Plasma Structures Research Articles

New evidence about the nature of plasma filaments in plasma accelerators of type plasma-focus

In this work, new evidence and information about both the origin and evolution of filamentary structures observed in the current sheath of a small plasma focus (PF) discharge are reported. The experiments were carried out in a small generator of low energy (multipurpose generator) at the PF configuration, under different operating conditions. These include different anode and insulator geometries, without return bars and in a high-performance regime of the generator at high pressures (10 mbar). The evolution of the plasma structures is characterized by means of refractive optical techniques. The electrical behavior of the discharge, as well as its performance, are monitored with conventional electrical diagnostics and neutron and x-ray detectors, respectively. Plasma filaments of the same species are present in all tested configurations, however, in experiments with larger effective anode length (and smaller anode radii), the plasma region containing the filaments moves away from the anode surface and remains confined in a region of the plasma sheath, such as a toroidal plasma belt, without reaching the top of the anode nor participating in the radial compression phase. According to images of the plasma sheath in its early phase, the filaments originate and evolve from a precursor annular plasma formed in the lower part of the anode next to the insulator, during the process of electrical breakdown. The local character that these dense-filamentary structures acquire in the evolution of the plasma sheath would discard the current-filament hypothesis. On the other hand, experiments performed in deuterium gas with anodes of larger effective lengths and without filaments in the radial compression phase allowed the production of neutrons and x-rays at a high performance.

Direct observations of a complex coronal web driving highly structured slow solar wind

The solar wind consists of continuous streams of charged particles that escape into the heliosphere from the Sun, and is split into fast and slow components, with the fast wind emerging from the interiors of coronal holes. Near the ecliptic plane, the fast wind from low-latitude coronal holes is interspersed with a highly structured slow solar wind, the source regions and drivers of which are poorly understood. Here we report extreme-ultraviolet observations that reveal a spatially complex web of magnetized plasma structures that persistently interact and reconnect in the middle corona. Coronagraphic white-light images show concurrent emergence of slow wind streams over these coronal web structures. With advanced global magnetohydrodynamics coronal models, we demonstrate that the observed coronal web is a direct imprint of the magnetic separatrix web (S-web). By revealing a highly dynamic portion of the S-web, our observations open a window into important middle-coronal processes that appear to play a key role in driving the structured slow solar wind.

Multiscale Features of Magnetic Field Fluctuations and Field-Aligned Currents in the Polar Ionosphere: A Case Study

Complexity is a typical feature of space plasmas that may involve the formation of multiscale coherent magnetic and plasma structures. The winding features (pseudo-polarization) of magnetic field fluctuations at different spatial scales are a useful quantity in this framework for investigating complexity in space plasma. Indeed, a strong link between pseudo-polarization, magnetic/plasma structures, turbulence and dissipation exists. We present some preliminary results on the link between the polarization of the magnetic field fluctuations and the structure of field-aligned currents in the high-latitude ionosphere. This study is based on high-resolution (50 Hz) magnetic field data collected on board the European Space Agency Swarm constellation. The results show the existence of a clear link between the multiscale coarse-grained structure of pseudo-polarization and intensity of the field-aligned currents, supporting the recent findings according to which turbulence may be capable of generating multiscale filamentary current structures in the auroral ionosphere. This feature is also examined theoretically, along with its significance for the rate of energy deposition and heating in the polar regions.

Surface plasmon-enhanced photodetection of monolayers MoS2 on an ion beam modified functional substrate

Monolayer molybdenum disulfide (1L-MoS2) is considered a potential optoelectronic device material due to its ultrathin and direct bandgap properties. However, the absorption of incident light by 1L-MoS2 has shown to be relatively low and is not sufficient to implement high photoelectric conversion efficiency, limiting its practical applications in photodetectors. Due to the local surface plasmon resonance effect, the integration of plasma nanoparticles (NPs) with 2D materials may provide a promising method for enhancing light–matter interactions. Nevertheless, MoS2 may undergo fold deformation when transferred to the plasma structure when prepared via conventional strategies, resulting in the introduction of larger defects. In this work, we reported on a photodetector with enhanced MoS2 photoresponsivity on a flat plasmon functional substrate, in which the Ag NPs were embedded into fused silica (SiO2) by ion implantation. Using MoS2/Ag NPs:SiO2 architecture, the photocurrent of the MoS2-based photodetector was significantly improved under incident light of 375, 532, and 635 nm, with a maximum increase of 72.8 times, while the response time also decreased to a certain extent. Furthermore, the plasma functional substrate had the advantages of environmental stability and repeatable recycling, allowing it to be easily integrated with different 2D materials. Thus, this work offered a viable path for realizing efficient photodetectors based on 2D material.

Rare earth effect on laser produced plasma dynamics during pulsed laser deposition of doped cobalt ferrite

The addition of rare earth elements the ferrites can lead to significant changes in structural, magnetic and electric properties of bulk materials and also of thin films deposited by pulsed laser deposition. The present study relies on the analysis of the laser induced plasma of three sets of cobalt ferrite targets doped with various concentrations of RE elements (Dy, Gd, Yb) and proposes a correlation of the derived results with structural investigations of the films obtained during the same experiment. ICCD imaging and space-and time-resolved optical emission spectroscopy techniques were used to obtain information on the dynamics and excitation temperatures of various species found in the laser produced plasmas (LPP). Initial investigations on the global behavior of the LPP revealed that the addition of RE reduced the drift velocities of the formed plasma structures, the lowest ones being observed for the targets doped with the heaviest RE (Yb). Space-and time-resolved spectroscopy measurements applied for all main elements (Fe, Co and RE - both neutral and ionic species) showed a complex dynamic system, with decreased/increased kinetic energies for neutrals/ions at high dopant concentrations, suggesting a possible re-sputtering effect at the films surface. The individual excitation temperatures of the main elements derived from Boltzmann plots increased as the RE content was augmented via radiative collision events due to their larger diameters compared with Co, Fe or O. The spatial distribution of electron temperature can be explained by the charge separation occurring with the addition of RE in the investigated systems.

Editorial: Structure and dynamics of atmospheric, plasma, and astrochemical molecular processes

Editorial: Structure and dynamics of atmospheric, plasma, and astrochemical molecular processes

The Effect of Thermal Misbalance on Slow Magnetoacoustic Waves in a Partially Ionized Prominence-Like Plasma

Solar prominences are partially ionized plasma structures embedded in the solar corona. Ground- and space-based observations have confirmed the presence of oscillatory motions in prominences, which have been interpreted in terms of standing or propagating MHD waves. Some of these observations suggest that slow magnetoacoustic waves could be responsible for these oscillations and have provided us with evidence about their damping/amplification with very small ratios between damping/amplifying times and periods, which have been difficult to explain from a theoretical point of view. Here we investigate the temporal behavior of non-adiabatic, slow, magnetoacoustic waves when a heating–cooling misbalance is present. The influence of optically thin losses and of a general heating term, in which density and temperature dependence can be modified, as well as the effect of partial ionization have been considered. Furthermore, a tentative example of how, using observational data, the observed ratio between damping/amplifying times and periods could be matched with those theoretically obtained is shown. In summary, different combinations of radiative losses, heating mechanisms, and typical wavenumbers, together with the effect of partial ionization, could provide a theoretical tool able to reproduce observational results on small-amplitude oscillations in prominences.

Kilotesla plasmoid formation by a trapped relativistic laser beam.

A strong quasistationary magnetic field is generated in hollow targets with curved internal surface under the action of a relativistically intense picosecond laser pulse. Experimental data evidence the formation of quasistationary strongly magnetized plasma structures decaying on a hundred picoseconds timescale, with the magnetic field strength of the kilotesla scale. Numerical simulations unravel the importance of transient processes during the magnetic field generation and suggest the existence of fast and slow regimes of plasmoid evolution depending on the interaction parameters. The proposed setup is suited for perspective highly magnetized plasma application and fundamental studies.

Hyperfibrinolysis drives mechanical instabilities in a simulated model of trauma induced coagulopathy

IntroductionTrauma induced coagulopathy (TIC) is common after severe trauma, increasing transfusion requirements and mortality among patients. TIC has several phenotypes, with primary hyperfibrinolysis being among the most lethal. We aimed to investigate the contribution of hypercoagulation, hemodilution, and fibrinolytic activation to the hyperfibrinolytic phenotype of TIC, by examining fibrin formation in a plasma-based model of TIC. We hypothesized that instabilities arising from TIC will be due primarily to increased fibrinolytic activation rather than hemodilution or tissue factor (TF) induced hypercoagulation. MethodsThe influence of TF, hemodilution, fibrinogen consumption, tissue plasminogen activator (tPA), and the antifibrinolytic tranexamic acid (TXA) on plasma clot formation and structure were examined using rheometry, optical properties, and confocal microscopy. These were then compared to plasma samples from trauma patients at risk of developing TIC. ResultsCombining TF-induced clot formation, 15 % hemodilution, fibrinogen consumption, and tPA-induced fibrinolysis, the clot characteristics and hyperfibrinolysis were consistent with primary hyperfibrinolysis. TF primarily increased fibrin polymerization rates and reduced fiber length. Hemodilution decreased clot optical density but had no significant effect on mechanical clot stiffness. TPA addition induced primary clot lysis as observed mechanically and optically. TXA restored mechanical clot formation but did not restore clot structure to control levels. Patients at risk of TIC showed increased clot formation, and lysis like that of our simulated model. ConclusionsThis simulated TIC plasma model demonstrated that fibrinolytic activation is a primary driver of instability during TIC and that clot mechanics can be restored, but clot structure remains altered with TXA treatment.

Equivalence between pressure- and structure-defined ionization in hot dense carbon.

The determination of the ionization of a system in the hot dense regime is a long standing issue. Recent studies have shown inconsistencies between standard predictions using average atom models and evaluations deduced from electronic transport properties computed with quantum molecular dynamics simulations [Bethkenhagen et al., Phys. Rev. Res. 2, 023260 (2020)]2643-156410.1103/PhysRevResearch.2.023260. Here, we propose a definition of the ionization based on its effect on the plasma structure as given by the pair distribution function (PDF), and on the concept of effective one-component plasma (eOCP). We also introduce a definition based on the total pressure and on a modelization of the electronic pressure. We show the equivalence of these definitions on two studies of carbon along the 100eV isotherm and the 10g/cm^{3} isochor. Simulations along the 100eV isotherm are obtained with the newly implemented Ext.First principles molecular dynamics (Fpmd) method in Abinit for densities ranging from 1 to 500g/cm^{3}and along the 10g/cm^{3} isochor with the recently published Spectral quadrature DFT (Sqdft) simulations, between 8 and 860eV. The resulting ionizations are compared to the predictions of the average-atom code Qaam which is based on the muffin-tin approximation. A disagreement between the eOCP and the actual PDFs (non-OCP behavior) is interpreted as the onset of bonding in the system.

DLITE—An inexpensive, deployable interferometer for solar radio burst observations

Solar radio bursts (SRBs) are brief periods of enhanced radio emission from the Sun. SRBs can provide unique insights into the plasma structure where emission occurs. SRBs can also provide critical information concerning space weather events such as coronal mass ejections or solar energetic particle events. Providing continuous monitoring of SRBs requires a full network of detectors continuously monitoring the Sun. A promising new network is being developed, employing a four-element interferometer called the Deployable Low-band Ionosphere and Transient Experiment (DLITE) array. DLITE, which operates in a 30–40 MHz band, was specifically designed to probe the Earth’s ionosphere using high resolution measurements (1.024-s temporal resolution, 16.276-kHz frequency resolution); however, this also makes DLITE a powerful new tool for providing detailed observations of SRBs at these frequencies. DLITE is particularly adept at detecting long-duration SRBs like Type II and Type IV bursts. DLITE provides high resolution SRB data that can complement ground-based networks like e-Callisto or space-based observations, e.g., from Wind/WAVES. As an inexpensive interferometer, DLITE has strong potential as an educational tool: DLITE can be used to study the ionosphere, SRBs, and even Jovian radio bursts. Future DLITE arrays could be enhanced by using the full 20–80 MHz band accessible by the antennas and employing its millisecond time-resolution capability; this would improve DLITE’s ability to track long-duration bursts, create the opportunity to study short-duration Type III bursts in detail, and, in particular, make the study of Type I bursts practical.

On the analytical and numerical approximations to the forced damped Gardner Kawahara equation and modeling the nonlinear structures in a collisional plasma

We perform a detailed study on the completely non-integrable forced damped Gardner/Extended Kawahara equation (FDEKE). Three techniques are introduced to determine abundance approximations to the proposed equation. In the first technique, the ansatz method is carried out for deriving some general formulas for the analytical approximations. In the second and third techniques, the FDEKE is analyzed numerically using both the septic B-spline collocation method and the method of lines. As a realistic model, the obtained approximations are employed for studying the properties of the periodic forced dissipative extended Kawahara solitary and cnoidal waves in a pair-ion plasma comprised of Maxwellian electrons and two fluid positive and negative ions. Both numerical and analytical approximations are graphically compared with each other. Also, the global maximum residual error L∞ for all obtained approximations is estimated for checking the accuracy of these approximations. Moreover, the obtained approximations can be applied for studying the features of the dissipative localized and periodic higher-order structures in optical fiber, ocean, sea, different models of plasma physics, and fluid mechanics.

Ion temperature gradient mode and its solitons with regularized κ-distributed electrons

The linear and the non-linear behaviors of the ion temperature gradient (ITG) mode in a plasma with regularized κ-distributed electrons are investigated using the fluid model. The dispersion relation of the ITG mode obtained on the basis of the local approximation shows that the growth rate of the ITG mode decreases with the increase in the spectral index κ and the exponential cut-off parameter α. It indicates that the presence of the superthermal electron leads to destabilization of the ITG mode, especially in the low κ (κ < 1.5) region. In addition, the existence and the nature of the soliton structure driven by the ITG are studied using the pseudopotential technology. The soliton amplitude increases with the increase in the exponential cut-off parameter α and the spectral index κ, whereas the width of the soliton varies inversely. The present results will help to understand the low-frequency electrostatic wave and nonlinear structure in space and experimental plasmas with non-thermal electrons.

Dynamics of He++ Ions at Interplanetary and Earth’s Bow Shocks

Experimental investigations of the fine plasma structure of interplanetary shocks are extremely difficult to conduct due to their small thickness and high speed relative to the spacecraft. We studied the variations in the parameters of twice-ionized helium ions (4He++ ions or α-particles) in the solar wind plasma during the passage of interplanetary shocks and Earth’s bow shock. We used data with high time resolution gathered by the BMSW (Bright Monitor of Solar Wind) instrument installed on the SPEKTR-R satellite, which operated between August 2011 and 2019. The MHD parameters of He++ ions (the bulk velocity Vα, temperature Tα, absolute density Nα, and helium abundance Nα/Np) are analyzed for 20 interplanetary shocks and compared with similar parameters for 25 Earth bow shock crossings. Measurements from the WIND, Cluster, and THEMIS satellites were also analyzed. The correlations in the changes in helium abundance Nα/Np with the parameters βi, θBn, and MMS were investigated. The following correlation between Nα/Np and the angle θBn was found: the lower the value of θBn, the greater the drop in helium abundance (Nα/Np) falls behind the IP shock front. For Earth’s bow shock crossings, we found a significant increase in the helium abundance (Nα/Np) in quasi-perpendicular events.

Foil explosion in megagauss magnetic fields: Non-uniform expansion and instabilities

This paper presents an analysis of the results of an experiment on the explosion of copper foils, which was carried out on the MIG generator that produced a current through the foil at a level of 2 MA with a current pulse rise time of 100 ns. The foil length (along the z axis) was 20 mm, width (along the x axis) 5 mm, and thickness (along the y axis) 250 μm. It was observed that when the foils were exploded in megagauss magnetic fields with the foil current flowing along the z axis, the expansion of the plasma was extremely nonisotropic. The expansion of the foil material along the x axis was suppressed, and it expanded only along the y axis. An analysis of the experimental data carried out using a radiation magnetohydrodynamic code has shown that the nonisotropy of the expansion was associated with an enhancement of the magnetic field at the narrow side of the foil. As a result of the field enhancement, the magnetic pressure at the narrow foil side significantly exceeded the magnetic pressure in the center of the foil surface. Using an HSFC Pro optical camera (providing a frame exposure time of 3 ns), large-scale instabilities with wavelengths of 0.2–0.5 mm were detected on the foil surface. In appearance, these instabilities were similar to those developing in an exploding rod. It was suggested that the most likely cause of the appearance of the plasma structure observed in the experiment was the growth of flute instabilities.

Variations of He++ Ion Parameters at Interplanetary and Earth’s Bow Shock Fronts

Experimental investigations of the fine plasma structure of interplanetary shocks are extremely difficult to conduct due to their small thickness and high speed relative to the spacecraft. We study the variations in the parameters of twice-ionized helium ions (4He++ ions or {\alpha}-particles) in the solar wind plasma during the passage of interplanetary shocks and Earth's bow shock. We use data with high time resolution gathered by the BMSW (Bright Monitor of Solar Wind) instrument installed on the SPEKTR-R satellite, which operated between August 2011 and 2019. The MHD parameters of He++ ions (the bulk velocity Va, temperature Ta, absolute density Na, and helium abundance Na/Np) are analyzed for 20 interplanetary shocks and compared with similar parameters for 25 Earth's bow shock crossings. Measurements from the WIND, Cluster and THEMIS satellites were also analyzed. The correlations in the changes in helium abundance Na/Np with the parameters {\beta}_{i}, {\theta}_{Bn} and M_{ms} were investigated. A correlation between Na/Np and the angle {\theta}_{Bn} was found: the lower the value of {\theta}_{Bn}, the greater the drop in helium abundance Na/Np falls behind the IP shock front. For Earth's bow shock crossings, we found a significant increase in the helium abundance Na/Np in quasi-perpendicular events.

Male mice engaging differently in emotional eating present distinct plasmatic and neurological profiles

ABSTRACT Objective: Stressed individuals tend to turn to calorie-rich food, also known as ‘comfort food’ for the temporary relief it provides. The emotional eating drive is highly variable among subjects. Using a rodent model, we explored the plasmatic and neurobiological differences between ‘high and low emotional eaters’ (HEE and LEE). Methods: 40 male mice were exposed for 5 weeks to a protocol of unpredictable chronic mild stress. Every 3 or 4 days, they were submitted to a 1-h restraint stress, immediately followed by a 3-h period during which a choice between chow and chocolate sweet cereals was proposed. The dietary intake was measured by weighing. Plasmatic and neurobiological characteristics were compared in mice displaying high vs low intakes. Results: Out of 40 mice, 8 were considered as HEE because of their high post-stress eating score, and 8 as LEE because of their consistent low intake. LEE displayed higher plasma corticosterone and lower levels of NPY than HEE, but acylated and total ghrelin were similar in both groups. In the brain, the abundance of NPY neurons in the arcuate nucleus of the hypothalamus was similar in both groups, but was higher in the ventral hippocampus and the basal lateral amygdala of LEE. The lateral hypothalamus LEE had also more orexin (OX) positive neurons. Both NPY and OX are orexigenic peptides and mood regulators. Discussion: Emotional eating difference was reflected in plasma and brain structures implicated in emotion and eating regulation. These results concur with the psychological side of food consumption.

Achieving tunable Kerker-type invisibility for a radiation-enhanced electrically small antenna.

Low-temperature gaseous plasmas exhibit great potential in designing tunable and reconfigurable electromagnetic devices. In this paper, based on an overdense-underdense core-shell plasma structure, tunable Kerker-type invisibility for a radiation-enhanced electrically small antenna is achieved, where dominant scattering direction can be mutated between backward and forward while omnidirectional invisibility and signal enhancement are maintained. Moreover, by electromagnetic multipole decompositions, it is shown that the underdense outer plasma with a negative polarizability is able to weaken the strength and modulate the phase of the electric dipolar scattering component (a_{1}), while the magnetic dipolar term (b_{1}) nearly remains unchanged. Consequently, quasi-first and -second Kerker conditions are fulfilled near the cutoff band of a_{1}.

Ion-acoustic nonlinear structures in a non-Maxwellian plasma in the presence of an electron beam

Ion-acoustic nonlinear structures in a non-Maxwellian plasma in the presence of an electron beam

Superlubric-pinned transition of a two-dimensional solid dusty plasma under a periodic triangular substrate.

The superlubric-pinned transition in the depinning dynamics of a two-dimensional (2D) solid dusty plasma modulated by 2D triangular periodic substrates is investigated using Langevin dynamical simulations. When the lattice structure of the 2D solid dusty plasma perfectly matches the triangular substrate, two distinctive pinned and moving ordered states are observed as the external uniform driving force gradually increases from zero. When there is a mismatch between the lattice structure and the triangular substrate, however, on shallow substrates, it is discovered that all of the particles can slide freely on the substrate even when the applied driving force is tiny. This is a typical example of superlubricity, which is caused by the competition between the substrate-particle and particle-particle interactions. If the substrate depth increases further, as the driving force increases from zero, there are three dynamical states consisting of the pinned state, the disordered plastic flow state, and the moving ordered state. In an underdense system, where there are fewer particles than potential well minima, it is found that the occurrence of the three different dynamical states is controlled by the depth of the substrate, which is quantitatively characterized using the average mobility.