Yu. V. Vinogradova

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.

Magnetic field distribution in the plasma flow generated by a plasma focus discharge

The magnetic field in the plasma jet propagating from the plasma pinch region along the axis of the chamber in a megajoule PF-3 plasma focus facility is studied. The dynamics of plasma with a trapped magnetic flow is analyzed. The spatial sizes of the plasma jet region in which the magnetic field concentrates are determined in the radial and axial directions. The magnetic field configuration in the plasma jet is investigated: the radial distribution of the azimuthal component of the magnetic field inside the jet is determined. It is shown that the magnetic induction vector at a given point in space can change its direction during the plasma flight. Conclusions regarding the symmetry of the plasma flow propagation relative to the chamber axis are drawn.

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.

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 soft X-ray emission during wire array implosion under plasma focus conditions at the PF-3 facility

Results of measurements of soft X-ray emission with photon energies of <1 keV under conditions of a plasma focus (PF) experiment are presented. The experiments were carried out at the world’s largest PF device—the PF-3 Filippov-type facility (I ⩽ 3 MA, T/4 ≈ 15–20 µs, W0 ⩽ 3 MJ). X-ray emission from both a discharge in pure neon and with a tungsten wire array placed on the axis of the discharge chamber was detected. The wire array imploded under the action of the electric current intercepted from the plasma current sheath of the PF discharge in neon. The measured soft X-ray powers from a conventional PF discharge in gas and a PF discharge in the presence of a wire array were compared for the first time.

Study of the implosion of wire arrays at the PF-3 facility

Results of experiments on the compression of tungsten wire arrays by the plasma current sheath (PCS) of the PF-3 facility at currents of up to 2 MA are presented. The efficiency of current transportation to the wire array and switching-over of the discharge current to the array were studied. Information on the penetration of the magnetic field into the wire array obtained using microprobes made it possible to compare the obtained experimental data with the results of magnetic field measurements carried out at other high-power electrophysical devices. The intensity of plasma production from tungsten wires under the action of the plasma focus PCS is estimated. The experimental results are tested against the existing models of wire array implosion with prolonged plasma production.

INVESTIGATION OF THE PULSED PLASMA FLOW, GENERATED IN NON-CYLINDRICAL Z-PINCH SYSTEMS, BY ELECTRON-OPTICAL METHODS

В последнее время наблюдается значительный рост интереса к генерируемым в Z-пинчевых системах плазменным потокам. Это связано как с пониманием роли процессов, приводящих к генерации потоков, в общей физике формирования и динамики пинча, так и с все возрастающим практическим использованием этих потоков. В работе описана система щелевого электроннооптического фотографирования в видимом диапазоне, созданная для исследования динамики импульсных плазменных потоков, вызванных сжатием Z-пинча. Эксперименты проведены на установке ПФ-3, крупнейшей в мире среди представителей одной из разновидностей Z-пинчевых систем — плазменный фокус. Приведены первые результаты измерений скорости плазменных потоков при использовании различных рабочих газов (водород, неон, аргон). Показана структурированность плазменного потока. Обнаружено отсутствие существенной зависимости скорости потока от сорта рабочего газа.

Development and study of a portable plasma focus neutron source

The work is devoted to designing a compact pulsed neutron source on the basis of a plasma focus (PF) discharge. The main task was to study the physical processes accompanying a sub-kilojoule repetitive PF discharge. A device with a power supply energy of up to 600 J and pulse repetition rate of up to 10 Hz has been developed and put into operation. The dependence of the neutron yield as a function of the pulse repetition rate has been studied experimentally. A neutron flux of ∼108 neutrons/s has been obtained in the 3-s-long packet mode with a repetition rate of 10 Hz and discharge current of 80–90 kA.

Formation of nanostructures in a plasma focus discharge

A new method for creating nanostructures in a plasma focus discharge is proposed. It is shown that the material of a micron-size dust target produced at the discharge axis efficiently evaporates and is then involved in the pinching process. After the pinch decays, the plasma expands with the thermal velocity and the evaporated dust material is deposited on the collectors in the form of fractal particles or nanoclusters organized into various structures. Such structures have a well-developed surface, which is important for various technological applications.