Plasma Compression Research Articles

A Multifrequency View of the Radio Phoenix in the A85 Cluster

Radio phoenices are complex and filamentary diffuse radio sources found in both merging and relaxed clusters. The formation of these sources has been proposed to be due to adiabatic compression of old active galactic nucleus plasma in shock waves. Most of the previous spectral studies of these sources have been limited to integrated spectral indices, which were found to be very steep and show a curved spectrum. Here, we have performed a multifrequency investigation of the radio phoenix in the A85 cluster. Owing to the sensitive high-resolution observations, we found some of the finer filamentary structures that had been previously undetected. We produced resolved spectral index maps of the radio phoenix between 323, 700, and 1280 MHz. The orientation of the filaments, as well as the gradient across the spectral index maps, suggest the possible direction of the shock motion from northeast to southwest. The integrated spectrum of the radio phoenix was found to be very steep and curved toward high frequencies. Furthermore, the spectral index of the filaments was found to be less steep compared to the nonfilamentary regions, implying greater energy injection in the filaments. The observed features in the radio phoenix in the A85 cluster seem to be in support of an adiabatic shock compression mechanism.

An implicit particle code with exact energy and charge conservation for studies of dense plasmas in axisymmetric geometries

A collisional particle code based on implicit energy- and charge-conserving methods in axisymmetric geometries is presented. A new particle pusher for axisymmetric systems is introduced that is compatible with exact energy and charge conservation and yields improved accuracy compared to other methods. How to appropriately treat all aspects of the algorithm near the r=0 axis of symmetry is described in detail. The axisymmetric model is verified by simulating the free expansion of a plasma sphere in 2D cylindrical and 1D spherical geometries. The algorithm's ability to study the dynamic compression of a dense plasma is illustrated by simulating the dynamic Z-pinch in 1D cylindrical geometry.

Energetic Electrons Accelerated and Trapped in a Magnetic Bottle above a Solar Flare Arcade

Where and how flares efficiently accelerate charged particles remains an unresolved question. Recent studies revealed that a “magnetic bottle” structure, which forms near the bottom of a large-scale reconnection current sheet above the flare arcade, is an excellent candidate for confining and accelerating charged particles. However, further understanding its role requires linking the various observational signatures to the underlying coupled plasma and particle processes. Here we present the first study combining multiwavelength observations with data-informed macroscopic magnetohydrodynamics and particle modeling in a realistic eruptive flare geometry. The presence of an above-the-loop-top magnetic bottle structure is strongly supported by the observations, which feature not only a local minimum of magnetic field strength but also abruptly slowing plasma downflows. It also coincides with a compact above-the-loop-top hard X-ray source and an extended microwave source that bestrides the flare arcade. Spatially resolved spectral analysis suggests that nonthermal electrons are highly concentrated in this region. Our model returns synthetic emission signatures that are well matched to the observations. The results suggest that the energetic electrons are strongly trapped in the magnetic bottle region due to turbulence, with only a small fraction managing to escape. The electrons are primarily accelerated by plasma compression and facilitated by a fast-mode termination shock via the Fermi mechanism. Our results provide concrete support for the magnetic bottle as the primary electron acceleration site in eruptive solar flares. They also offer new insights into understanding the previously reported small population of flare-accelerated electrons entering interplanetary space.

Investigation on the Structural and Mechanical Properties of Al Foam Manufactured by Spark Plasma Sintering and Compression Molding Methods

Investigation on the Structural and Mechanical Properties of Al Foam Manufactured by Spark Plasma Sintering and Compression Molding Methods

Plasma compressibility and the generation of electrostatic electron Kelvin–Helmholtz instability

This study explores the generation of electrostatic (ES) electron Kelvin–Helmholtz instability (EKHI) in collisionless plasma with a step-function electron velocity shear akin to that developed in the electron diffusion region in magnetic reconnection. In incompressible plasma, ES EKHI does not arise in any velocity shear profile due to the decoupling of the electric potential from the electron momentum equation. Instead, a fluid-like Kelvin–Helmholtz instability (KHI) can arise. However, in compressible plasma, the compressibility couples the electric potential with the electron dynamics, leading to the emergence of a new ES mode EKHI on Debye length λDe, accompanied by the co-generation of an electron acoustic-like wave. The minimum threshold of ES EKHI is ΔU>2cse, i.e., the electron velocity shear is larger than twice the electron acoustic speed cse. The corresponding growth rate is Im(ω)=((ΔU/cse)2−4)1/2ωpe, where ωpe is the electron plasma frequency.

Compression and acceleration of ions by ultrashort, ultraintense azimuthally polarized light.

An efficient plasma compression scheme using azimuthally polarized light is proposed. Azimuthally polarized light possesses a donutlike intensity pattern, enabling it to compress and accelerate ions toward the optical axis across a wide range of parameters. When the light intensity reaches the relativistic regime of 10^{18}W/cm^{2}, and the plasma density is below the critical density, protons can be compressed and accelerated by the toroidal soliton formed by the light. The expansion process of the soliton can be well described by the snowplow model. Three-dimensional particle-in-cell simulations show that within the soliton regime, despite the ion density exceeding ten times the critical density, the ions' energy is insufficient for efficient neutron production. When the light intensity increases to 10^{22}W/cm^{2}, and the plasma density reaches several tens of times the critical density, deuterium ions can be compressed to thousands of times the critical density and simultaneously accelerated to the MeV level by tightly focused azimuthally polarized light during the hole-boring process. This process is far more dramatic compared to the soliton regime and can produce up to 10^{4} neutrons in a few light cycles. Moreover, in the subsequent beam-target stage, neutron yield is estimated to exceed 10^{8}. Finally, we present a comparison with the results obtained using a radially polarized light to examine the influence of light polarization.

On the Heating of the Slow Solar Wind by Imbalanced Alfvén-wave Turbulence from 0.06 to 1 au: Parker Solar Probe and Solar Orbiter Observations

In this work we analyze plasma and magnetic field data provided by the Parker Solar Probe and Solar Orbiter missions to investigate the radial evolution of the heating of Alfvénic slow wind by imbalanced Alfvén-wave (AW) turbulent fluctuations from 0.06 to 1 au. in our analysis we focus on slow solar-wind intervals with highly imbalanced and incompressible turbulence (i.e., magnetic compressibility C B = δ B/B ≤ 0.25, plasma compressibility C n = δ n/n ≤ 0.25, and normalized cross helicity σ c ≥ 0.65). First, we estimate the AW turbulent dissipation rate from the wave energy equation and find that the radial profile trend is similar to the proton heating rate. Second, we find that the scaling of the empirical AW turbulent dissipation rate Q W obtained from the wave energy equation matches the scaling from the phenomenological AW turbulent dissipation rate Q CH09 (with Q CH09 ≃ 1.55Q W ) derived by Chandran & Hollweg based on the model of reflection-driven turbulence. Our results suggest that, as in the fast solar wind, AW turbulence plays a major role in the ion heating that occurs in incompressible slow-wind streams.

Estimation of negative membrane tension in lipid bilayers and its effect on antimicrobial peptide magainin 2-induced pore formation.

Positive membrane tension in the stretched plasma membrane of cells and in the stretched lipid bilayer of vesicles has been well analyzed quantitatively, whereas there is limited quantitative information on negative membrane tension in compressed plasma membranes and lipid bilayers. Here, we examined negative membrane tension quantitatively. First, we developed a theory to describe negative membrane tension by analyzing the free energy of lipid bilayers to obtain a theoretical equation for negative membrane tension. This allowed us to obtain an equation describing the negative membrane tension (σosm) for giant unilamellar vesicles (GUVs) in hypertonic solutions due to negative osmotic pressure (Π). Then, we experimentally estimated the negative membrane tension for GUVs in hypertonic solutions by measuring the rate constant (kr) of rupture of the GUVs induced by the constant tension (σex) due to an external force as a function of σex. We found that larger σex values were required to induce the rupture of GUVs under negative Π compared with GUVs in isotonic solution and quantitatively determined the negative membrane tension induced by Π (σosm) by the difference between these σex values. At small negative Π, the experimental values of negative σosm agree with their theoretical values within experimental error, but as negative Π increases, the deviation increases. Negative tension increased the stability of GUVs because higher tensions were required for GUV rupture, and the rate constant of antimicrobial peptide magainin 2-induced pore formation decreased.

Planar shock compression of spark plasma sintered B4C and B4C–TiB2 ceramic composites

Blending of ceramic constituent phases enhances sinterability and performance in high strength ceramics. Here, a near fully dense blended boron carbide (B4C)–titanium diboride (TiB2) composite produced through spark plasma sintering (SPS) is probed to understand the mechanical performance under dynamic uniaxial strain, or shock compression. This study on the shock performance of blended B4C–TiB2 measures the effect of initial TiB2 powder size on the dynamic response of the composite and compares results to those of monolithic SPS B4C. These shock experiments reveal a strengthening of the Hugoniot elastic limit (HEL) with an addition of TiB2 and mitigation of the adverse post-HEL response observed in many brittle ceramics, such as monolithic B4C. The TiB2 particle size in the composite does not noticeably influence these results. The tough nature of TiB2 along with compressive residual stresses in the B4C matrix resulting from high temperature processing and a mismatch of the thermal expansion coefficients of the constituent phases are postulated to strengthen the B4C.

Resistive instabilities in toroidal anisotropic plasmas

Resistive singular layer equations are developed by applying the magnetohydrodynamic (MHD) model to toroidal anisotropic plasmas. This work extends the previous ideal MHD theory [Shi et al. Phys. Plasmas 23, 082121 (2016)] to the resistive case. These layer equations can be used to investigate resistive localized MHD instabilities, such as tearing instability and resistive interchange instability. Compared to existing resistive theory [Johnson and Hastie, Phys. Fluids 31, 1609 (1988)], our model includes plasma compressibility, allowing for a study of the coupling between parallel motion to perpendicular one, which is known as the apparent mass effect. In addition, these obtained equations are valid for low n modes, where n is the toroidal mode number. The dispersion relation is derived in a reduced model. We find that the anisotropic pressure effect (when p⊥ > p‖) not only increases the stable threshold of the resistive interchange mode but also raises the critical value Δc of the tearing mode stability index Δ′, which represents the logarithmic jump of the radial magnetic field perturbation across the rational surface. This discovery holds significant practical implications for mitigating neoclassical tearing modes in high confinement plasmas, particularly those characterized by a low aspect ratio (such as spherical tokamaks) or low magnetic shear (as designed in ITER hybrid scenarios). However, it enhances the growth rate of the tearing mode in a low growth rate region, where p‖ and p⊥ denote the pressure components parallel and perpendicular to the magnetic fields, respectively.

Surface Degradation of Thin-Layer Al/MgF2 Mirrors under Exposure to Powerful VUV Radiation.

Thin-layer Al/MgF2 coatings are currently used for extraterrestrial far-UV astronomy as the primary and secondary mirrors of telescopes (such as "Spektr-UF"). Successful Hubble far-UV measurements have been performed thanks to MgF2 on Al mirror coatings. Damage of such thin-layer coatings has been previously studied under exposure to high-energy electrons/protons fluxes and in low Earth orbit environments. Meanwhile, there is an interest to test the stability of such mirrors under the impact of extreme radiation fluxes from pulsed plasma thrusters as a simulation of emergency onboard situations and other applications. In the present studies, the high current and compressed plasma jets were generated by a laboratory plasma thruster prototype and operated as effective emitters of high brightness (with an integral overall wavelength radiation flux of >1 MW/cm2) and broadband radiation. The spectrum rearrangement and hard-photon cut-off at energy above Ec were implemented by selection of a background gas in the discharge chamber. The discharges in air (Ec ≈ 6 eV), argon (Ec ≈ 15 eV) and neon (Ec ≈ 21 eV) were studied. X-ray diffraction and reflectometry, electron and atomic force microscopy, and IR and visible spectroscopy were used for coating characterization and estimation of degradation degree. In the case of the discharges in air with photon energies of E < 6 eV, only individual nanocracks were found and property changes were negligible. In the case of inert gases, the energy fraction was ≈50% in the VUV range. As found for inert background gases, an emission of such hard photons with energies higher than the MgF2 band gap energy of ≈10.8 eV caused a drastic light-induced ablation and degradation of the irradiated coatings. The upward trend of degradation with an increasing of the maximum photon energies was detected. The obtained data on the surface destruction are useful for the design of methods for coating stability tests and an understanding of the consequences of emergencies onboard space research stations.

Total neutron emission from deuteron fusion and plasma pinch compression in a medium-sized plasma focus operating with D2 and D2 + Ne gas mixtures—Experimental results

Newly obtained results on hot and dense deuterium and deuterium-neon plasma compression in a z-pinch electrical discharge configuration are presented. The investigated plasma was generated and compressed using 269 high-current discharges in a medium-sized (dense) plasma focus device. The experimental chamber of the device was filled with deuterium and deuterium-neon gas mixtures under constant total mass/density conditions. Magnetic and electric probes, beryllium neutron activation counter, and high-speed four-frame vacuum ultraviolet/soft x-ray pinhole camera were used to study the plasma dynamics and radiation emission. The results obtained experimentally for the first time confirmed clearly a decrease in the minimum radius of plasma columns with an increase in initial neon fraction. Simultaneously, a decrease in the total neutron emission from deuteron fusion was found. The observed plasma/discharge evolution revealed that the classical description of plasma-focus discharges can be approximately correct up to the moment of maximum compression. Including, existence of quasi-equilibrium plasma compression is probable. It is also possible that the homogeneity of plasma columns during the slow compression phase and maximum compression moment increases with the increase in initial neon fraction. The effect of higher stabilization (repeatability) of discharges was confirmed, for higher initial neon fractions. The dependency of the total neutron emission yield on the parameters describing the full discharge dynamics and the maximum discharge voltage was confirmed. The existence of this type of dependency, for a minimum pinch radius is also possible. In contrast, there was little dependency to the total discharge current parameters measured in the collector area.

Adiabatic energy change in the inner heliosheath: how does it affect the distribution of pickup protons and energetic neutral atom fluxes?

ABSTRACT The hydrogen atoms penetrate the heliosphere from the local interstellar medium, and while being ionized, they form the population of pickup protons. The distribution of pickup protons is modified by the adiabatic heating (cooling) induced by the solar wind plasma compression (expansion). In this study, we emphasize the importance of the adiabatic energy change in the inner heliosheath that is usually either neglected or considered improperly. The effect of this process on the energy and spatial distributions of pickup protons and energetic neutral atoms (ENAs), which originate in the charge exchange of pickup protons, has been investigated and quantified using a kinetic model. The model employs the global distributions of plasma and hydrogen atoms in the heliosphere from the simulations of a kinetic-magnetohydrodynamic model of solar wind interaction with the local interstellar medium. The findings indicate that the adiabatic energy change is responsible for the broadening of the pickup proton velocity distribution and the significant enhancement of ENA fluxes (up to ∼5 and ∼20 times in the upwind and downwind directions at energies ∼1–2 keV for an observer at 1 au). It sheds light on the role of adiabatic energy change in explaining the discrepancies between the ENA flux observations and the results of numerical simulations.

Interstellar Conditions Deduced from Interstellar Neutral Helium Observed by IBEX and Global Heliosphere Modeling

In situ observations of interstellar neutral (ISN) helium atoms by the IBEX-Lo instrument on board the Interstellar Boundary Explorer (IBEX) mission are used to determine the velocity and temperature of the pristine very local interstellar medium (VLISM). Most ISN helium atoms penetrating the heliosphere, known as the primary population, originate in the pristine VLISM. As the primary atoms travel through the outer heliosheath, they charge exchange with He+ ions in slowed and compressed plasma, creating the secondary population. With more than 2.4 million ISN helium atoms being sampled by IBEX during ISN seasons 2009–2020, we compare the observations with the predictions of a parameterized model of ISN helium transport in the heliosphere. We account for the filtration of ISN helium atoms at the heliospheric boundaries by charge-exchange and elastic collisions. We examine the sensitivity of the ISN helium fluxes to the interstellar conditions described by the pristine VLISM velocity, temperature, magnetic field, and composition. We show that comprehensive modeling of the filtration processes is critical for interpreting ISN helium observations, as the change in the derived VLISM conditions exceeds the statistical uncertainties when accounting for these effects. The pristine VLISM parameters found by this analysis are the flow speed (26.6 km s−1), inflow direction in ecliptic coordinates (255.°7, 5.°04), temperature (7350 K), and B − V plane inclination to the ecliptic plane (53.°7). The derived pristine VLISM He+ density is 9.7 × 10−3 cm−3. Additionally, we show a strong correlation between the interstellar plasma density and magnetic field strength deduced from these observations.

A kinetic model for pure electron plasma compression via the rotating wall technique

An approximate model for pure electron plasma compression is developed for the case where the rotating wall (RW) electric field couples to the $E\times B$ rotation and axial bounce motion of the electrons. The key assumption in the model is that, throughout the compression, the plasma remains in a slowly evolving thermal equilibrium defined by the plasma temperature and angular momentum. Linearized drift kinetic theory is employed to derive an expression for torque exerted by the RW field on the plasma through coupling to the resonant plasma particles, and averaging is used to find the torque that both compresses and heats the plasma. The evolution equations for the angular velocity and temperature of the plasma include the compression and heating from the torque and cooling from cyclotron radiation.

Fundamental Scaling of Adiabatic Compression of Field Reversed Configuration Thermonuclear Fusion Plasmas

Field Reversed Configuration (FRC) plasmas are plasma devices that have demonstrated that through magnetic compression they can be heated to thermonuclear fusion conditions in the parameter space of an energy-producing generator Kirtley et al. (IEEE Symposium on Fusion Engineering, 2021). Of particular interest, FRCs are high-beta, in that the plasma particle kinetic energy is in balance with an externally applied magnetic field at all stages of operation. The following work will show that a cylindrical approximation for the energy and particle distribution within an FRC can, within 11%, match the fusion performance results of both full Magnetohydrodynamic (MHD) simulations as well as all robust, modern theoretical spatial and energy distribution models. Further, by using the simplified cylindrical model, detailed fusion reaction, radiation, and energy transport equations are now numerically-tractable and can be modelled over a wide parameter space. In the second section of this work, a detailed numerical model will be presented with the key theoretical performance of the compression of high-beta fusion plasmas in both deuterium–tritium (D–T) and deuterium–helium-3 (D–He-3) fuels. As will be shown, a high-beta D–He-3 plasma outperforms a low-beta D–T fuel and can theoretically yield a net-positive fusion generator.

On the Possibility of Achieving Thermonuclear Ignition During Magnetic Compression of High-Temperature Magnetized Plasma by the Current of a Disk Explosive Magnetic Generator

One of the directions for achieving thermonuclear ignition is compression of a heated, magnetized plasma by a liner. This concept was developed in the USA at the Z Machine (MagLIF project). To achieve ignition, it is necessary to create a current pulse with an amplitude of 60 MA or higher. The Z Machine produces currents with amplitudes up to 25 MA. The development of more powerful installations is a problem for the future. At the same time, today already, the explosive magnetic generators create the required currents with long current rise times. In this work, based on calculation results of the compression of a hot magnetized plasma, the possibilities of achieving ignition using modern disc explosive magnetic generators are discussed.

Interplanetary Shocks between 0.3 and 1.0 au: Helios 1 and 2 Observations

The Helios 1 (H1) and Helios 2 (H2) spacecraft measured the solar winds at a distance between ∼0.3 and 1.0 au from the Sun. With increasing heliocentric distance (r h), the plasma speed is found to increase at ∼34–40 km s−1 au−1 and the density exhibits a sharper fall () compared to the magnetic field magnitude () and the temperature (). Using all available solar wind plasma and magnetic field measurements, we identified 68 and 39 fast interplanetary shocks encountered by H1 and H2, respectively. The overwhelming majority (85%) of the shocks are found to be driven by interplanetary coronal mass ejections (ICMEs). While the two spacecraft encountered more than 73 solar wind high-speed streams (HSSs), only ∼22% had shocks at the boundaries of corotating interaction regions (CIRs) formed by the HSSs. All of the ICME shocks were found to be fast forward (FF) shocks; only four of the CIR shocks were fast reverse shocks. Among all ICME FF shocks (CIR FF shocks), 60% (75%) are quasi-perpendicular with shock normal angles (θ Bn) ≥ 45° relative to the upstream ambient magnetic field, and 40% (25%) are quasi-parallel (θ Bn < 45°). No radial dependences were found in FF shock normal angle and speed. The FF shock Mach number (M ms), magnetic field, and plasma compression ratios are found to increase with increasing r h at the rates of 0.72, 0.89, and 0.98 au−1, respectively. On average, ICME FF shocks are found to be considerably faster (∼20%) and stronger (with ∼28% higher M ms) than CIR FF shocks.

Slipping instability of an inhomogeneous relativistic electron beam

The charged particle beams, such as electrons, ions, and plasma compression flow, have received considerable attention due to their applications in science and technology; therefore, studying the stability of these beams is of particular importance. Here, we examine theoretically the stability properties of a cold relativistic electron beam with a transverse velocity shear and non-uniform density profile. We consider a plane-parallel beam propagating along an external magnetic field and evaluate its macroscopic equilibrium state. We derive the dispersion relation of the slipping instability based on the linear electrodynamics of an inhomogeneous plasma and kinetic theory. In this model, the oscillation spectrum and the growth rate are derived by using the eikonal equation and the quasi-classical quantization rule. A linear velocity shear and a non-linear density gradient are assumed. Furthermore, we analyze numerically the dispersion relation of the slipping instability. The impacts of the inhomogeneity parameter and the relativistic factor on the properties of the slipping instability are discussed.

Experimental and simulation studies on damage mechanisms of tungsten and molybdenum under compressed plasma flow irradiation

The failure mechanism of plasma-facing components (PFCs) under extreme plasma conditions relevant for fusion reactors were investigated. Here, edge-localized mode (ELM)-like transient thermal shock irradiation experiments were performed on tungsten and molybdenum using compressed plasma flow, and combined with thermal–mechanical analysis by means of finite element simulations to discuss the grain structure evolution, cracking behavior and variations of hardness. When ELM-like thermal shock irradiation was sufficient to melt tungsten and molybdenum, a submicron-sized cellular sub-grain structure was created on their surface due to the high temperature gradient of the molten layer under the effect of Bénard–Marangoni instability. Rapid directional solidification from the bottom of the molten layer to the surface induced the formation of columnar grains dominated by the <200> orientation. While the formation of cellular sub-grains increased hardness, the thermal effect of irradiation and the formation of columnar grains led to softening. The high thermal stress induced by the ELM-like thermal shock produced macro-cracks and micro-cracks on the surface of tungsten and only micro-cracks on the surface of molybdenum. Macro-cracks were generated due to the intrinsic brittleness of tungsten. As a result of stress evolution, longitudinal macro-cracks extending perpendicular to the surface experienced transverse transformation within the material. Micro-cracks formed due to the embrittlement of the re-solidification zone, and their width increased with the melting depth. These results help us to understand failure mechanisms in PFCs under extreme operating conditions and are valuable for developing future fusion reactors.