Search

PLOS ONE 17(1), e0262110 (2022). doi:10.1371/journal.pone.0262110, Published by PLOS, San Francisco, California, US

Plasma in a pinch column, as produced by a plasma-focus discharge at the deuterium filling and the current intensity reaching 1 MA, was investigated at the total neutron yield reaching about 10 10 per discharge. The use was made of neutron diagnostics, laser interferometry, soft X-ray measurements, optical emission spectroscopy, magnetic probes, as well as electron and ion measurements with the temporal, spatial, and energetic resolutions. The detailed studies showed the ordered toroidal, helical, and plasmoidal structures which could contain currents with poloidal and toroidal components and their associated magnetic fields. Their spontaneous transformations were explained by changes in a topology of magnetic field lines due to magnetic reconnections. A nonthermal acceleration of fast electrons and ions (producing hard X-rays and fusion neutrons, respectively) corresponded to: 1) the formation of plasmoids in the pinch column and 2) a decay of pinch constrictions and secondary plasmoids during the evolution of instabilities. A filamentary structure of the current flow could explain the high energy density and fast transformations of the magnetic energy into kinetic energy of electron and ion beams (reaching energy of hundreds of kiloelectronvolt). This paper summarizes the results obtained with the PF-1000 facility in 2009-2017, and describes the internal transformations in a dense plasma column during the evolution of MHD instabilities.

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.

Objective The present study aimed to assess the long-term safety and tolerability of valsartan in hypertensive children aged 6–17 years, with or without chronic kidney disease (CKD). Methods This was an 18-month, open-label, multicentre, prospective study conducted in 150 patients with history of hypertension with or without CKD. The primary endpoint was long-term safety and tolerability of valsartan and valsartan-based treatments, assessed in terms of adverse events (AEs), serious AEs, laboratory measurements, estimated glomerular filtration rate (eGFR), urinalysis and electrocardiogram. Results Of 150 enrolled patients, 117 (78%) completed the study. At week 78, a clinically and statistically significant reduction in mean sitting systolic and diastolic blood pressures was observed in all patients (− 14.9 mmHg and − 10.6 mmHg, respectively). Within the first 3 months of treatment, mean urine albumin creatinine ratio decreased in CKD population, which was sustained. A higher percentage of CKD patients had at least one AE compared to non-CKD patients (85.3% vs. 73.3%, respectively). The majority of AEs were mild (50.7%) or moderate (18.7%) in severity. As expected, in patients with underlying CKD, increases in serum potassium, creatinine and blood urea nitrogen were more commonly reported compared to non-CKD patients. A > 25% decrease in Schwartz eGFR was observed in 28.4% of CKD patients and 13.5% of non-CKD patients. Conclusions Valsartan was generally well tolerated, with an AE profile consistent with angiotensin receptor blockers in the overall population and in patients with underlying CKD. Long-term efficacy was maintained and a beneficial effect on proteinuria was observed.

The paper summarizes important results of the recent experimental studies performed on the plasma-focus PF-1000 facility operated in Warsaw, Poland, mainly with the pure deuterium filling. Attention is focused on the evolution of toroidal and plasmoidal self-organized structures formed by internal closed currents inside the dense plasma column. The production of hard x-rays and neutrons corresponds with the formation and decay of plasmoids, in which charged particles can be accelerated effectively to high energies, during a release of the magnetic energy from current filaments of high energy density. It is noticed that the studies of laboratory fusion and cosmic plasmas deal with similar problems, e.g., the fast release of the magnetic energy in a form of high-energy charged particle beams.

In this work, plasma–target interactions on tungsten samples, carried out in a Mather-type plasma focus PF-1000 device, were investigated. The experimental results have been compared to 1D model computer simulations. Samples were studied by means of scanning electron microscopy, focused ion beam microscopy and precise measurements of weight loss. Additionally, simulations based on the numerical solution of a 1D heat conductivity equation were carried out. The samples exhibited relatively high resistance to the generated plasma streams. The practical work indicated a loss of about 1.54 mg per plasma focus discharge. The computer model calculations gave a weight loss one magnitude greater. An attempt to explain this discrepancy is given in the paper.

This paper aims at a test of a plasma focus (PF) device as a metallic plasma jet generator. The experiment was carried out at the DPF-1000U device in which the inner electrode face was conically shaped. Deuterium (D2) with the initial pressure of 0.9 Torr was used as a filling gas. In the experiment, a metallic plasma was ensured due to erosion of the inner electrode during a PF discharge. To create the metallic plasma jet, the eroded copper (Cu) plasma, swept by the deuterium plasma sheath, was accelerated axially and compressed to very small radius (about 1–2 mm). The Cu plasma jet achieved a velocity of 3 × 107 cm/s. To study processes of the plasma jet creation and propagation a 16-frame laser interferometer and a four-frame X-ray pinhole camera were used. Recorded images prove a successful adaptation of the PF device to the metallic plasma jet generator.

This paper describes the structure of a higher extreme ultraviolet (XUV) emission and plasma density region which surrounds a pinched dense-plasma column. It is interpreted as a toroidal-like plasma formation, which is flowing by a closed current with poloidal and toroidal components upon its surface. This current produces a local magnetic field, which separates the external discharge current from the surface of the dense pinch column. We estimated the values of closed currents as well as magnetic- and plasma-pressures in this column and its surrounding on the basis of the measured distribution of interferometric fringes and intense XUV emission, recorded during the pinch stagnation phase. The considered layer forms the region in which the magnetic energy can be conserved, and during its decay, the acceleration of fast deuterons can take place.

The paper discusses a possible energy transformation that leads to the acceleration of fast ions and electrons. In plasma-focus discharges that occur during deuterium filling, which have a maximum current of about 1 MA, the accelerated deuterons produce fast fusion neutrons and fast electrons hard X-ray emissions. Their total energy, which is of the order of several kilojoules, can be delivered by the discharge through a magnetic dynamo and self-organization to the ordered plasma structures that are formed in a pinch during the several hundreds of nanoseconds of the pinch implosion, stagnation, and evolution of instabilities. This energy is finally released during the decay of the ordered plasma structures in the volume between the anode face and the umbrella front of the plasma and current sheath in the form of induced electric fields that accelerate fast electrons and ions.

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.

Human microbiome contains the genetic pool of bacteria and other microbes such as Achaea, fungi and viruses inhabiting the human body. It holds an immense potential to affect both physiological and pathological processes. The microbiome's composition can be defined in detail by analyzing ribosomal 16S rRNA and metagenomic tests. Recent increases in cesar- ean sections, the use of antibiotics during pregnancy, the increasing amount of prematurely born children and changes in infant nutrition have an impact on the microbiome forming process. A correlation between the bowel microbiome's com- position and the occurrence of certain diseases, especially inflammatory bowel diseases (IBD), asthma and type 1 diabetes has been demonstrated. The influence on the development of cognitive functions and behaviour has also been displayed. This correlation justifies attempts to restore the beneficial the composition of the microbiome through the use of probiotics, vaginal microflora transfer in case of cesarean section and encouraging breastfeeding. Development of multiple studies on the topic of the human microbiome and its impact on the human body is necessary in order to reach final conclusions. The aim of this article is to summarize recent findings regarding the development of the human microbiome from the first days of life and the influence of changes in its composition on human health.

Fusion plasmas produced in tokamaks, inertial-fusion experiments with powerful lasers, and z-pinch discharges, deal with similar questions concerning the generation of high energy beams of charge particles, similar to those emitted from plasmas in Universe1-3. In all cases, a fast release of magnetic energy during magnetic reconnections of various organized structures is often considered. Dense plasmas, which are produced in plasma-focus discharges, have some advantages in solving this problem, since they have very convenient parameters for complementary diagnostics with relative simple temporal-, spatial- and spectral-resolution. The described experimental research on DD fusion reactions was performed at the current intensity of about 1 MA and the total neutron yield of about 1010 per shot. A multi-frame interferometry system, scintillation detectors, as well as X -ray and corpuscular diagnostic equipment - made it possible to study the evolution of toroidal- and plasmoidal-structures, which were formed by closed currents with poloidal and toroidal components in filamentary forms. The production of hard X -rays and fusion neutrons correlated with the formation and decay of plasmoids4. The gained knowledge about evolution of the ordered structures, transformations of currents and magnetic fields - can be an inspiration for researchers of the tokamak- and laser-fusion as well as for astrophysicists community.

This paper presents the results of the experimental study of the influence of the applied poloidal magnetic field on the transformation of the plasma column formed by the compression of (10 ± 3)- $\mu \text{g}$ /cm deuterium injected by the gas-puff nozzle in front of the anode axis by the neon plasma sheath of (50 ± 10) $\mu \text{g}$ /cm at a current of 2 MA. The permanent magnet with an initial induction of 20–40 mT placed inside the anode: 1) increased the diameter of the pinch and of the stagnation; 2) depressed the evolution of instabilities and formation of the dense structures in the column; 3) delayed the dip of the current derivative in time (and start of the hard X-ray and neutron emission) 200–300 ns after the first peak of the soft X-ray emission (and the pinch with a minimal diameter near the anode); and 4) decreased the total neutron yield to 10–20%. These results were interpreted in terms of the increase in the repulsive pressure of the compressed poloidal magnetic field, which increases the stabilizing helicity of the discharge current. The transformations are independent of the polarity of the magnet.

Experiments were carried out on the PF-1000 plasma focus device, with a deuterium filling and with deuterium puffing from a gas-puff nozzle placed on the axis of the anode face. The current was reaching 2 MA. 15 interferometric frames from one shot were recorded with a Nd:YLF laser and a Mach–Zehnder interferometer, with 10–20 ns delay between the frames. As a result, the temporal and spatial distribution of the linear densities and the radial and axial velocities of the moving of plasma in the dense plasma column could be estimated.

In this note experimental studies of tungsten (W) samples irradiated by intense plasma-ion streams are reported. Measurements were performed using the modified plasma focus device DPF-1000U equipped with an axial gas-puffing system. The main diagnostic tool was a Mechelle®900 optical spectrometer. The electron density of a freely propagating plasma stream (i.e., the plasma stream observed without any target inside the vacuum chamber) was estimated on the basis of the half-width of the Dβ spectral line, taking into account the linear Stark effect. For a freely propagating plasma stream the maximum electron density amounted to about 1.3 × 1017 cm−3 and was reached during the maximum plasma compression. The plasma electron density depends on the initial conditions of the experiments. It was thus important to determine first the plasma flow characteristics before attempting any target irradiation. These data were needed for comparison with plasma characteristics after an irradiation of the investigated target. In fact, spectroscopic measurements performed during interactions of plasma streams with the investigated W samples showed many WI and WII spectral lines. The surface erosion was determined from mass losses of the irradiated samples. Changes on the surfaces of the irradiated samples were also investigated with an optical microscope and some sputtering and melting zones were observed.

Soft X-ray imaging is a very useful diagnostic technique in plasma-focus (PF) experiments. This paper reports results of four experimental sessions which were carried out at the DPF-1000U plasma-focus facility in 2013 and 2014. Over 200 discharges were performed at various experimental conditions. Measurements were taken using two X-ray pinhole cameras with a line of sight perpendicular to the z-axis, at different azimuthal angles (about 20° and 200°), and looking towards the centre of the PF-pinch column. They were equipped with diaphragms 1000 μm or 200–300 μm in diameter and coated with filters of 500 μm Al foil and 10 μm Be foil, respectively. Data on the neutron emission were collected with silver activation counters. For time-resolved measurements the use was made of four PIN diodes equipped with various filters and oriented towards the centre of the PF-column, in the direction perpendicular to the electrode axis. The recorded X-ray images revealed that when the additional gas-puff system is activated during the discharge, the stability of the discharge is improved. The data collected in these experiments confirmed the appearance of a filamentary fine structure in the PF discharges. In the past years the formation of such filaments was observed in many Z-pinch type experiments. Some of the recorded X-ray images have also revealed the appearance of the so-called hot-spots, i.e. small plasma regions of a very intense X-ray emission. Such a phenomenon was observed before in many PF experiments, e.g. in the MAJA-PF device, but it has not been investigated so far in a large facility such as the DPF-1000U. The time-resolved measurements provided the evidence of a time lapse between the X-ray emission from plasma regions located at different distance from the anode surface. The formation of distinct ‘hot-spots’ in different instants of the DPF-1000U discharge was also observed.

The results are presented of the optical spectra measurements for free plasma streams generated with the use of the modified DPF-1000U machine. This facility was recently equipped with a gas injection system (the so-called gas-puff) placed on the symmetry axis behind the central opening in the inner electrode. The DPF-1000U experimental chamber was filled up with pure deuterium at the initial pressure of 1.6 or 2.4 mbar. Additionally, when the use was made of the gas-puff system about 1 cm3 of pure deuterium was injected at the pressure of 2 bars. The gas injection was initiated 1.5 or 2 ms before the triggering of the main discharge. The investigated plasma discharges were powered from a condenser bank charged initially to 23 kV (corresponding to the energy of 352 kJ), and the maximum discharge current amounted to about 1.8 MA. In order to investigate properties of a dense plasma column formed during DPF-1000U discharges the use was made of the optical emission spectroscopy. The optical spectra were recorded along the line of sight perpendicular to the vacuum chamber, using a Mechelle®900 spectrometer. The recent analysis of all the recorded spectra made it possible to compare the temporal changes in the electron density of a freely propagating plasma stream for discharges without and with the gas-puffing. Using this data an appropriate mode of operation of the DPF-1000U facility could be determined.

In this note we describe measurements of ion beams emitted along the z-axis of the DPF-1000U facility operated at 23 kV, 334 kJ, and with the initial deuterium pressure of 1.6–2 hPa. The DPF-1000U device was recently renewed and equipped with a dynamic gas-puff valve placed inside the inner electrode. The investigated ions were recorded by means of ion pinhole cameras equipped with solid state nuclear track detectors of the PM-355® (PADC) type. The energy spectra of ions were determined using a Thomson spectrometer placed on the symmetry axis at a distance of 160 cm from the electrodes outlets. The ion images recorded during discharges performed under different experimental conditions show that the ion beams have a complex structure, usually in the form of a central bunch and an annular stream composed of many micro-beams. Energies of the registered deuterons have been in the range of 30–700 keV, while the fast protons (which originated from the hydrogen remnants) had energies in the range of 300–850 keV.

Results of measurements of magnetic fields in the plasma pinching region during the compression of the deuterium plasma current sheath (PCS) at the PF-1000 plasma focus facility are presented. The fine structure of the PCS (shock wave-magnetic piston) and its variations in the course of plasma compression toward the facility axis are studied using magnetic probes and laser interferometry. The radial distributions of the plasma density and current in the PCS are compared. It is shown that, in the shock wave region, the electron density of the compressed plasma is on the order of ∼1018 cm−3, whereas the PCS current is almost entirely concentrated in the magnetic piston region—a plasma layer with an electron density of less than 1015 cm−3. Efficient transportation of the current by the PCS into the axial region of the facility in discharges with a high neutron yield (Yn > 1011 neutrons/shot) is detected. It is shown that the total neutron yield is well described by the dependence Yn ≈ (1.5–3) × 1010Ip4, where Ip is the pinch current (in MA) flowing within the region r ≤ 13 mm.

Principal Component Analysis has been employed in order to find correlations between different quantities (related to spectroscopy in visible range, neutron yield and the time derivative of the current) describing Z-pinch plasma in the PF-1000 installation. Set of measurements in various plasma conditions has been taken into account. Strong correlation between level of impurity content and neutron yield has been found.

This paper concerns the evolution of internal structures and the neutron production in plasma-focus discharges performed in the presence of a permanent magnet (placed inside the anode front) and within a residual magnetic field (after the removal of this magnet). The initial magnetic field generated by this magnet prevented: (i) the effective compression of a dense pinch column, (ii) the formation of plasma organized structures, and (iii) the evolution of plasma instabilities. The experimental results have shown an increase in the initial magnetic field due to a magnetic dynamo effect in the presence of the permanent magnet, as well as in a series of shots performed after its removal. It was observed that the appearance of plasmoidal structures is necessary for the emission of fusion neutrons. A characteristic quasicylindrical plasma layer of the radius corresponding to the plasma lobule tops, which might be identified with a ring region of the acceleration of fast deuterons, was also observed.

This paper presents the discussion concerning the characteristics of the fast deuterons which have energy above 30 keV and are recorded during high-current plasma-focus (PF) discharges, by means of PM-355 plastic track-detectors placed inside ion pinhole cameras. The fast deuterons evoke D-D fusion reactions, mainly by a beam-target mechanism. The distribution of the magnetic field, which influences the trajectories of the recorded deuterons, is discussed. It is found that the fast deuterons are produced in various local sources and their motion is strongly influenced by a circular symmetry of the local magnetic field, which increases their radial shift with a decrease in their energy. The sources of these deuterons are probably located inside the plasmoids and in some local regions of the ring-shaped plasma structures. These ring-structures can be formed outside the dense pinch column, up to a radius of 5 cm. Global magnetic fields, associated with the total current flow in the PF discharge, have a weaker influence. The observed radial shift of the recorded fast deuterons is interpreted as a result of their deflection by magnetic fields which have opposite orientations of the azimuthal components, associated with the currents flowing in directions towards and from the applied ion detectors. The local sources of the recorded fast deuterons correspond to filamentary structures, in which the stored magnetic energy (having the local high density) can be released in induced electric fields accelerating the deuterons during the magnetic reconnections.This paper presents the discussion concerning the characteristics of the fast deuterons which have energy above 30 keV and are recorded during high-current plasma-focus (PF) discharges, by means of PM-355 plastic track-detectors placed inside ion pinhole cameras. The fast deuterons evoke D-D fusion reactions, mainly by a beam-target mechanism. The distribution of the magnetic field, which influences the trajectories of the recorded deuterons, is discussed. It is found that the fast deuterons are produced in various local sources and their motion is strongly influenced by a circular symmetry of the local magnetic field, which increases their radial shift with a decrease in their energy. The sources of these deuterons are probably located inside the plasmoids and in some local regions of the ring-shaped plasma structures. These ring-structures can be formed outside the dense pinch column, up to a radius of 5 cm. Global magnetic fields, associated with the total current flow in the PF discharge, have a weake...

Circulating endothelial progenitor cells (EPC) are bone marrow derived progenitors that can be mobilized by erythropoietin or in response to tissue injury, and participate in vascular repair. EPC are understudied in human neonates. Whether EPC frequency in newborn infants may be influenced by gestational age or postnatal stress is unknown.Blood samples were collected on day 1 of life and weekly for 3 weeks from hospitalized neonates for plasma erythropoietin and flow cytometry analysis for CD34+, CD34+CD45-, CD34+VEGFR2+ and CD34+CD45-VEGFR2+ cells (EPC). Associations between CD34+ cell subsets and clinical parameters were studied.Forty five patients were enrolled. An inverse correlation with gestational age was observed for CD34+ and CD34+ VEGFR2+ cell frequencies in whole blood (WB) on day 1 (p0.05). In preterm infants, CD34+ cell frequency decreased with increased postnatal age (p=0.0001) and CD34+VEGFR2+ cell frequency was higher at week 3 than on day 1 in WB (p=0.0002). On day one, CD34+ and CD34+CD45- cell frequencies in the mononuclear cell fraction (MNC) were higher in preterm than term infants (p=0.035 and p=0.049, respectively) but CD34+CD45-VEGFR2+ cell frequency (median 2.2/million MNC versus 3.8/million MNC) and erythropoietin levels were not significantly different. Transient increases in EPC were observed in five infants with infection. Four preterm infants who developed bronchopulmonary dysplasia had undetectable or low EPC through the first 3 weeks of life.Gestational age and postnatal age influenced circulating CD34+ and CD34+VEGFR2+ but not CD34+CD45-VEGFR2+ (EPC) cell frequencies. Circulating EPC in neonates may be influenced by clinical stress.

The experimental research of fusion DD reaction was provided on the dense plasma focus (DPF) device at the current above 1 MA and the total neutron yield at the level of 1010. The multiframe interferometry and X-ray diagnostics imaged the evolution of toroidal and plasmoidal structures, formed by closed currents with poloidal and toroidal components. The spontaneous evolution starts by the dominant toroidal current, continues by increase of the poloidal component and finished by the dominant poloidal one. The transformations are realized by reconnection of magnetic lines, similarly as in tokamak and astrophysical1 or in laser produced fusion plasmas 2. The ordered structures in DPF are similar to the field reverse and spheromak-like configurations with confined plasma in which the pressure of the pinching current is equaled by the pressures of the compressed plasma and repulsive component of magnetic field. The neutron production of fusion neutrons correlates with the formation and decay of plasmoids. We present the estimation of the radial distribution of the poloidal and toroidal current, its filamentary form3 and the possible acceleration mechanism of fast particles at the release of the part of magnetic energy during reconnection.

The time-varying inductance Lp(t) of the system formed by the coaxial electrodes and the current sheet (CS) in plasma focus (PF) discharges was calculated for the first time by Mather and Bottoms [1] on a 13-kJ PF device in Los Alamos using measured values of V(t) , the voltage at the breach end of the electrodes, and dI/dt, the time derivative of the current circulating through the system. Recently, the same method was applied to assess Lp(t) in devices of lower energy [2]–[4]. This physical magnitude was also used for estimating other relevant parameters, like the voltage drop over the pinch column [5], [6]. The purpose of this paper is to extend this procedure to the high-energy device PF1000, operated by the International Center for Dense Magnetized Plasmas (ICDMP) from Warsaw, Poland, using measurements performed during an experimental campaign conducted in 2013. High-energy devices as PF1000, besides having much larger capacitor banks, also has larger electrodes, which leads to larger gun inductances and consequently higher voltage drops in the pinch. Hence, the goal of the present study is to validate the application of the mentioned technique in large PF devices and also to produce additional information, namely, the behavior of the voltage drop over the pinch plasma column. Fil: Bruzzone, Horacio Abel. Universidad Nacional de Mar del Plata; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Acuña, Hugo Néstor. Universidad Nacional de Mar del Plata; Argentina Fil: Barbaglia, Mario Oscar. Universidad Nacional del Centro de la Provincia de Buenos Aires; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Milanese, Maria Magdalena. Universidad Nacional del Centro de la Provincia de Buenos Aires; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Miklaszewski, Ryszard. Institute of Plasma Physics and Laser Microfusion; Polonia Fil: Paduch, Marian. Institute of Plasma Physics and Laser Microfusion; Polonia Fil: Zielinska, Ewa. Institute of Plasma Physics and Laser Microfusion; Polonia Fil: Clausse, Alejandro. Comision Nacional de Energía Atómica; Argentina. Universidad Nacional del Centro de la Provincia de Buenos Aires; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

Energy transformations are estimated from experimental results obtained on the PF-1000 plasma focus facility operated with a deuterium gas filling and maximum current of 2 MA, which enabled the neutron yield of >; 1011 to be obtained. Use was made of the laser interferometry images and the recorded signals of hard X-rays (HXRs) and neutrons, as well as voltage, current, and current-derivative waveforms. The calculations of the inductance, derivative of inductance, and resistance of the current sheath enabled the evaluation of energy delivered to the plasma. It was estimated that, during the intensive pulses of the HXRs and neutrons, energy of 3-11 kJ is delivered to the plasma column probably through an anomalous resistance at the time closely before and during pulses of HXR and neutron production. A predominant portion of this energy is effectively used for the acceleration of fast deuterons capable of producing fusion neutrons.

Multiframe laser interferometer system for studies of rapidly varying processes in dense, high-temperature plasma in plasma-focus device is described. The setup of sixteen-frame interferometer contains the Mach-Zehnder system and the completely new, innovative beams separator which allows obtaining sixteen interferometric frames in one discharge. Each interferogram is recorded separately with the same linear size and quality. Delay from the first to the last frame is 220 ns. The result obtained using this system is given. It demonstrates its quality and suitability for investigations of dynamics of fast, irreproducible processes in PF-1000 (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The laser interferometry and X-ray diagnostic studies were performed within the PF-1000 facility operated with the maximum current of 2 MA and the deuterium gas filling (ensuring neutron yield above ). At this current, the plasmoidal, helical and toroidal structures were formed inside the plasma column. Some of them penetrated the column surface and later on were dissolved inside the dense plasma column. The period of their life was from a few tens to hundreds of nanoseconds and a plasma density was higher than in neighbor regions. It could be explained as a result of the plasma pinching by a magnetic field originating from the internal currents. Hard X-rays and fusion neutrons were produced during four different phases of plasma column transformations, i.e., in the period of the formation of a dense plasmoid, in the period of an escape of the plasma from the region between the dense structure and anode, during the interruption of the constriction, and during the integration of a “plasma lobule” with the pinch column. Fast electrons and deuterons were probably accelerated at the same region, during the same period of explosions of the plasma structures with a density ranging above . The plasma evolution could be explained by a spontaneous transformation of azimutal and poloidal components of magnetic fields. The poloidal component could be self-generated during the implosion of the current sheath.

Several series of high-current discharges were carried out within the PF-1000U facility at various gas conditions. The initial filling pressures were p0 = 1.2 hPa D2, 1.06 hPa D2 + 10% He, or 0.53 hPa D2 + 25% Ne. The discharges were performed with or without an additional gas puffing. In shots with the puffing, 1 cm3 of gas (or mixture), compressed to the pressure of (0.13–0.20) MPa, was injected 1.5 ms before the discharge initiation. Pure D2, He, Ne, or a mixture of 50% He + 50% Ne was used for puffing. The optical spectroscopic measurements were performed at a distance of 16 or 27 cm from the electrode outlets. Almost all discharges produced a dense plasma-focus (of about 10 cm in length) and a long plasma jet, which was observed for several μs. The ambient plasma density at the investigated gas-conditions was about 1016 cm−3, but an admixture of 10% He or 25% Ne (added to the D2-filling) induced an increase in this density by factor 1.8–2.5. In all the cases, the plasma jet density was above 10-times higher than that of ambient plasma. At the He- or Ne-puffing, this density reached (3.5–6) × 1017 cm−3. Electron temperatures in the plasma jet changed from about 5.0 to about 3 eV in 5–7 μs.

The paper describes the behaviour of plasma within a MA plasma-focus with a novel electrode configuration, in which the anode and anti-anode were both equipped with conical tips. This configuration was applied to test the possibility of reducing the pinch axial dimensions during the radial compression of a current sheath. It made it possible to strengthen a dense plasma jet near the anode end, which ejected plasma into a bigger plasmoidal structure formed in the central pinch region. It did not allow forming an opposite anti-anode jet and stopped the axial motion of this structure. In plasma focus discharges with the deuterium filling, the decay of the anode jet and the corresponding plasmoid evolution were accompanied by the fusion-neutron production. Some results obtained with this configuration have also supported the hypothesis of the acceleration of fast electrons and ions at a release of the magnetic energy during magnetic reconnections in the organized dense plasma structures.

This paper considers regions of a fast deuteron production in a correlation with an evolution of ordered structures inside a pinch column of a mega-ampere plasma focus discharge. Ion pinhole cameras equipped with plastic PM-355 track-detectors recorded fast deuterons escaping in the downstream and other directions (up to 60° to the z-axis). Time-integrated ion images made it possible to estimate sources of the deuteron acceleration at the known magnetic field and deuteron energy values. The images of the fast deuterons emitted in the solid angle ranging from 0° to 4° showed two forms: central spots and circular images. The spots of 1–2 cm in diameter were produced by deuterons from the central pinch regions. The circular-shaped images of a radius above 3 cm (or their parts) were formed by deuterons from the region surrounding the dense pinch column. The ion pinhole cameras placed at angles above 20° to the z-axis recorded the ion spots only, and the ring-images were missing. The central region of the deut...

A plasma column generated in the PF-1000 device working in deuterium gas at a current level of 1 MA was investigated with interferometric diagnostics and scintillation detectors. The beam of diagnostic laser of 527-nm wavelength was optically split into 16 beams with a time delay in the range from 0 to 220 ns. This diagnostic tool makes possible the imaging of the evolution of pinch geometry, the axial and radial distributions of plasma density in the column at the stagnation phase, and their comparison with the evolution of X-ray and neutron production. The evolution of dense structure is described with respect to its importance for fusion processes.

IL-7 is critical for B cell production in adult mice; however, its role in human B lymphopoiesis is controversial. One challenge was the inability to differentiate human cord blood (CB) or adult bone marrow (BM) hematopoietic stem cells (HSCs) without murine stroma. Here, we examine the role of IL-7 in human B cell development using a novel, human-only model based on coculturing human HSCs on primary human BM stroma. In this model, IL-7 increases human B cell production by >60-fold from both CB and adult BM HSCs. IL-7-induced increases are dose-dependent and specific to CD19+ cells. STAT5 phosphorylation and expression of the Ki-67 proliferation Ag indicate that IL-7 acts directly on CD19+ cells to increase proliferation at the CD34+ and CD34− pro-B cell stages. Without IL-7, HSCs in CB, but not BM, give rise to a small but consistent population of CD19lo B lineage cells that express EBF (early B cell factor) and PAX-5 and respond to subsequent IL-7 stimulation. Flt3 ligand, but not thymic stromal-derived lymhopoietin (TSLP), was required for the IL-7-independent production of human B lineage cells. As compared with CB, adult BM shows a reduction of in vitro generative capacity that is progressively more profound in developmentally sequential populations, resulting in an ∼50-fold reduction in IL-7-dependent B lineage generative capacity. These data provide evidence that IL-7 is essential for human B cell production from adult BM and that IL-7-induced expansion of the pro-B compartment is increasingly critical for human B cell production during the progression of ontogeny.

The identity and lineage potential of the cells that initiate thymopoiesis remain controversial. The goal of these studies was to determine, at a clonal level, the immunophenotype and differentiation pathways of the earliest progenitors in human thymus. Although the majority of human CD34+lin− thymocytes express high levels of CD7, closer analysis reveals that a continuum of CD7 expression exists, and 1% to 2% of progenitors are CD7−. CD34+lin− thymocytes were fractionated by CD7 expression and tested for lineage potential in B-lymphoid, T-lymphoid, and myeloid-erythroid conditions. Progressive restriction in lineage potential correlated with CD7 expression, that is, the CD7hi fraction produced T and NK cells but lacked B and myelo-erythroid potential, the CD7int (CD10+) fraction produced B, T, and NK cells, but lacked myelo-erythroid potential. The CD7− fraction produced all lymphoid and myelo-erythroid lineages and expressed HSC-associated genes. However, CD34+lin−CD7− thymocytes also expressed early T lymphoid genes Tdt, pTα, and IL-7Rα and lacked engraftment capacity, suggesting the signals that direct lymphoid commitment and corresponding loss of HSC function are rapidly initiated on arrival of HSC in the human thymus. Thus, differential levels of CD7 identify the progressive stages of lineage commitment in human thymus, initiated from a primitive CD7− lympho-myeloid thymic progenitor.

The experimental research of fusion DD reaction was provided on the plasma focus device PF-1000 in IPPLM in Warsaw, Poland at the current of 2 MA. The multiframe interferometry diagnostics showed existence of the dense internal structures of spherical-, toroidal-, helical- and disclike forms in the column. The magnetic probe measurements enabled to combine these structures with internal poloidal and toroidal magnetic fields. The neutron diagnostics with temporal resolution made possible to correlate the neutron production with the evolution of the plasmoids and constrictions. These transformations can be interpreted by the scenario of closed internal poloidal and toroidal currents1. In this contribution we present evolution of some lobules, top of which returns back to the dense column. We elucidated this arcade on the base of the existence of the poloidal and toroidal closed currents outside the dense pinched column. These loops transport the discharge current to the higher distance from the column and their magnetic field is a reservoir of the magnetic energy which can be released at the acceleration of the fast particles.

The paper reports on recent measurements of the X-ray emission from a large plasma-focus PF-1000U facility [1] and compares them with results from the old Poseidon device [2]. The most important results of time-integrated measurements, which were performed by means of an X-ray pinhole camera, are presented and analyzed. Attention is paid to studies of a fine structure of the collapsing current sheath and dense pinch column. Observations of plasma filaments and so-called “hot spots” are discussed. The first observation of plasma filaments inside the PF pinch column [3] was later confirmed by some small-scale PF experiments, but in the large PF-1000U facility plasma filaments have for the first time been recorded recently. Other new results are time-integrated X-ray images of PF-1000U discharges with the gas puffing, which in some cases show very distinct “hot spots” formed outside the dense pinch core. They are explained by local neckings of spiral current filaments which surround the central pinch column.

The present paper presents a high-speed photography sub-system which allows recording of frame sequence and streak images of plasma in a narrow band of the visible spectrum with high temporal and spatial resolution. Two methods are proposed for determining the distribution of the electron temperature or electron density of the plasma sheath originating in the plasma-focus phenomenon. These methods are based on theoretical considerations and processing of the results of experiments using a high-speed photography sub-system. A comparison between an experimental study of the plasma sheath structure and calculations obtained using magnetohydrodynamic (MHD) code is presented. Detailed explanations and considerations are exemplified by a number of results obtained both in experimental investigations and in numerical calculations.

The paper presents the results of recent experiments performed within the PF-1000 facility. The main goal of these investigations was to determine the neutron emission characteristics, which could enable an approximate settlement of the problem of the neutron emission mechanism. Three scintillation probes, located at different angles (7 m from the electrode outlet), were used to perform time-resolved measurements of the hard X-ray radiation and neutron emission. Time-resolved X-ray signals were measured by means of PIN diodes covered with different filters, and they were compared with other traces (voltage waveforms, dI/dt signals, and neutron-induced pulses) in order to determine their correlations.

The paper describes the evolution of self-organized structures inside a pinched plasma column during the phase of the effective production of fusion neutrons, as observed in the mega-ampere plasma focus experiment performed with a conical tip placed in the centre of the anode face. In a comparison with the plane anode face configuration, the described anode shape facilitated transformations in the pinch column during the neutron production and increased the neutron yield several times. Simultaneously, it decreased the minimal diameter and the length of the pinched column, and it depressed the first neutron pulse. It also induced shorter pulses of X-rays and neutrons, which enabled the determination of a temporal difference between the emission of electron and deuteron beams. The fast electrons were produced mainly during a disruption of the pinch constriction, while the fast deuterons – during the formation and explosion of plasmoids. The paper also presents the temporal evolution of a current distributio...

The paper concerns important differences in the evolution of plasma column structures during the production of fusion neutrons in the first and subsequent neutron pulses, as observed for plasma-focus discharges performed with the deuterium filling. The first neutron pulse, of a more isotropic distribution, is usually produced during the formation of the first big plasmoid. The next neutron pulses can be generated by the fast deuterons moving dominantly in the downstream direction, at the instants of a disruption of the pinch constriction, when other plasmoids are formed during the constriction evolution. In both cases, the fusion neutrons are produced by a beam-target mechanism, and the acceleration of fast electron- and deuteron-beams can be interpreted by transformation and decay of the magnetic field associated with a filamentary structure of the current flow in the plasmoid.

The experimental research of fusion DD reaction was provided on the plasma focus device at the current of 2 MA in the approach with the MagLIF conception. The deuterium injected from the gas-puff in the axis of the anode and compressed by neon plasma sheath was studied with the multiframe x-ray and interferometry diagnostics. The total neutron yield at the level of 1010 – 1011 per shot was registered at the compression of about 7 µg/cm of the deuterium from the gas-puff by about 23 µg/cm of the neon plasma sheath. The addition of the puffing deuterium to the filling neon in the chamber decreased the soft X-ray emission about two orders. This decrease can be explained by the absence of the neon and the presence of the deuterium in the central structures during their formation and transformation. The separation of both gases should be caused by internal closed currents magnetizing the plasma. The neutrons were produced both at the initial phase of stagnation, as well as at a later time in the evolution of instabilities.

The paper describes the application of SSNTDs of the PM-355 type to diagnostics of reaction products emitted from high-temperature deuterium plasmas produced in Plasma Focus (PF) facilities. Acceleration processes occurring in plasma lead often to the generation of high-energy ion beams. Such beams induce nuclear reactions and contribute to the emission of fast neutrons, fusion protons and alpha particles from PF discharges with a deuterium gas. Ion measurements are of primary importance for understanding the mechanisms of the physical processes which drive the charged-particle acceleration. The main aim of the present studies was to perform measurements of spatial- and energy-distributions of fusion-reaction protons (about 3 MeV) within a PF facility. Results obtained from energy measurements were compared with the proton-energy spectra computed theoretically. The protons were measured by means of a set of ion pinhole cameras equipped with PM-355 detectors, which were placed at different angles relative to the electrode axis of the PF facility.

Optical emission spectroscopy techniques were used to investigate the spectra of dense deuterium-plasma jets generated by high-current pulse discharges within the large PF-1000U facility and to estimate parameters of plasma inside the jets and their surroundings. Time-resolved optical spectra were recorded by means of a Mechelle®900 spectrometer. From an analysis of the deuterium line broadening, it was estimated that the electron concentration at a distance 57 cm from the electrode outlets amounted to (0.4–3.7) × 1017 cm−3 depending on the initial gas distribution and the time interval of the spectrum registration after the instant of the plasma jet generation. From the re-absorption dip in the Dβ profile, it was assessed that the electron concentration in the surrounding gas was equal to about 1.5 × 1015 cm−3. On the basis of the measured ratio of He II 468.6 nm and He I 587.6 nm line intensities, it was estimated that the electron temperature amounted to about 5.3 eV. Also estimated were some dimension...

The paper describes the evolution of the ordered dense toroidal- and plasmoidal-like structures in a pinch column and the hard X-ray emission from mega-ampere dense plasma-focus discharges performed at the helium (He) filling. Some shots were carried out with an Al-wire of 270 μm in diameter, which was placed along the z-axis in the front of the anode face. The evolution of the considered structures was investigated by means of a multi-frame laser interferometer system as well as the X-ray diagnostics, and it was compared with their evolution observed earlier at the deuterium (D2) filling. In He-plasma, the ions had a higher mass and Z-number, and at the same initial filling pressure, the velocity of plasma transformations was decreased, but the stability of the investigated structures, as well as the self-generated azimuthal current component and the soft X-ray radiation were increased. The distribution of the plasma electron density (determined from the interferometric images) made it possible to estima...

The paper presents results of experimental studies of dense and high-temperature plasmas, which were produced by pulsed high-current discharges within a modernised PF-1000U facility operated at different initial gas conditions, and supplied from a condenser bank which delivered energy of about 350 kJ. The investigated discharges were performed at the initial deuterium filling under pressure of 1.6–2.0 hPa, with or without an additional puffing of pure deuterium (1 cm3, under pressure 0.15 MPa, at instants 1.5–2 ms before the main discharge initiation). For a comparison discharges were also performed at the initial neon filling under pressure of 1.1–1.3 hPa, with or without the addition of deuterium puffing. The recorded discharge current waveforms, laser interferometric images, signals of hard x-rays and fusion neutrons, as well as time-integrated x-ray pinhole images and time-resolved x-ray signals were compared. From a ratio of the x-ray signals recorded behind beryllium filters of different thickness there were estimated values of a plasma electron temperature (T e) in a region at the electrode outlets. For pure deuterium discharges an averaged T e value amounted to 150–170 eV, while for neon discharges with the deuterium puffing it reached 330–880 eV (with accuracy of ±20%).