V. I. Krauz

The formation of the micropinch structure in plasma focus by the addition of heavy impurities

The results of an experimental study of the formation of micropinches (MP) in a plasma focus discharge in the presence of small impurities of heavy gas are reported. MPS of 10-100 mu m in size are observed and the X-ray spectra of multicharged ions of the impurity (Xe) are registered.

Magnetic probe measurements of the current sheath on the PF-3 facility

Results are presented from experimental studies of the dynamics of the current sheath (CS) on the PF-3 plasma focus facility. The parameters of the sheath, including the current distribution in it, were measured using absolutely calibrated magnetic probes installed at different positions with respect to the facility axis and the anode surface. The CS dynamics in discharges operating in argon and neon was investigated, and the skin depth in different stages of the discharge was determined. One of the probes was installed at a distance of ≈2 cm from the facility axis, which made it possible to estimate the efficiency of current transfer to the region of pinch formation. Operating modes were obtained in which the current dynamics detected by magnetic probes at different distances from the axis agreed well with the dynamics of the total discharge current until the instant of singularity in the current time derivative. It is shown that shunting breakdowns can lead to the formation of closed current loops. The shunting of the discharge current by the residual plasma is directly related to the efficiency of snowplowing of the working gas by the CS as it propagates from the insulator toward the facility axis.

Dynamics of the structure of the plasma current sheath in a plasma focus discharge

The study is aimed at investigating the fine structure of the plasma current sheath (PCS) in the PF-3 plasma focus facility. The PCS dynamics in a deuterium discharge was studied. The PCS parameters were measured using absolutely calibrated magnetic probes installed at different positions with respect to the facility axis and the anode surface. A magneto-optical probe recording both the magnetic signal and the PCS optical luminosity was first applied to analyze the PCS structure. This made it possible to spatially resolve the current and shock-wave regions. It is demonstrated that the current distribution is different in different discharge stages. It is shown that the neutron yield is determined by the value of the current compressed toward the axis, rather then the amplitude of the total discharge current.

Laboratory and computer simulations of super-Alfvénic shocks in a weakly ionized medium

High Mach number shocks have been studied experimentally at the Kurchatov Institute in 2000 with the PF3 Plasma Focus [N. V. Filippov et al., Phys. Lett. A 211, 168 (1996)]. The main goal of these especially designed laboratory experiments was to provide data against which to test current numerical models, in order to better understand the interaction of a high-velocity plasma jet with a partially ionized gas in a strong transversal magnetic field. Observed magnetic field compression, plasma density profile evolution, and shock slowing down, are well reproduced by a two-dimensional hybrid code HAWAI2D [B. Lembege and F. Simonet, Phys. Plasmas 8, 3967 (2001)] with Monte Carlo collisions. Some of the code initial conditions are directly obtained from the numerous diagnostics installed in the experimental chamber. Others are derived from jet velocity and background density measurements, making use of a simplified model of jet propagation from the pinch. Ion-neutral collisions play a central role in the shock...

Experimental simulation of the collisionless shock wave by Plasma Focus

The aim of this study is to reproduce a superalfvenic collisionless shock wave by using the Plasma Focus Facility as a plasma source. The experiments were performed on PF-3 Facility (Plasma Focus Filippov-type) at the level of energy supply up to 1 MJ. At compression of a current-plasma sheet to an axis in the stage of a plasma focus formation, the generation of cumulative plasma jets driven along the axis with a velocity ≈ 107 cm/s takes place. This directed driving is realized in the ambient plasma arisen as a result of the working gas ionization by the X-ray radiation of the plasma focus. The transversal magnetic field up to 2500 G was created by the magnetic system based on rare-earth magnets. The experimental conditions allowed us to perform experiments with Alfvén Mach numberMA>-3.

Spectroscopic measurements of the parameters of the helium plasma jets generated in the plasma focus discharge at the PF-3 facility

The spectroscopic technique used to measure the parameters of the plasma jets generated in the plasma focus discharge and those of the plasma of the immobile gas through which these jets propagate is described. The time evolution of the intensities and shapes of spectral lines in experiments carried out with helium at the PF-3 facility was studied by means of electron-optical streak cameras. The plasma electron temperature, T ≈ 4–5 eV, was determined from the intensity ratio of two spectral lines, one of which (λ1 = 5876 Å) belongs to neutral helium, while the other (λ2 = 4686 Å), to hydrogen-like helium ions. The plasma density at different time instants was determined from the Stark broadening of these lines in the electric fields of different nature. The plasma density is found to vary from 4 × 1014 to 2 × 1017 cm−3.

Influence of the radiation of the plasma-focus current sheath on the implosion dynamics of condensed targets

Results are presented from experimental and theoretical studies of the influence of the radiation of the plasma-focus current sheath on the implosion dynamics of condensed targets. Radiative losses from the current sheath of a plasma focus in neon, argon, and hydrogen with a 2% admixture of Xe are calculated with allowance for the line, bremsstrahlung, and recombination radiation. It is shown that the temperature of the neon plasma (10–15 eV) is quite sufficient to evaporate Al2O3 grains of radii 10–20 μm. The use of neon as a working gas makes it possible to alter the cold-start condition in experiments on the implosion of foam liners.

Study of the dynamics of a plasma current sheath in the KPF-4 Phoenix plasma-focus facility

The engineering characteristics of the KPF-4 Phoenix megajoule Mather-type plasma focus facility constructed at the Sukhumi Physicotechnical Institute are described. Results from preliminary studies of the plasma dynamics at a capacitive-storage energy of up to 700 kJ are discussed. Future experiments in KPF-4 will be oriented at technological applications and will complement the studies carried out in the 2.8-MJ Filippovtype PF-3 plasma focus facility at the Nuclear Fusion Institute of the Russian Research Centre Kurchatov Institute.

Properties of the distribution of azimuthal magnetic field in a plasma flow during laboratory simulations of astrophysical jets in a plasma-focus installation

The results of laboratory simulations of astrophysical jets are presented. Plasma flows generated in the PF-3 plasma-focus installation of the NRC “Kurchatov Institute” and propagating to distances substantially exceeding their transverse dimensions are studied. It is shown usingmagnetic probes that the plasma flow propagates with a frozen-in magnetic field. The resulting radial distribution of the azimuthal magnetic field corresponds well to the distribution created by a longitudinal current of ~10 kA flowing in a region with a radius of 1–2 cm near the axis. Structures associated with return currents are observed at the periphery of the flow. The magnetic field decays rapidly as the flow propagates along the axis. Nevertheless, the leading lobe of the plasma flow is preserved to substantial distances in a neon discharge, possibly due to radiative cooling of the plasma.

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.