Warm Plasma Research Articles

Particle‐in‐Cell Simulations of the Fast Magnetosonic Mode in a Dipole Magnetic Field: 1‐D Along the Radial Direction

AbstractAn electromagnetic particle‐in‐cell code is used to investigate self‐consistent evolution of the fast magnetosonic mode in a one‐dimensional configuration along the radial direction in a dipole background magnetic field. A previous observation of this wave mode is used to select the simulation parameters. A partial shell velocity distribution of energetic protons with a moderate pitch angle anisotropy is used to excite the waves self‐consistently. Consistent with local linear theory analysis, wave growth occurs only at exact harmonics of the local proton cyclotron frequency, Ωp. However, radial propagation quickly removes the waves from the region where they can grow, leading to a time scale of wave amplification much longer than that predicted by linear theory. In addition, radial propagation from multiple wave sources makes the frequency spectrum measured at a single point much broader. The warm background plasma plays an important role in two ways. First, it increases the phase speed of the fast magnetosonic mode; and second, it causes the breakup of the extraordinary mode dispersion relation in the vicinity of the harmonics, where the broken dispersion curves are connected with multiple ion Bernstein modes. In this case, the waves propagating radially are absorbed at locations where their frequency reaches integer multiples of Ωp and background protons experience perpendicular heating at those locations.

Investigation of Ion-Acoustic Solitons in Magnetosphere and Tokamak Warm Plasma with Two-Temperature Electrons

The properties of oblique propagation of small amplitude ion-acoustic soliton are investigated in a plasma containing weakly relativistic ions and two-temperature electrons (cold and hot electrons). The reductive perturbation method is used to derive the Korteweg−de Vries equation for the present plasma model. It is found that the parameters determining the nature of soliton are different for compressive or rarefactive structures. Moreover, the effects of weakly relativistic ions, the temperature ratio, and the density ratio of hot-to-cold electron species on soliton characters are studied. The theory is applied on the case of relativistic ions observed in the magnetosphere and in the case of nonrelativistic ions observed in tokamaks.

Dispersion characteristics and excitation of space-charge and cyclotron modes in inhomogeneous warm plasma waveguide

In this paper, we are going to investigate the effects of plasma parameters on dispersion characteristics of electrostatic modes in a cylindrical inhomogeneous warm magnetized plasma waveguide. To this aim, the radial inhomogeneity for different characteristic length with strongly spatial dispersion are taken into account. Due to radial inhomogeneity of plasma, all essential equations for studying the properties of dispersion are calculated in Bessel–Fourier and differential Bessel–Fourier expansion. Moreover, two cases of strong and weak magnetic fields are considered for the analyses. We show that there was just an interval in which the space-charge and cyclotron modes are excited. We called it the Longitudinal Wavenumber Excitation Interval that is due to the thermal effect consideration. The effect of different radial inhomogeneity characteristic length on the dispersion properties is also studied in this work.

Warm Plasma Torch for Hydrocarbon Reforming

This paper treats over a reforming process using a warm plasma reactor for CH4 and CO2 conversion and hydrogen yield recovering. The conversion of hydrocarbon in syngas is mainly contributed by dissociation and ionization processes. Warm plasma is environment-friendly and autosustainable process; in addition, the electric discharge has low specific energy (SE) requirement and is able to retain enough high temperature to produce excited species and support subsequent chemical reactions. Such plasma discharges have significant advantages: do not require extra cooling systems, since they work with reduced electric current and high voltages, decreasing significantly electrode erosion. Consequently, reactors can be accomplished with a simpler framework and high gas treatment capacity. Plasma interaction with greenhouse gases (GHGs) leads into a molecular dissociation, mainly forming CO and H2, also known as syngas. In recent years, the syngas has become one of the alternative energy sources, which is more profitable and investigated. This mixture, normally recovered from organic material decomposition, provides energy with innovative applications in microturbines and fuel cells, in conjunction with other applications. In addition, an experimental analysis by using pulsed or resonant converter power supply is conducted; this converter enables the maximum energy transfer into plasma discharge without requiring complex electronic structures. Electric analysis was performed to determine instantaneous current, voltage, and power applied in the warm plasma torch for GHG treatment. From the analysis of power consumption, flux flow rate, and other physical chemical characteristics, SE and energy conversion efficiency are obtained. The effect of frequency in voltage–current relationship, depending on the waveform source, is described here. The input and exhaust gases were analyzed by a mass spectrometer and a gas analyzer. A comparison of these results with other results obtained in different bibliographic references is also signaled.

Carbon Nanostructures Deposition on Surfaces Treated by Warm Plasma Processes

To improve the adhesion of carbon nanostructures (CNSs) in different surfaces, atmospheric nitrogen discharges, obtained with a warm plasma torch, were used. The deposition of substances containing CNSs (synthesized by arc discharge) on these surfaces was realized by an electrospinning technique. The morphology was analyzed by scanning electron microscope in order to confirm the deposition of CNSs on the treated and untreated surfaces. An elemental analysis was performed by energy-dispersive X-ray spectroscopy. The analysis of the surface quality was done by the contact angle technique.

A perturbation theory for equation of state of hydrogen in warm and hot dense regimes

In the warm dense regime of hydrogen plasma where the ions and the electrons are strongly coupled, few theoretical models for equation of state (EOS) exist which are accurate enough and simple to implement. In the recent past, we have developed a method for calculating the Helmholtz free energy of a mixture of ions and electrons by combining the orbital-free quantum hypernetted chain (QHNC) method with perturbation theory treating the electron-ion interaction as a perturbation over a reference system of one component plasma (OCP) and uniform electron gas (UEG). However, it was assumed that electrons were at zero Kelvin and a crude formula for the free energy of the UEG was used. This limited the applicability of the method to a small density-temperature regime. In the present work, a finite temperature extension to the orbital-free QHNC theory is derived and is employed in the perturbation theory we developed. Also, an accurate formula given by Ichimaru is used for the free energy of the UEG. EOS, ionic, and electronic structures of fully ionized hydrogen plasma are obtained using the improved method for a wide range of densities and temperatures in the warm and hot dense plasma regimes. The results of the present method are in excellent agreement with those of simulation data for pressures above 1Mbar. It is observed that, above 5 eV, the reference system, i.e., the OCP + UEG, gives the most dominant contribution to EOS and the contribution of perturbation terms is limited to 5%.

Measurement of temperature and density using non-collective X-ray Thomson scattering in pulsed power produced warm dense plasmas

We present the first experimental measurement of temperature and density of a warm dense plasma produced by a pulsed power driver at the Nevada Terawatt Facility (NTF). In the early phases of discharge, most of the mass remains in the core, and it has been challenging to diagnose with traditional methods, e.g. optical probing, because of the high density and low temperature. Accurate knowledge of the transport coefficients as well as the thermodynamic state of the plasma is important to precisely test or develop theoretical models. Here, we have used spectrally resolved non-collective X-ray Thomson scattering to characterize the dense core region. We used a graphite load driven by the Zebra current generator (0.6 MA in 200 ns rise time) and the Ti He-α line produced by irradiating a Ti target with the Leopard laser (30 J, 0.8 ns) as an X-ray probing source. Using this configuration, we obtained a signal-to-noise ratio ~2.5 for the scattered signal. By fitting the experimental data with predicted spectra, we measured T = 2±1.9 eV, ρ = 0.6±0.5 gr/cc, 70 ns into the current pulse. The complexity of the dense core is revealed by the electrons in the dense core that are found to be degenerate and weakly coupled, while the ions remain highly coupled.

Warm-plasma catalytic reduction of CO2 with CH4

Toward developing an efficient plasma-based technique for CO2 reduction with CH4, warm-plasma catalytic (WPC) reduction of CO2 with CH4 in a reactor using gliding arc discharge and Ni/CeO2/Al2O3 catalyst is reported. In the warm plasma (WP) case, besides dry reforming reaction, reverse water gas shift (RWGS) reaction also comparably contributes for CO2 reduction. Although the contribution of dry reforming reaction is significantly enhanced by the increase of CH4/CO2 ratio, it accounts for only 60% due to the limitation of maximum CH4/CO2 ratio by the serious carbon deposition at CH4/CO2 >1/2. In addition, the low CH4/CO2 ratio also results in the low CO2 conversion, H2/CO ratio and H2 selectivity. In the WPC case, extra CH4 was fed after plasma to increase the CH4/CO2 ratio to 1, dry reforming reaction becomes the major contributor of CO2 reduction. Under the conditions of specific energy input of 86 kJ/mol, total flow rate of 2.67 SLM, catalyst-bed temperature of 850 °C and gas hourly space velocity of 3200 h−1, CO2 conversion of 91% and CH4 conversion of 94% with H2/CO = 1 and nearly 100% H2 selectivity are achieved with a CO2 energy cost of 598 kJ/mol and an energy efficiency of 72%.

Validation of OSHUN against collisionless and collisional plasma physics

OSHUN, a Vlasov–Fokker–Planck–Maxwell code, is successfully validated against a few collisionless and collisional plasma physics test problems. In OSHUN, the distribution function is expanded in velocity (or momentum) space into an arbitrary number of spherical harmonics. OSHUN is shown to accurately recover Landau damping by including a relatively small number of spherical harmonics for an initial value problem as well as a driven plasma wave. The Fokker–Planck operator (both electron–electron and electron-ion) is shown to be able to reproduce the Epperlein–Haines heat-flow coefficient in warm, un-magnetized and magnetized plasmas with varying degrees of ionization. These collisionless and collisional problems are of disparate time- and length- scales ranging from femtoseconds to nanoseconds, and from microns to millimeters. OSHUN's ability to handle these test problems successfully illustrates the power of the spherical-harmonic expansion when studying both weakly-collisional and collisional plasmas relevant to high-energy-density physics. The implementation and use of new features such as a ponderomotive wave driver and an implicit collision operator is also discussed.

Analysis of Landau damping in radially inhomogeneous plasma column

The Landau damping behavior in a cylindrical inhomogeneous warm magnetized plasma waveguide has been studied. The radial inhomogeneity for different characteristic lengths (L0) with strong spatial dispersion has been taken into account. The analyses have been considered for two limits and . Due to the radial inhomogeneity of the plasma, all essential equations for studying the Landau damping are calculated in the Bessel–Furrier and differential Bessel–Furrier expansions. The dependence of Landau damping on the inhomogeneity, temperature and external magnetic field for electrostatic modes is scrutinized and described in detail through numerical calculations. The associated numerical results are presented and discussed.

Plasma activation of methane for hydrogen production in a N2 rotating gliding arc warm plasma: A chemical kinetics study

In this work, a chemical kinetics study on methane activation for hydrogen production in a warm plasma, i.e., N2 rotating gliding arc (RGA), was performed for the first time to get new insights into the underlying reaction mechanisms and pathways. A zero-dimensional chemical kinetics model was developed, which showed a good agreement with the experimental results in terms of the conversion of CH4 and product selectivities, allowing us to get a better understanding of the relative significance of various important species and their related reactions to the formation and loss of CH4, H2, and C2H2 etc. An overall reaction scheme was obtained to provide a realistic picture of the plasma chemistry. The results reveal that the electrons and excited nitrogen species (mainly N2(A)) play a dominant role in the initial dissociation of CH4. However, the H atom induced reaction CH4 + H → CH3 + H2, which has an enhanced reaction rate due to the high gas temperature (over 1200 K), is the major contributor to both the conversion of CH4 and H2 production, with its relative contributions of >90% and >85%, respectively, when only considering the forward reactions. The coexistence and interaction of thermochemical and plasma chemical processes in the rotating gliding arc warm plasma significantly enhance the process performance. The formation of C2 hydrocarbons follows a nearly one-way path of C2H6 → C2H4 → C2H2, explaining why the selectivities of C2 products decreased in the order of C2H2 > C2H4 > C2H6.

Resolving the Inner Arcsecond of the RY Tau Jet with HST

Abstract Faint X-ray emission from hot plasma (T x > 106 K) has been detected extending outward a few arcseconds along the optically delineated jets of some classical T Tauri stars including RY Tau. The mechanism and location where the jets are heated to X-ray temperatures are unknown. We present high spatial resolution Hubble Space Telescope (HST) far-ultraviolet long-slit observations of RY Tau with the slit aligned along the jet. The primary objective was to search for C iv emission from warm plasma at T C iv ∼ 105 K within the inner jet (<1″) that cannot be fully resolved by X-ray telescopes. Spatially resolved C iv emission is detected in the blueshifted jet extending outward from the star to 1″ and in the redshifted jet out to 0.″5. C iv line centroid shifts give a radial velocity in the blueshifted jet of −136 ± 10 km s−1 at an offset of 0.″29 (39 au) and deceleration outward is detected. The deprojected jet speed is subject to uncertainties in the jet inclination, but values ≳200 km s−1 are likely. The mass-loss rate in the blueshifted jet is at least M ˙ jet , blue = 2.3 × 10 − 9 M ⊙ yr−1, consistent with optical determinations. We use the HST data along with optically determined jet morphology to place meaningful constraints on candidate jet-heating models including a hot-launch model in which the jet is heated near the base to X-ray temperatures by an unspecified (but probably magnetic) process, and downstream heating from shocks or a putative jet magnetic field.

Fluorescence and absorption spectroscopy for warm dense matter studies and ICF plasma diagnostics

The burning core of an inertial confinement fusion (ICF) plasma produces bright x-rays at stagnation that can directly diagnose core conditions essential for comparison to simulations and understanding fusion yields. These x-rays also backlight the surrounding shell of warm, dense matter, whose properties are critical to understanding the efficacy of the inertial confinement and global morphology. We show that the absorption and fluorescence spectra of mid-Z impurities or dopants in the warm dense shell can reveal the optical depth, temperature, and density of the shell and help constrain models of warm, dense matter. This is illustrated by the example of a high-resolution spectrum collected from an ICF plasma with a beryllium shell containing native iron impurities. Analysis of the iron K-edge provides model-independent diagnostics of the shell density (2.3 × 1024 e/cm3) and temperature (10 eV), while a 12-eV red shift in Kβ and 5-eV blue shift in the K-edge discriminate among models of warm dense matter: Both shifts are well described by a self-consistent field model based on density functional theory but are not fully consistent with isolated-atom models using ad-hoc density effects.

Detection of low-metallicity warm plasma in a galaxy overdensity environment at z ∼ 0.2

We present results from the analysis of a multiphase O vi–broad Ly α (BLA) absorber at z = 0.19236 in the HubbleSpaceTelescope/Cosmic Origins Spectrograph spectrum of PG 1121 + 422. The low and intermediate ionization metal lines in this absorber have a single narrow component, whereas the Ly α has a possible broad component with |$b({{\rm H}\,\small {I}}) \sim 71$| km s−1. Ionization models favour the low and intermediate ions coming from a T ∼ 8500 K, moderately dense (n H ∼ 10 − 3 cm−3) photoionized gas with near solar metallicities. The weak O vi requires a separate gas phase that is collisionally ionized. The O vi coupled with BLA suggests T ∼ 3.2 × 105 K, with significantly lower metal abundance and ∼1.8 orders of magnitude higher total hydrogen column density compared to the photoionized phase. Sloan Digitial Sky Survey (SDSS) shows 12 luminous (>L*) galaxies in the ρ ≤ 5 Mpc, |Δv| ≤ 800 km s−1 region surrounding the absorber, with the absorber outside the virial bounds of the nearest galaxy. The warm phase of this absorber is consistent with being transition temperature plasma either at the interface regions between the hot intragroup gas and cooler photoionized clouds within the group, or associated with high velocity gas in the halo of a ≲L* galaxy. The absorber highlights the advantage of O vi–BLA absorbers as ionization model independent probes of warm baryon reserves.

On-Board Hydrogen Production: Warm Plasma Chain Catalysis

Here we demonstrate an advanced on-board hydrogen production by warm plasma chain catalysis for fuel-cell electric vehicles (FCEVs) with high specific productivity and transient operation. Methanol, air and steam reactants as two specific feeds are fed into the reactor without soot formation and catalyst sintering. Oxidative pyrolysis reaction (OPR) by plasma, steam reforming (SR), and pyrolysis at high temperature, and SR and water gas shift (WGS) at medium temperature over catalysts occur subsequently for the coupled process. The heat with OPR is efficiently utilized by the subsequent endothermic reactions. Hydrogen selectivity of 99% (59 vol.%, 4.1 SLM) with methanol conversion of 92% is achieved. A fascinating match of energy efficiency of 91% (of methanol to hydrogen) and the atomic hydrogen generation of 88% is stressed. It can be attributed to the chain catalysis of (oxidative) pyrolysis and WGS in sequence (as well as SR), which is initiated by warm plasma.

The Influence of the Motion of a Strongly Magnetized Plasma on Radiation from a Traveling-Wave Antenna

We consider the problem of radiation from a traveling-wave antenna in a warm electron plasma which moves along a strong magnetic field at a constant velocity. To describe the electromagnetic properties of the plasma, we use the diagonal tensor of dielectric permittivity, which is calculated for a magnetized plasma with the Maxwellian electron velocity distribution allowing for collisions of electrons with neutral molecules. The dispersion relation is analyzed numerically, and expressions for the field amplitudes in the wave zone are obtained. The radiation resistance of the antenna is calculated. It is shown that as the phase velocity of the traveling current wave in the antenna approaches the average velocity of the plasma motion, the radiation field decreases exponentially with distance from the source as a result of the efficient transfer of the wave energy to the plasma electrons due to collisionless interaction.

Negative Potential Solitary Structures in the Magnetosheath With Large Parallel Width

AbstractWe report multispacecraft observations by the Magnetospheric MultiScale (MMS) mission of large (80–155 λDe parallel to B) electrostatic solitary waves (ESWs). Observations of the same ESWs at different positions and times enable unprecedented accuracy in determining the size, velocity, and evolution of these nonlinear structures. This particular event is a short series of negative potential solitary waves in the magnetosheath. The observed structures differ in amplitude and speed, merging or colliding with one another. A Vlasov simulation supports initial wave growth by a cold feature in the electron distribution function. Such cold electrons are likely the result of mixing between the cold magnetospheric and warm magnetosheath plasma along a reconnection separatrix. ESW speed and perpendicular size are inconsistent with ion phase space holes. Solving Poisson's equation for the measured potential, we find a reduction in electron density rather than an enhancement expected from an electron soliton. These ESWs have an unusual combination of properties on both ion and electron scales, likely supported by a complex electron distribution in the nonlinear state.

Investigation of solitary waves in multi component warm plasma with weakly relativistic effect in all the species

Investigation of solitary waves in multi component warm plasma with weakly relativistic effect in all the species

Updating Conductivity Tensor of Cold and Warm Plasma for Equatorial Ionosphere F2-Region in The Northern Hemisphere

We compared the conductivity tensor becoming important parameter of ionospheric plasma using the real geometry of Earth’s magnetic field in the Northern hemisphere for both cold and warm ionospheric plasma for equinox days. It could be that the conductivity tensor certainly depends on the vector of wave propagation (k) and the adiabatic sound speed (Ue) in warm ionospheric plasma and it is possible to say that the adiabatic sound speed for electron generally decreases the magnitudes of conductivity tensor components with respect to the cold ionosphere plasma except for $$\sigma_{{ 2 3 {\text{R}}}}^{\prime }$$ (Ue ≠ 0) = $$\sigma_{{ 2 3 {\text{R}}}}$$ (Ue = 0), $$\sigma_{{ 3 3 {\text{R}}}}^{\prime }$$ (Ue ≠ 0) = $$\sigma_{{ 3 3 {\text{R}}}}$$ (Ue = 0), $$\sigma_{{ 1 3 {\text{S}}}}^{\prime }$$ (Ue ≠ 0) = $$\sigma_{{ 1 3 {\text{S}}}}$$ (Ue = 0) and $$\sigma_{{ 3 3 {\text{S}}}}^{\prime }$$ (Ue ≠ 0) = $$\sigma_{{ 3 3 {\text{S}}}}$$ (Ue = 0). In this sense, the resistivity and reactance increase in ionospheric plasma. In this context, according to the accepted conditions, the change of conductivity with local time is similar to change of electron density with local time for both (cold and warm) conditions in ionospheric plasma as trend.

Propagational characteristics in a warm hybrid plasmonic waveguide

We theoretically analyze the properties of guided modes in a warm planar conductor–gap–dielectric (CGD) system. The latter consists of a high index dielectric, separated from a warm metallic plasma with a low index nano-sized dielectric layer (gap) by using the hydrodynamic model coupled to Maxwell's equations. The effects of thermal pressure on the confinement and the propagation losses of Hybrid Plasmon Polariton (HPP) modes are studied. We found that the thermal effect leads to a reduction in the effective refractive index as well as in the propagation losses of the HPP mode. Furthermore, the cutoff thickness in the warm CGD waveguide is found to be smaller than that in a cold CGD waveguide. The results may be useful in understanding the essential physics of active/passive Plasmonic devices and chip-scale systems.