF anode. The critical current increased and exceeded the initial values of untreated tapes (75–85 A) at distances of 35–65 mm. The phase composition of HTS layers by XRD changed little after shock-wave treatment. Depending on the number of shock pulses and distance from the anode in the area of treatment, the tape’s thickness was reduced owing to compression or was increased owing to swelling of the tape.

Study of deuterium and hydrogen distributions in Ta|CD2|Ta, Ta|Ta|CD2|Ta|Ta, and Nb|CD2|Nb assemblies after exposure to high-temperature argon plasma

Assemblies made of Ta|CD2|Ta, Ta|Ta|CD2|Ta|Ta and Nb|CD2|Nb foils are irradiated with pulses of high-temperature argon plasma created by means of a “Plasma Focus” setup. The irradiated foil samples are investigated by recording the recoil nuclei of hydrogen and deuterium. It is found that hydrogen and deuterium are redistributed in foil stacks. The ultradeep penetration of light gas impurities (hydrogen and deuterium) can be explained by the influence of shock waves on the foils and accelerated diffusion under an external force.

Dynamics of axial plasma jets in neon and argon plasma focus discharges

Axial plasma jets at the final stage of plasma focus discharge filled by neon or argon were studied by the method of shearing interferometry. It was found that neon plasma is more stable than argon one and jets in neon are stronger than in argon. The velocity of current sheath, taken from experiment, is Vsh = (2-3) × 106 cm/s, while the velocity of cumulative jet is Vj = (3-4) × 107 cm/s. These features are supported by theoretical interpretation given in the frame of 2D MHD model.

Effect of Pulsed Nitrogen Plasma and Nitrogen Ion Fluxes on the Structure and Mechanical Properties of Vanadium

The effect of powerful pulsed fluxes of nitrogen plasma and nitrogen ions generated in the PF-4 Plasma Focus setup (LPI; energy flux density of plasma pulse was 108–1010 W/cm2) on the modification of vanadium surface is studied. Melting and ultrafast solidification result in a fine cellular structure (cell size of 100–200 nm) in a thin surface layer in samples. There are irradiation regimes causing directional crack growth after solidification and cooling of the surface layer and the formation of a block microstructure with a block size of several tens of micrometers. The thickness of the melted layer in the samples is 2–4 μm. Cracks propagate to a depth of 5–20 μm. It is established that irradiation by pulsed nitrogen plasma and high-energy nitrogen ions changes the microhardness of the vanadium surface layers. The microhardness increases by a factor of three with the number of plasma pulses and the distance between a sample and the anode of the Plasma Focus (PF) setup. The increase in the microhardness is in agreement with the refinement of coherent scattering regions, the increase in lattice microstrain ε, and the formation of vanadium nitrides. Pulsed fluxes of nitrogen plasma and nitrogen ions decrease the lattice parameter much greater than cold working (rolling) does. The lattice parameter decreases when the total irradiation power is increased (the number of pulses increases or the distance between a sample and the anode of the PF setup decreases). Such changes seem to be caused by the action of the residual macrostresses induced by pulsed plasma irradiation. In addition, X-ray diffraction analysis showed a change in the texture of the surface layer after ion-plasma treatment of coldworked vanadium samples in the PF setup.

Distribution of deuterium and hydrogen in Zr and Ti foil assemblies under the action of a pulsed deuterium high-temperature plasma

Deuteron and proton elastic recoil detection analysis is used to study the accumulation and redistribution of deuterium and hydrogen in assemblies of two high-pure zirconium or titanium foils upon pulsed action of high-temperature deuterium plasma (PHTDP) in a plasma-focus installation PF-4. It is noted that, under the action of PHTDP, an implanted deuterium and hydrogen gas impurity are redistributed in the irradiated foils in large depths, which are significantly larger than the deuterium ion free paths (at their maximum velocity to ~108 cm/s). The observed phenomenon is attributed to the carrying out of implanted deuterium and hydrogen under the action of powerful shock waves formed in the metallic foils under the action of PHTDP and/or the acceleration of diffusion of deuterium and hydrogen atoms under the action of a compression–rarefaction shock wave at the shock wave front with the redistribution of deuterium and hydrogen to large depths.

Studying the Generation Stage of a Plasma Jet in a Plasma Focus Discharge

A dense compact plasmoid generated at the pinch collapse stage is revealed in a plasma focus discharge by laser optical methods. The initial size of the plasmoid is ~1 mm, its electron density is more than 2 × 1019 cm–3, and the plasmoid propagates along the axis from the anode at an average velocity of more than 107 cm/s. A shock wave is generated in the residual argon plasma during the motion of the bunch, its density decreases to 1018 cm–3 at a distance of 3 cm from its place of generation, and the plasmoid expands by 3–5 times and almost merges together with the leading edge of the shock wave.

Observation of the ionization wave and the shock wave ahead of the plasma jet generated in the plasma focus discharge

An ionization wave travelling ahead of the shock wave of the plasma jet, propagating in residual gas (nitrogen) of the plasma focus discharge, is detected by the laser-interferometry method at the plasma focus. Radial and axial distributions of electron densities of the shock wave and plasma jet are measured.

Hydrogen and deuterium distribution in tungsten foils irradiated with high-temperature deuterium plasma in H2O- or D2O-filled hermetic chambers

Processes of deuterium and hydrogen accumulation and redistribution are studied via the elastic recoil detection method with the help of a Plasma Focus (PF-4) setup. These processes proceed when high-temperature pulsed deuterium plasma acts on two external tungsten foils used as the main elements of hermetic chambers filled with distilled or heavy water and one internal tungsten foil inserted into an aqueous medium. It is established that, under the action of pulsed deuterium plasma on the heavy water-filled chamber, implanted deuterium atoms and those existing in the heavy water, as well as hydrogen contained in the tungsten foils, are redistributed over the entire thicknesses of the three foils. When the distilled water-filled chamber is irradiated with pulsed deuterium plasma, implanted hydrogen is observed across the whole thickness of the external tungsten foils with a depth distribution maximum. Hydrogen and deuterium reach their maxima on the foil surface immersed in liquid. The revealed phenomenon can be explained by the fact that chemical bonds in the heavy and distilled water are broken and, afterward, free hydrogen and deuterium atoms are transferred to tungsten foils under the action of intense shock waves excited in the chamber.