The radial distribution of the Bz field at a distance of 35 cm from the generation region of the axial jet emission (the anode surface of the setup) has been studied using the PF-3 plasma-focus facility. The measurements have been performed using multichannel magnetic probes located in the flight chamber of the facility. This has made it possible to measure the magnetic field distribution at 18 points on both sides of the flight chamber axis. The magnetic probes have been calibrated both in absolute value and in the magnetic field direction. An external multi-turn solenoid has been used to create the initial longitudinal (poloidal) magnetic field. The solenoid power supply circuit has allowed obtaining different Bz field directions: along or against the facility axis. It is shown that the poloidal field distribution reaches its maximum in the bunch center and decreases at the periphery, regardless of the presence of an external magnetic field. The Bz field has a radial distribution Bz(r), close in shape to the magnetic field distribution of the solenoid. The work is performed within the program for the simulation of jets of young stellar objects.

The article describes the results of the development of a diagnostic complex for studying plasma dynamics. The basic operating principle of the complex is to project an image of a plasma object at the input of the device with further division of optical radiation into several channels using semitransparent mirrors. Images in each channel are recorded by a photographic system in which an image intensifier tube serves as a fast shutter. The use of the delay system allows one to observe the dynamics of the process under study in a multi-frame mode from a single angle. The complex has been tested in studies of plasma flow dynamics at the PF-3 plasma focus facility.

The use of “plasma focus” type facilities, such as PF-3 (Kurchatov Institute), allows carrying out well-controlled and diagnosable laboratory experiments to study laboratory jets with scale parameters close to the jets of young stars. In this paper, we present the results of numerical modeling of plasma outburst propagation in PF-3. A self-consistent configuration was chosen as the initial conditions, which correctly describes the internal structure of the jet. This allowed us to obtain a detailed structure of the interaction between the magnetized emission and the ambient gas. Due to the scalability of such a structure, one should expect such a structure from the head shock waves of jets of young stars.

Astrophysical jets are collimated plasma outflows observed in diverse astrophysical settings covering seven decades of spatial scale and twenty decades of power, which, nevertheless, share many common features. This similarity over wide range of scales indicates a common core of physics underlying this phenomenon, leading to considerable interest in observational, theoretical and numerical studies. Laboratory astrophysics experiments for simulating astrophysical jets are premised on this common core of physics responsible for multi-scale similarity of jets remaining valid down to laboratory spatial scales of millimeters. Jets formed after the disassembly of the non-cylindrical Z-pinch formed in a plasma focus installation have recently been subjects of observational studies. They offer an important complementarity to the main lines of investigations in two respects. Firstly, the multi-faceted role of gravity, radiation, nuclear reactions and related astrophysics is eliminated retaining only a rapid implosion of a compact plasma object in a magnetohydrodynamic environment as a common feature. Secondly, observations can be made using techniques of laboratory plasma diagnostics. In this paper, we report preliminary results regarding presence of poloidal magnetic flux associated with the jets lasting long after the pinch disassembly. This is significant in the context of uncertainty regarding the origin of poloidal magnetic field postulated in several MHD models of astrophysical jet phenomena. Evidence indicating presence of a radial component of electric field suggests existence of plasma rotation as well. These results suggest that more refined experiments can provide insights into the astrophysical jetting phenomena not available from observational astronomy techniques.

Jets from young stars are used as an example to review how laboratory modeling enables advancement in understanding the main physical processes responsible for the formation and stability of these amazing objects. The discussion focuses on the options for modeling jet emissions in a laboratory experiment at the PF-3 facility at the National Research Center Kurchatov Institute. Many properties of the flows obtained using this experimental setup are consistent with the main features of jets from young stars.

Laboratory simulation is an effective tool for studying astrophysical processes. The paper considers a scheme for simulating jets from young stellar objects by means of a plasma-focus device with application of an external poloidal magnetic field. The mechanisms of amplification of the poloidal magnetic field in the region where the plasma flow is formed by the conductive plasma sheath upon its compression toward the axis of the system up to values of ~100 kG are discussed. Magnetic probe measurements have shown that the value of the B z component of the field also increases significantly in the plasma flow itself, while the direction of the field captured by the flow corresponds to the direction of the external applied field. An increase in the toroidal component of the magnetic field is also observed. It is concluded that this experiment quite accurately simulates the processes in young stellar objects, including accretion and the operation of the “central engine.”

We present the results of laboratory simulation of jets from young stars at the PF-3 plasma focus facility at the NRC “Kurchatov Institute.” The objective of research question was to determine factors making the spatial structure of plasma jets in discharges in gases of different chemical compositions, namely, neon, helium, and helium with admixtures of neon, different. It was found that the plasma flow in the case of pure neon is the most structured: the head of the ejection consisted of numerous clumps, which makes is very similar to clumps in the jets from young stars, the so-called Herbig–Haro objects. The ejection in the case of pure helium was the least structured. However, the shape of the ejection head substantially changes upon admixing merely 1% of neon into helium, revealing a noticeable small-scale structure. Estimates show that these specific features can be related to the difference in the cooling efficiency of the studied gases both in the plasma ejection itself and in the shock wave generated upon jet propagation through the background gas. It is suggested that the main reason for the appearance of inhomogeneities in the plasma blob are different types of instabilities that develop in the presence of efficient radiative cooling, as is the case of the Herbig-Haro objects. In addition, it was established that, in some cases, plasma ejections can consist of several blobs propagating nearly parallel to each other that appear as early as at the stage of plasma pinching. Collision of shock waves generated by each of the blobs leads to the appearance of clumps, which facilitates formation of the lace-like structure of plasma ejection.

The use of Z-pinch facilities makes it possible to carry out well-controlled and diagnosable laboratory experiments to study laboratory jets with scaling parameters close to those of the jets from young stars. This makes it possible to observe processes that are inaccessible to astronomical observations. Such experiments are carried out at the PF-3 facility (“plasma focus,” Kurchatov Institute), in which the emitted plasma emission propagates along the drift chamber through the environment at a distance of one meter. The paper presents the results of experiments with helium, in which a successive release of two ejections was observed. An analysis of these results suggests that after the passage of the first supersonic ejection, a region with a low concentration is formed behind it, the so-called vacuum trace, due to which the subsequent ejection practically does not experience environmental resistance and propagates being collimated. The numerical modeling of the propagation of two ejections presented in the paper confirms this point of view. Using scaling laws and appropriate numerical simulations of astrophysical ejections, it is shown that this effect can also be significant for the jets of young stars.

The paper presents the results of experiments for studying the dynamics and internal structure of an axial plasma jet at the PF-3 facility. Measurements of the azimuthal distribution of the toroidal magnetic field $${{B}_{\varphi }}(\varphi )$$ were carried out. A joint analysis of the experimental base of the obtained distributions $${{B}_{\varphi }}(\varphi )$$ and the optical detection data of the plasma glow from the plasma flow revealed two types of motion observed simultaneously: the azimuthal rotation of individual parts of the plasma flow, as well as the displacement of the central current’s region relative to the axis of the facility’s transit chamber. The angular velocity of plasma rotation is estimated from the data of magnetic measurements and high-speed optical photographic recording. Some features of the current in the head and tail of the flow are revealed. It is shown that the results obtained are consistent with the MHD theory of jets ejected from young stars.

The results of experiments on the study of the features of the dynamics and internal structure of the axial plasma ejection at the PF-3 facility carried out within the program for the laboratory simulation of astrophysical jets are presented. The distribution of the toroidal magnetic field in the radial Bφ(r) and axial Bφ(z) directions was measured. It is shown that the magnetic field plays a significant role in the collimation of the plasma flow, which is important for the verification of numerical models of the propagation of astrophysical jets. The measurements of magnetic fields with spatial resolution along the axis of the fly-by chamber make it possible to determine the length of the region with the captured magnetic flux. Studies of the radial structure of the central part of the plasma ejection indicate an increase in the diameter of the central current flow channel in the direction from the head to the tail of the plasma flow. The approximately linear magnetic field distribution in the form of a dependence Bφ(r) ~ r in the region of the central current flow indicates a uniform distribution of the current density along the radius. Some features of the current flow in the head and tail of the flow are revealed. The interaction of the plasma flow with the structural elements of the fly-by chamber is discussed.

This paper is a sequel to the 1998 review paper “Scientific status of the Dense Plasma Focus” with 16 authors belonging to 16 nations, whose initiative led to the establishment of the International Center for Dense Magnetized Plasmas (ICDMP) in the year 2000. Its focus is on understanding the principal defining characteristic features of the plasma focus in the light of the developments that have taken place in the last 20 years, in terms of new facilities, diagnostics, models, and insights. Although it is too soon to proclaim with certainty what the plasma focus phenomenon is, the results available to date conclusively indicate what it is demonstrably not. The review looks at the experimental data, cross-correlated across multiple diagnostics and multiple devices, to delineate the contours of an emerging narrative that is fascinatingly different from the standard narrative, which has guided the consensus in the plasma focus community for several decades, without invalidating it. It raises a question mark over the Fundamental Premise of Controlled Fusion Research, namely, that any fusion reaction having the character of a beam-target process must necessarily be more inefficient than a thermonuclear process with a confined thermal plasma at a suitably high temperature. Open questions that need attention of researchers are highlighted. A future course of action is suggested that individual plasma focus laboratories could adopt in order to positively influence the future growth of research in this field, to the general benefit of not only the controlled fusion research community but also the world at large.

This paper provides the results of studies of plasma flows generated in the plasma focus facility PF-1000U. Regimes are found, involving the formation of compact plasma objects propagating in the variable-density background environment to the distances exceeding the initial crosswise dimensions of these objects by dozens of times. It is shown that the flow spreads with its proper captured toroidal magnetic field. The plasma flow front structure is studied. The conclusions about the role of radiation cooling and magnetic confinement in the collimation and stability of outflows are drawn. The results obtained in this work can be used to analyze the existing and build new models describing the collimation and stability of non-relativistic outflows of young stellar objects. Copyright (C) EPLA, 2020

This paper presents the most important results of recent plasma studies performed within the PF-1000U facility at the IPPLM in Warsaw, Poland. It was shown that a conical-tip of the anode facilitates the pinch formation and induces an increase in the total neutron yield, while the use of an anti-anode shortens the pinch column but does not improve the fusion-neutron emission. Experiments confirmed that the initial gas conditions have a strong influence on plasma parameters and, at some conditions, the local electron temperatures can reach high values ranging between 5 and 8 keV. It was shown that PF-1000U discharges with the H-2-filling generate intense proton beams which can be used for research on (p-B-11) fusion reactions. It was also demonstrated that at the appropriate gas puffing the PF-1000U facility generates long plasma jets which can be used for simulations of astrophysical phenomena. Research on interactions of intense plasma streams with different solid targets showed that the facility can be useful for material engineering, e.g. for studies of plasma facing components of a future thermonuclear reactor DEMO. Measurements of fast deuteron beams provided information about their angular distribution and energy spectra. The evolution of a pinch column during the emission of charged particle beams was also observed and analyzed.

This paper presents the results of studies of plasma flow parameters on the PF-1000U facility. A distinctive feature of this facility is the ability to create profiled initial gas distributions using gas puffs. In the experiments described, a combined system for filling the vacuum chamber with a working gas was used, in which an additional injection of various gases (deuterium, helium, neon and their mixtures) into the axial region of the chamber prefilled with deuterium was performed using a pulse valve. Thus, both the pinching processes and, accordingly, the generation of axial plasma flows and the conditions of their propagation in the background gas of the facility chamber were affected. Regimes with the generation of compact stable plasma formations propagating over long distances were found. The results obtained can be used in laboratory modelling of astrophysical jets from young stellar objects.

The results of studying the propagation of plasma flows in the surrounding medium performed on the PF-3 plasma focus facility in the laboratory simulation of astrophysical jets from young stellar objects are presented. The modes with the plasma formations which retain their compactness when propagated over significant distances are obtained. The decrement of the flow’s deceleration as a result of its interaction with the background gas is determined. A technique is developed for estimating the plasma temperature by the ratio of radiation intensities from various parts of the spectrum. It is shown that the background gas is heated by the flow radiation, which leads to a change in its ionization state. Thus, the plasma flow propagates not in a neutral gas but in a weakly ionized plasma.