Plasma Interaction Research Articles

Asymmetric Complex Plasma Interaction Energy in the Poisson–Boltzmann Plus Hole Approximation

Asymmetric Complex Plasma Interaction Energy in the Poisson–Boltzmann Plus Hole Approximation

A reduced-model (nSOLT) simulation of neutral recycling effects on plasma turbulence in the divertor region of MAST-U

The 2D scrape-off-layer turbulence code (nSOLT), which includes 1D kinetic neutral–plasma interactions, is applied to study effects of neutral recycling on plasma turbulence for parameters illustrative of the MAST-U divertor region. Neutral recycling is modeled by injecting a fraction of the parallel plasma flux to the divertor back into the simulation domain as a source of Franck–Condon-distributed neutrals. Stationary sources, concentrated at the magnetic separatrix, model plasma streaming into the divertor region from the upstream scrape-off-layer and sustain plasma turbulence absent neutral recycling. Starting from one such no-neutrals equilibrium, we initiate recycling in a numerical experiment designed to diagnose and identify the effects of various neutral–plasma interactions on the divertor plasma, divertor turbulence, and plasma exhaust. The onset of recycling triggers an initial burst of enhanced cross field plasma transport that is quelled by ionization cooling and charge–exchange (CX) friction, with growing neutral pressure, leading to a quiescent, turbulence-free state. Diagnosis of this transient burst reveals that (1) the sudden increase in plasma density due to ionization dominates the onset of the burst, (2) electron cooling due to ionization increases collisionality and disconnects blob filaments from the sheath, and (3) CX friction drives tripole polarization of a blob that can dominate the curvature-driven dipole polarization, leading to the stagnation of blob propagation and reduced radial turbulent transport. It is shown that CX friction is negligible compared to sheath physics in determining equilibrium mean flow shearing rates, for parameters considered herein (specifically a short connection length to the divertor target), while it can significantly reduce interchange-instability growth rates.

Enhancement of guided electromagnetic wave by pre-plasma formation in laser–plasma interaction

Previous studies have shown that adding a section of critical density plasma on the front surface of solid target can effectively improve the laser energy absorption efficiency. Here, we have investigated laser–plasma interactions with different scale lengths of plasma in front of the target created by a pre-ablation laser pulse. A variety of experimental diagnostics employed together with particle-in-cell simulations give us deep insight into these processes. We found that the laser-induced electromagnetic pulse (EMP) intensity inside the target chamber and the target normal sheath acceleration sheath field accelerated protons were promoted using pre-plasma. The transient current due to hot electron emissions is considered to be one of the main radiation sources of EMP emissions within our measurement bandwidth. In our experiment, this current was guided to a grounded conductive wire attached to the rear surface of the target and measured by proton dynamic imaging technique. The discharging currents together with the guided fields were enhanced more than twice. The reflection spectra of experiments and simulations are compared, which reveal that the energy absorption efficiency was increased with proper plasma scale length, resulting in all the measured signals promoted.

Solar Electron Beam Velocities That Grow Langmuir Waves in the Inner Heliosphere

Solar accelerated electron beams, a component of space weather, are emitted by eruptive events at the Sun. They interact with the ambient plasma to grow Langmuir waves, which subsequently produce radio emission, changing the electrons’ motion through space. Solar electron beam–plasma interactions are simulated using a quasilinear approach to kinetic theory to probe the variations in the maximum electron velocity [Xi ] responsible for Langmuir wave growth between the Sun’s surface and 50 R⊙ above the surface. We find that it peaks at 5 R⊙ at 0.38 c and decreases as r^{-0.5} to 0.16 c at 50 R⊙. The role of the initial beam density [n_{mathrm{beam}}] and velocity spectral index [alpha ] on the energy density of the beam and Xi is extensively studied. We show that a high spectral index yields a lower Xi , while a high n_{mathrm{beam}} yields a higher Xi , and vice versa. We observe at different energy channels that below 60 keV, electrons arrive up to 0.75 minutes earlier than expected at 13 R⊙ while higher energy electrons propagate scatter free in the plasma. A special focus on the associated Type III radio burst shows that the energy range [Delta E] of electrons producing Langmuir waves evolves from 7 keV to 1 keV between 0 and 28 R⊙. Understanding the transport effect on the electron beam kinetics and arrival time at Earth has space weather implications. The results of this simulation can be tested against readily available in-situ data from Solar Orbiter and Parker Solar Probe.

On a modified Korteweg–de Vries equation for electrostatic structures in relativistic degenerate electron–positron plasma

In this paper, the propagation of acoustic solitons in an electron–positron (e–p) degenerate plasma with the relativistically degenerate electrons and positrons is studied. Moreover, we considered stationary positive ions for neutralizing the plasma background. Using the reductive perturbation method, we obtained a modified Korteweg–de Vries equation. By applying a Jacobi elliptic function expansion method, we have proposed the exact analytical solitary, kink, and periodic solutions for the nonlinear wave structures. Also, using the phase plane analysis three equilibrium points have been perceived two of them should be centers and the last is a saddle for quantum acoustic waves. The numerical and computational results show that firstly some of them should be discarded by physical values and then these solutions have been influenced by the plasma parameters such as the electron degenerate density parameter (ne0) and the ion-to-electron density ratio (δ) which peaked out in white dwarf stars. It is found that both the amplitude and the width of the nonlinear structures are affected by the mentioned parameters. This investigation is useful for the relativistically degenerate plasma media in ultra-dense astrophysical environments (such as neutron stars, white dwarfs, etc.), inertia fusion science, experiments involving the interaction of laser and solid density plasma, and inertial confinement fusion in which the relativistic effects play a major role.

Applications of Non-linear Inverse Compton Scattering based on the Laser Plasma Accelerators

The generation of energetic photons in the context of inverse Compton scattering has attracted a great lot of interest from many contemporary scientific fields. Radiobiology, materials physics, and medicine are some of the current fields where inverse Compton scattering is used. In this study, the applications of nonlinear inverse Compton scattering will be demonstrated and illustrated based on laser plasma interaction. This paper introduces and highlights the current advancement in this area, which is a crucial component of quantum physics, as well as the potential uses in the future depending on additional study. Thorough explanations are demonstrated and talked about the uses of inverse Compton scattering. To highlight our thoughts on present developments and potential future advancements in the field, we have extended and expanded on the theme using simulations and experimental data. These results pave a path to generate and shed light on guiding further state-of-art proposals for High flux X/gamma ray generation.

Study of plasma sheath in the presence of dust particles in a magnetic mirror-like field configuration

The properties of a plasma sheath in the presence of dust grains and a magnetic mirror-like field configuration have been investigated in this study. All the plasma species viz. electrons, ions, and dust grains are described by fluid equations. The system of equations involved in the study is solved numerically using the Runge-Kutta fourth-order (RK4) method to explore the sheath properties. The results of the study suggest that in the presence of a magnetic mirror-like field configuration, the component of ion velocity perpendicular to the wall decreases near the surface, and consequently, the ion density increases. To the best of our knowledge, such observations have not been reported anywhere previously. This utterly different observation is due to the magnetic field configuration alone. Such a behavior can be used to control the dynamics of the ions in the sheath. Moreover, ion-neutral collisions tend to reduce the effect of the magnetic field on the properties of the sheath. The study may be helpful to understand the interactions of plasma with the wall in different plasma-assisted industrial applications containing dust grains as contaminants. Besides, the study will play a significant role in controlling the dynamics of positive ions and negatively charged dust grains in the sheath. The space charge shows an unusual behavior near the sheath. In the usual scenario, the space charge slightly decreases near the wall. But in the present context, the space charge increases. Further, it has been observed that the dust surface potential near the wall becomes less negative with the increase in magnetic field strength. The magnetic field and ion-neutral collisions tend to restrict the movement of the ions toward the wall when acting separately, but their combined effect leads to a different kind of behavior altogether.

Time‐dependent charged particle stopping in quantum plasmas: testing the G1–G2 scheme for quasi‐one‐dimensional systems

AbstractWarm dense matter—an exotic, highly compressed state on the border between solid and plasma phases is of high current interest, in particular for compact astrophysical objects, high‐pressure laboratory systems, and inertial confinement fusion. For many applications, the interaction of quantum plasmas with energetic particles is crucial. Moreover, often the system is driven far out of equilibrium. In that case, there is high interest in time‐dependent simulations to understand the physics, in particular, during thermalization. Recently a novel many‐particle technique, the G1–G2 scheme was presented with reference to the study by Schlünzen et al. (2020) which allows for first‐principle simulations of the time evolution of interacting quantum systems. Here we apply this scheme to a spatially uniform dense quantum plasma (jellium) and explore its performance. To this end, the G1–G2 scheme is transformed into momentum representation, and first results are presented for a quasi‐one‐dimensional model system.

Theoretical investigation of the interaction of ultra-high intensity laser pulses with near critical density plasmas

A theoretical model of energy transfer from laser to particles in the ultra-high intensity regime of laser plasma interaction is proposed, assuming that most of the laser energy will be transferred to hot electrons. Varying the target density and thickness, the optimal parameters for the maximum conversion efficiency of the laser energy to particles are studied. Through 2D particle-in-cell simulations, the model is validated for a near-critical density plasma between (where cm−3 is the critical density for a laser wavelength of m) irradiated by a laser pulse of intensity in the range 1020–1023 W cm−2 and the pulse duration in the range 6.5–100 fs. As an application to this model, laser ion acceleration is studied for a laser intensity of 1022 W cm−2 and a pulse duration of 20 fs. Based on the literature and new findings from our model, the optimum thickness for ion acceleration and the maximum ion energies for an expansion like mechanism are predicted. These results can be used for applications requiring high energy ions and for preparations of experiments at the Apollon and ELI laser facilities.

Temporal evolution of pressure profiles for laser-induced cavitation bubble on the metal surface

When a laser is focused on an underwater object, it experiences a large amount of pressure owing to the plasma confinement effect of water. A hemispherical bubble is generated on the surface of the object, and large pressure is generated when the bubble collapses. In this study, we conducted experiments using different laser energies to analyze the pressure–time histories associated with bubble contraction. The maximum pressure was 10%–40% of the laser ablation pressure, whereas the pressure pulse width was 5–10 times longer than the laser pulse width. Furthermore, the bubble motion could be adiabatically explained, except for the plasma interaction region. The results indicate that the pressure at which the bubble collapses does not depend on the maximum size of the generated bubble but depends on the energy of water vapor within the bubble.

Outside Front Cover: Plasma Process. Polym. 3/2023

Outside Front Cover: Peptides undergo chemical modifications similar to post-translational modifications in living organisms under plasma treatment, which play a key role in protein function. We present a modeling study on the interactions of plasma and peptides by a Reactive Molecular Dynamic (RMD) simulation. The formation and breaking of chemical bonds and the generation of new reactive groups on the structure of peptides are investigated upon impact of reactive oxygen species (ROS), and the final products are given, which agree well with the experimental observation. Further details can be found in the article by Yun Han Ding, Xiao Long Wang, Shu Qi Tian, Shan Rui Li, Lian Li, Quan Xin Li, Tong Zhao, and Yuan Tao Zhang (e2200148)

Role of Haptoglobin in Protecting the Toxic Effects of Hemoglobin in Various Pathologies

The review presents modern domestic and foreign literature data on the blood plasma protein haptoglobin, its structure, synthesis, function and interaction with hemoglobin. The ability of haptoglobin in interaction with hemoglobin to reduce the toxic effect of the latter is shown. Clinical studies of such interaction in various pathological conditions such as diabetes mellitus, sickle cell anemia, malaria, sepsis, etc. are described. It is noted that the development of new haptoglobin derivatives can contribute to the prevention of hemoglobin toxicity in hemolytic diseases.

Real time reconstruction of the fast electron spectrum from high intensity laser plasma interaction using gamma counting technique

X-ray and gamma fluxes from the high intensity laser-plasma interaction are extremely short, well beyond temporal resolution of any detectors. If laser pulses come repetitively, the single photon counting technique allows to accumulate the photon spectra, however, its relation to the spectrum of the initial fast electron population in plasma is not straightforward. We present efficient and fast approach based on the Geant4 package that significantly reduces computer time needed to re-construct the high energy tail of electron spectrum from experimental data accounting for the pileup effect. Here, we first tabulate gamma spectrum from monoenergetic electron bunches of different energy for a given experimental setup, and then compose the simulated spectrum. To account for the pileups, we derive analytical formula to reverse the data. We also consider errors coming from the approximation of the initial electron spectrum by the sum of monoenergetic impacts, the finite range of the electron spectrum, etc. and give estimates on how to choose modelling parameters to minimize the approximation errors. Finally, we present an example of the experimental data treatment for the case of laser-solid interaction using 50 fs laser pulse with intensity above 1018 W/cm2.

Low-Temperature H2/D2 Plasma–W Material Interaction and W Dust Production for Fusion-Related Studies

In this paper, results concerning hydrogen and deuterium plasma (RF, 13.56 MHz) interactions with tungsten surfaces, were reported. We used the Hollow-Cathode (HC) configuration for plasma–tungsten surface interaction experiments, along with the collection of tungsten dust, at different distances. Further on, the plasma-exposed tungsten surfaces and the collected dust were morphologically analyzed by contact profilometry, scanning electron microscopy, and energy dispersive spectroscopy measurements, along with chemical investigations by the X-ray photoelectron spectroscopy technique. The results showed that exposing the tungsten surfaces to the hydrogen plasma induces surface erosion phenomena along with the formation of dust and interconnected W structures. Herein, the mean ejected material volume was ~1.1 × 105 µm3. Deuterium plasma facilitated the formation of blisters at the surface level. For this case, the mean ejected material volume was ~3.3 × 104 µm3. For both plasma types, tungsten dust within nano- and micrometer sizes could be collected. The current study offers a perspective of lab-scaled plasma systems, which are capable of producing tungsten fusion-like surfaces and dust.

Production of a large volume non-equilibrium region in an atmospheric argon arc plasma with a counter injection of cold gas from an annular anode

In this letter, an annular anode is designed for producing arc plasmas with a large non-equilibrium region by using a counterflow cold gas through the annular anode. The coupled mass-momentum-energy exchange processes in an argon arc plasma are studied numerically and experimentally. The counter-injection of the cold argon gas from the center of the anode leads to a steep gradient of the heavy-particle temperature due to the formation of a thin stagnation layer resulting from the interaction of the high temperature plasma with the cold gas; and in particular, a large volume non-equilibrium ‘dark’ plasma region is obtained above the anode surface. The results show that, with the enhancement of the convective heat transfer process in the plasma core region, the fraction of the non-equilibrium region to the whole arc plasma region reaches 92.2% where the heavy-particle temperature can be reduced significantly, e.g. ∼2300 K, while simultaneously, the electron temperature and number density are remained at high levels greater than 8000 K and 2.4 × 1020 m−3, respectively, under the operating condition studied in this letter. This research not only deepens the understanding to the non-equilibrium synergistic transport mechanisms of arc plasmas, but also provides a method for producing a large volume non-equilibrium plasma region so as to promote various existing applications, or even creating new applications in the future.

The effect of longitudinal static magnetic field on the radiation efficiency of high harmonics from overdense plasma

The effect of the magnetic field applied along the laser propagation direction on the radiation efficiency of high-order harmonics generated from laser-irradiated overdense plasma is investigated theoretically and numerically. We find that the external magnetic field can increase the transmittance of the overdense target, thereby dramatically enhancing the energy coupling between the laser and target. While for high-order harmonics of the laser reflected from the oscillating target, the radiation efficiency reaches the maximum when the cyclotron frequency of the electrons in the magnetized target approaches the laser frequency. This conclusion applies only to overdense plasmas targets. For targets with low reflectivity, the application of the magnetic field reduces the harmonic radiation efficiency due to the decrease of both the oscillating coherence and opacity of the target. This work provides a reasonable approach to improving the radiation efficiency of high-order harmonics and a method to estimate the magnitude of the self-generated magnetic field during intense laser–plasma interactions.

Physics-separating artificial neural networks for predicting initial stages of Al sputtering and thin film deposition in Ar plasma discharges

Simulations of Al thin film sputter depositions rely on accurate plasma and surface interaction models. Establishing the latter commonly requires a higher level of abstraction and means to dismiss the fundamental atomic fidelity. Previous works on sputtering processes addressed this issue by establishing machine learning surrogate models, which include a basic surface state (i.e. stoichiometry) as static input. In this work, an evolving surface state and defect structure are introduced to jointly describe sputtering and growth with physics-separating artificial neural networks. The data describing the plasma–surface interactions (PSIs) stem from hybrid reactive molecular dynamics/time-stamped force bias Monte Carlo simulations of Al neutrals and Ar+ ions impinging onto Al(001) surfaces. It is demonstrated that the fundamental processes are comprehensively described by taking the surface state as well as defect structure into account. Hence, a machine learning PSI surrogate model is established that resolves the inherent kinetics with high physical fidelity. The resulting model is not restricted to input from modeling and simulation, but may similarly be applied to experimental input data.

Cumulative ejection of terahertz radiation from a laser-driven magnetized plasma

We propose a scheme for efficient directional emission of laser-driven wakefields from a magnetized plasma. In the scheme, a laser–plasma interaction region is sandwiched between a pair of dielectric prisms of total internal reflection. The wakefields, propagating in the plasma at different angles to the laser beam, are cumulated by the prisms and radiated to free space in the direction of the laser beam. For magnetic fields <100 T, a 50-fs laser pulse with 1-J energy can generate long lasting (hundreds of ps) multicycle terahertz radiation with mJ-level energy. For a 500-T field, the laser pulse can generate terahertz bursts with a uniform spectrum in the ∼7–14 THz interval with ten-mJ-level energy.

Genetic Risk for Alzheimer Disease and Plasma Tau Are Associated With Accelerated Parietal Cortex Thickness Change in Middle-Aged Adults.

Neuroimaging and biomarker studies in Alzheimer disease (AD) have shown well-characterized patterns of cortical thinning and altered biomarker concentrations of tau and β-amyloid (Aβ). However, earlier identification of AD has great potential to advance clinical care and determine candidates for drug trials. The extent to which AD risk markers relate to cortical thinning patterns in midlife is unknown. The first objective of this study was to examine cortical thickness change associated with genetic risk for AD among middle-aged military veterans. The second objective was to determine the relationship between plasma tau and Aβ and change in brain cortical thickness among veterans stratified by genetic risk for AD. Participants consisted of post-9/11 veterans (N = 155) who were consecutively enrolled in the Translational Research Center for TBI and Stress Disorders prospective longitudinal cohort and were assessed for mild traumatic brain injury (TBI) and posttraumatic disorder (PTSD). Genome-wide polygenic risk scores (PRSs) for AD were calculated using summary results from the International Genomics of Alzheimer's Disease Project. T-tau and Aβ40 and Aβ42 plasma assays were run using Simoa technology. Whole-brain MRI cortical thickness change estimates were obtained using the longitudinal stream of FreeSurfer. Follow-up moderation analyses examined the AD PRS × plasma interaction on change in cortical thickness in AD-vulnerable regions. Higher AD PRS, signifying greater genetic risk for AD, was associated with accelerated cortical thickness change in a right hemisphere inferior parietal cortex cluster that included the supramarginal gyrus, angular gyrus, and intraparietal sulcus. Higher tau, but not Aβ42/40 ratio, was associated with greater cortical thickness change among those with higher AD PRS. Mild TBI and PTSD were not associated with cortical thickness change. Plasma tau, particularly when combined with genetic stratification for AD risk, can be a useful indicator of brain change in midlife. Accelerated inferior parietal cortex changes in midlife may be an important factor to consider as a marker of AD-related brain alterations.

Sunspots and their cycle

These dark blemishes on stars are key to understanding the interaction of strong magnetic fields and dynamic plasma.