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Density filamentation has been observed in many beam-plasma simulations and experiments. Because current filamentation is a pure transverse mode, charge density filamentation cannot be produced directly by the current filamentation process. To explain this phenomenon, several mechanisms are proposed such as the coupling of the Weibel instability to the two-stream instability, coupling to the Langmuir wave, differences in thermal velocities between the beam and return currents, the magnetic pressure gradient force, etc. In this paper, it is shown that the gradient of the Lorentz factor can, in fact, represent the nonlinear behavior of a plasma fluid and further that the nonuniform Lorentz factor distribution can give rise to electrostatic fields and density filaments. Simulation results together with theoretical analyses are presented.

We study dynamical screening effects of nuclear charge on big bang nucleosynthesis (BBN). A moving ion in plasma creates a distorted electric potential leading to a screening effect which is different from the standard static Salpeter formula. We consider the electric potential for a moving test charge, taking into account dielectric permittivity in the unmagnetized Maxwellian plasma during the BBN epoch. Based on the permittivity in a BBN plasma condition, we present the Coulomb potential for a moving nucleus, and show that enhancement factor for the screening of the potential increases the thermonuclear reaction rates by a factor order of 10^(-7). In the Gamow energy region for nuclear collisions, we find that the contribution of the dynamical screening is less than that of the static screening case, consequently which primordial abundances hardly change. Based on the effects of dynamical screening under various possible astrophysical conditions, we discuss related plasma properties required for possible changes of the thermal nuclear reactions.

The transport dynamo mechanism, which describes the magnetic field generation by diffusion flow is reviewed. In this mechanism, the cross-field transport caused by the random motion of fluid breaks the frozen-flux approximation, and the resulting cross-field diffusion that can generate the magnetic field. Turbulence can play an important role in inducing such random motion. Compared to the conventional dynamo mechanism, this transport mechanism has several special features that the field generation can occur on a very slow time scale because the mechanism is mediated by diffusion and that this mechanism is practically meaningful only when there is density inhomogeneity. Turbulence can significantly enhance cross-field diffusion far beyond collisional transport. The physical meanings of the diffusion-generated magnetic fields are discussed in detail., Comment: 13 pages,2 figures

A direct acceleration scheme to generate high-energy, high-charge electron beams with an intense few-cycle Laguerre–Gaussian (LG) laser pulse was investigated using three-dimensional particle-in-cell simulations. In this scheme, an intense LG laser pulse was irradiated onto a solid density plasma slab. When the laser pulse is reflected, electrons on the target front surface are injected into the longitudinal electric field of the laser and accelerated further. We found that the carrier-envelope phase (CEP) of the few-cycle laser pulse plays a key role in the electron injection and acceleration process. Using a three-cycle LG laser pulse with a 0 = 2 and an appropriate CEP, an about 60 pC electron beam could be obtained at a maximum energy of 16 MeV. In comparison, when a laser pulse with mismatched CEP was used, a total of 4 pC electron beam with a maximum energy of 3.5 MeV was obtained. Linear scaling of electron energy to the laser strength was shown up to a 0 = 100 at which a quasi-monoenergetic electron beam of 850 MeV energy with a charge equal to 600 pC could be obtained. These results demonstrate that high-energy electron beams can be stably generated through direct laser acceleration using a CEP-controlled intense few-cycle LG laser pulse.

With the recent advances in ultrahigh intensity lasers, exotic astrophysical phenomena can be investigated in laboratory environments. Collisionless shock in a plasma, prevalent in astrophysical events, is produced when a strong electric or electromagnetic force induces a shock structure in a time scale shorter than the collision time of charged particles. A near-critical-density (NCD) plasma, generated with an intense femtosecond laser, can be utilized to excite a collisionless shock due to its efficient and rapid energy absorption. We present electrostatic shock acceleration (ESA) in experiments performed with a high-density helium gas jet, containing a small fraction of hydrogen, irradiated with a 30 fs, petawatt laser. The onset of ESA exhibited a strong dependence on plasma density, consistent with the result of particle-in-cell simulations on relativistic plasma dynamics. The mass-dependent ESA in the NCD plasma, confirmed by the preferential reflection of only protons with two times the shock velocity, opens a new possibility of selective acceleration of ions by electrostatic shock.

The implication of the Biermann battery (BB) on turbulent magnetic field amplification in colliding plasma jets produced by high-power lasers is studied by using the FLASH code. It is found that the BB can play a significant role in turbulent field amplification. The small scale fluid structures introduced by turbulence can allow the BB to effectively amplify the magnetic field. When the flow is perpendicular to the magnetic field, the magnetic field amplification is shown to be greater than the case where the flow is parallel.

We propose a new ion acceleration scheme of irradiating a thin solid target with an ultraintense circularly polarized Laguerre–Gaussian (LG) laser pulse. Three-dimensional particle-in-cell simulations are performed to demonstrate that this scheme can generate a low-divergence high-density relativistic proton jet. By this scheme, the number of protons emitted with a small angle (

In many studies on the laser impinging on a plasma surface, an assumption is made that the reflection of a laser pulse propagating to a plasma surface takes place only at the turning point, at which the plasma density exceeds the critical one. A general reflection amplitude of light R from an arbitrary inhomogeneous medium can be obtained by solving a Riccati-type integral equation, which can be solved analytically in low-reflection conditions, i.e., |R|2 ≪ 1. In this work, we derive an intuitive analytic solution for the reflection amplitude of light R from a plasma surface by integrating all possible reflection paths given by the Fresnel equation. In the low-reflection condition, reflection paths having only one reflection event can be used. By considering the higher-order reflection paths, our analytic expression can describe reflection in the high-reflection condition. We show the results of a one-dimensional particle-in-cell simulation to support our discussions. Since our model derived for static plasmas is well corroborated by the simulation results, it can be a useful tool for analyzing light reflection from dynamically varying plasmas.

The recent advancement of high-intensity lasers has made all-optical Compton scattering become a promising way to produce ultra-short brilliant $\gamma$-rays in an ultra-compact system. However, so far achieved Compton $\gamma$-ray sources are severely limited by low conversion efficiency (lower than $10^{-5}$) and spectral intensity ($\sim10^{4}$ ${\rm photons/0.1\%BW}$). Here we present a highly efficient gamma photon emitter obtained by irradiating a high-intensity laser pulse on a miniature plasma device consisting of a plasma lens and a plasma mirror. This concept exploits strong spatiotemporal laser-shaping process and high-charge electron acceleration process in the plasma lens, as well as an efficient nonlinear Compton scattering process enabled by the plasma mirror. Our particle-in-cell simulations demonstrate that in this novel scheme, brilliant $\gamma$-rays with very high conversion efficiency (higher than $10^{-2}$) and spectral intensity ($\sim10^{9}$ ${\rm photons/0.1\%BW}$) can be achieved by employing currently available petawatt-class lasers with intensity of $10^{21}$ ${\rm W/cm^2}$. Such efficient and intense $\gamma$-ray sources would find applications in wide-ranging areas., Comment: 19 pages, 8 figures

A self-guided Gaussian laser pulse propagating in a non-uniform plasma channel is unstable to a plasma wave perturbation co-moving with the laser with its group velocity. The plasma wave amplitude has a maximum radial profile along the laser propagation axis. As the plasma wave propagates through a non-uniform plasma channel, the plasma wave perturbation causes focusing in the part of the laser that propagates with the electron density trough and defocusing in the part moving with the crest. This yields an axial gradient in the intensity of the laser and produces a ponderomotive force on the electrons. The ponderomotive force drives the plasma wave, which in turn makes the modulational instability grow. The growth rate of the modulational instability becomes larger with the increase in non-uniformity of a shallow plasma channel. In a deep cavitated plasma channel the growth rate of the modulational instability increases with the laser pulse amplitude.

We study the generation of resonant third harmonic laser radiation in a density non-uniform rippled plasma channel. An introduction of plasma channel non-uniformity strongly enhances the self-focusing and compression of main laser pulse at lower powers. In a deeper plasma channel, self-focusing is less sensitive to laser amplitude variation but increases compression. Plasma density ripple ‘nq’ leading to resonant third harmonic generation when kq = 4ω2p/3meω0cγ0, where ‘ω’p is electron plasma frequency, ‘ω0’ is laser frequency, and ‘γ0’ is the electron Lorentz factor. Third harmonic is produced through the beating of ponderomotive force induced second harmonic density oscillations and the oscillatory velocity of electrons at main laser frequency. The self-focusing and compression of the fundamental pulse periodically enhances the intensity of the third-harmonic pulse at lower powers of main laser. In a deeper plasma channel, the third harmonic power is less effective by self-focusing and the compression of main laser, and increase with main laser pulse power.

Electromagnetic radiation at the plasma frequency and/or its second harmonic, the so-called plasma emission, is widely accepted as the fundamental process responsible for solar type II and III radio bursts. There have also been occasional observations of higher-harmonic plasma emissions in the solar-terrestrial environment. This paper presents the first demonstration of multiple harmonic emission by means of two-dimensional electromagnetic particle-in-cell simulation. This finding indicates that under certain circumstances the traditional mechanism of fundamental-harmonic pair emission might also be accompanied by higher-harmonic components. Consequently, the present findings are highly relevant to in situ observations of third- and/or higher-harmonic plasma emission in astrophysical and solar-terrestrial environments.

A two-dimensional electromagnetic particle-in-cell simulation of the beam-plasma interaction process is carried out to study the electromagnetic radiation at the plasma frequency and its second harmonic. In the simulation, a homogeneous plasma background with a periodic boundary condition is assumed. Electromagnetic radiation at the plasma frequency and its higher harmonics are widely believed to be responsible for solar type-II and type-III radio bursts. Traditional theory based upon weak turbulence of three-wave and nonlinear wave-particle interaction processes predicts radiation emission primarily at the fundamental and second harmonic of the plasma frequency. Electrostatic modes and electromagnetic radiation corresponding to this expectation at the fundamental and the second harmonics plasma frequencies are found. The radiation patterns of the fundamental and second harmonic electromagnetic modes are examined in detail.

to explain these nonlinear phenomena within the framework of the customary weak turbulence theory, so we put forth a theoretical explanation in the framework of the \generalized" weak turbulence theory. On the basis on the wave kinetic equation governing the interaction of a transverse electromagnetic (EM) wave with nonlinear harmonic Langmuir waves, it is found that an EM wave with a frequency in the vicinity of higher harmonics of the plasma frequency is amplied as a result of a nonlinear wave-wave interaction between the EM and the harmonic Langmuir waves. The dependency of the EM emission at higher harmonics on the angle dened with respect to the beam’s propagation direction is numerically examined by modeling the harmonic Langmuir wave spectrum.

Spatially resolved electron-energy-distribution functions (EEPFs) in a magnetized dual-frequency (60 and 2 MHz) capacitive discharge are numerically investigated by using one-dimensional particle-in-cell/Monte Carlo collision simulations. It is shown that the electron kinetic property of the EEPFs of the total energy in different spatial positions changes from being nonlocal to local by the magnetic field. Though the nonlocal property of the electrons between the discharge center and the vicinity of the high-frequency electrode disappears for a magnetic field of 100 G, the nonlocal property of the low-energy electrons is nearly conserved between the discharge center and the vicinity of the low-frequency electrode due to the secondary electrons emitted from the LF electrode. [1] S. J. You and H. Y. Chang, Phys. Plasmas 13, 043503 (2006)

An electromagnetic wave instantly converts an atomic cluster into a microsphere plasma, resulting in a displacement of the electron and the ion clouds. The electron and the Coulomb pressure cause an atomic cluster to explode and expand hydrodynamically. A nonlinear theory has been formulated to investigate the threshold intensity in cluster plasmas. A laser intensity exceeding 10 W/cm and a pulse duration of less than 1 picoseconds causes the onset of a stimulated Raman backscattered wave.

Dual-frequency capacitively coupled plasmas (DF-CCPs) have been used to control the ion flux by the high-frequency source and the ion bombardment energy onto the electrode by the low-frequency (LF) source separately. However, an increase in the LF voltage, which extends the maximum ion energy to a higher value, causes the reduction of the bulk plasma length with a subsequent decrease of the plasma density. By using a one-dimensional particle-in-cell/Monte Carlo simulation code, the effect of the magnetic field on a DF-CCP is investigated to find whether the plasma can be sustained during the LF voltage increase. It is found that a low magnetic field can effectively maintain the plasma density and electron temperature constant with respect to the variation of the LF voltage.

Electron distributions with various degrees of asymmetry associated with the energetic tail population are commonly detected in the solar wind near 1 AU. By numerically solving one-dimensional electrostatic weak turbulence equations the present paper demonstrates that a wide variety of asymmetric energetic tail distributions may result. It is found that a wide variety of asymmetric tail formation becomes possible if one posits that the solar wind electrons are initially composed of thermal core plus field-aligned counterstreaming beams, instead of the customary thermal population plus a single beam. It is shown that the resulting nonlinear wave-wave and wave-particle interactions lead to asymmetric nonthermal tails. It is found that the delicate difference in the average beam speeds associated with the forward versus backward components is responsible for the generation of asymmetry in the energetic tail.

The results of a particle-in-cell Monte Carlo collision (PIC-MCC) simulation of a direct current (DC) helium microplasma that operates at atmospheric pressure are presented. Electron and ion kinetic information that is not available from previous fluid studies is reported. Despite the high collisionality at atmospheric pressure, electrons are found to be in nonequilibrium. Similar to large-scale low-pressure dc discharges, the electron energy probability function (EEPF) in the bulk plasma presents three temperatures near the cathode, and it evolves into a bi-Maxwellian distribution as electrons approach the anode. The bi-Maxwellian character of the EEPF in the elastic energy region is not accounted for in fluid models, and as a result, PIC-MCC simulations predict a lower electron temperature than fluid models. The mean energy of ions that are impinging on the cathode is found to be significantly lower than in low-pressure discharges due to the large collisionality of the sheaths.

The influence of anisotropic ion pressure on the dust ion acoustic solitary wave (DIASW) and the double layer (DL) obliquely propagating to a magnetic field are investigated by using the Sagdeev potential. The anisotropic ion pressure is defined by applying the Chew–Goldberger–Low (CGL) theory, p ⊥ = p ⊥ 0 n and p ∥ = p ∥ 0 n 3 , where n is the normalized ion density. The solutions of DIASWs and DLs obliquely propagating to an external magnetic field are obtained in the small amplitude limit. It is found that the perpendicular component of anisotropic ion pressure works differently from that of the parallel component on the DIASWs in a magnetized dusty plasma, deviating from a straight extension of the isotropic pressure effect.

Ion saturation currents in a Hanbit mirror plasma have been analyzed by using the wavelet bispectral method. From this bicoherence analysis, an interesting phase coherent mode has been found at a very low frequency. This mode seems to be generated by the low frequency turbulence which could be identified as either ion drift waves or interchange modes. The wave coupling process leading to this coherent structure is found to follow the resonant three-wave coupling with an exact frequency match. A brief review is given on this coherent turbulence structure in a Hanbit mirror plasma.

The correlation dimension of edge turbulence associated with the density fluctuation in a mirror plasma has been analyzed. A low embedding dimension indicating a strange attractor in the phase space is found. A high correlation dimension is also found in the same plasma discharge, but it could not be determined for the embedding dimension below 15.

The nonlinear frequency shift of a low-frequency, coherent dust ion-acoustic wave in the presence of higher-frequency dust ion-acoustic turbulence is investigated in the framework of weak turbulence theory. It is found that the frequency shift of the dust ion-acoustic wave in an unmagnetized dusty plasma is always positive irrespective of the propagation direction of the coherent wave, as in the case of the customary ion-acoustic wave in the absence of dust particles. It is also found that the magnitude of the frequency shift decreases with increasing dust density.

The nonlinear frequency shift of a low-frequency, coherent dust-acoustic wave in the presence of higher frequency dust-acoustic turbulence is investigated in the framework of weak turbulence theory. It is found that the frequency shift of the dust-acoustic wave in an unmagnetized dusty plasma is always positive irrespective of the propagation direction of the coherent wave. It is also found that turbulent waves propagating in the same direction as the coherent wave are shown to give rise to a much higher frequency shift than the opposite case. Finally, it is shown that the nonlinear frequency shift of a dust-acoustic wave is more pronounced than in the case of the customary ion-acoustic waves in fully ionized plasmas.

In this article, particle kinetic equations which incorporate the nonlinear wave–particle interaction, as derived in P. H. Yoon [Phys. Plasmas 7, 4858 (2000)] and V. N. Tsytovich [Theory of Turbulent Plasma (Consultants Bureau, New York, 1977), pp. 103–110] are re-examined. A unified formalism is obtained after discrepancies in both references are resolved. The present particle kinetic equation is valid for the velocity space which does not satisfy the linear wave–particle resonance condition, ω−k⋅v≠0, but when the particle velocity of interest primarily satisfies the nonlinear wave–particle resonance, ω−ω′−(k−k′)⋅v=0.

Plasma treated polymer surface shows rapid hydrophobic recovery after plasma treatment. Surface rearrangement and the hydrophilicity change of low density polyethylene (LDPE) films with different degrees of crystallinity after oxygen plasma treatment were investigated using X-ray photoelectron spectroscopy (XPS) and water contact angle measurements. Since the mobility of polymer chain was restricted in the crystalline region, the chain movement of high crystalline polymer would be reduced. Water contact angles of quenched and annealed LDPE just after plasma treatment were almost same and oxygen contents of quenched LDPE was slightly higher than that of annealed LDPE. However, annealed LDPE showed slower contact angle raise and kept higher oxygen concentration than quenched LDPE with increasing aging time. By deconvolution of carbon XPS spectra, it was observed that major group contributed to decrease of oxygen contents was the hydroxyl groups and hydroxyl groups of quenched LDPE decayed faster than annealed LDPE while other oxygen species kept constant or decreased slightly. Increasing crystallinity reduce the surface rearrangement of polymer chain after plasma treatment.

X-ray photoelectron spectroscopy and near edge X-ray absorption fine structure investigation have been used to characterize the surfaces of two oxygen plasma-treated high-density polyethylene (HDPE) samples having different crystalline fractions. Both the observations indicate that a higher degree of crystallinity restricts the mobility of the polar functional groups on the HDPE surface. An increased crystalline order lowers the amount of oxidation and the aging of polar functional groups on the substrate surface. The results are supported by contact angle measurements and field emission scanning electron microscopic observations.

To improve the hydrophilicity and reduce the aging effect, argon and oxygen mixtures were employed in the plasma treatment of low-density polyethylene (LDPE). Argon resulted in producing more oxygen ions and radicals in the plasma than only oxygen and forming cross-linked layers on the LDPE surface. Therefore, the water contact angle on plasma-treated LDPE decreased and the oxygen content measured by X-ray photoelectron spectroscopy (XPS) increased with the increase of argon content. The aging effect was also much reduced with the increase of argon content since argon induced cross-linking.

The effects of cross-linking and crystallinity on the aging of plasma-treated high-density polyethylene (HDPE) have been investigated. In the case of mixed argon and oxygen, aging has been found to be reduced with an increased amount of argon in the mixture owing to an increased degree of cross-linking. A similar decrease in hydrophobic recovery has been achieved by increasing the crystallinity of HDPE. Diffusion of polar functional groups from the surface into the bulk has been observed to be lowered by both increasing the degree of cross-linking and crystallinity. The samples were analyzed by angle-resolved XPS, contact angle measurements and SEM investigations.

In a recent work, we have shown that the plasma flow around the magnetic island can excite the beta-induced Alfven eigenmode (BAE) (Marchenko et al 2016 Nucl. Fusion 56 106021). In the present communication, it is shown that coupling of this primary BAE and magnetic island generates secondary geodesic acoustic mode (GAM), which has the frequency and mode structure identical to those of the primary BAE. The fixed GAM/BAE amplitude ratio, determined by the plasma neutrality, is comparable with the plasma/magnetic pressure ratio. This nonlinear coupling can be responsible for axis-symmetric modes, which accompany island-driven Alfvenic modes observed on HL-2A tokamak (Chen et al 2013 Nucl. Fusion 53 113010).

A time-dependent many-body theory for many-particle systems is formulated using the functional Schr?dinger picture. Taking a Gaussian trial wave functional and using the variational principle, the equations of motion are obtained. The equations of motion are solved in the small oscillation regime to yield the generalized RPA results. The electron?hole excitation, the collective plasma oscillation for the paramagnetic state, the Stoner excitation and the spin wave for the ferromagnetic state are derived and discussed. As a further test on the versatility of the present method, the formalism is applied to the bound states of the exciton problem and shown to yield the governing equation in a straightforward manner.

The Kondo effect in a Luttinger liquid is studied using the renormalization group method. By renormalizing the boson fields, scaling equations to the second order for an arbitrary Luttinger interaction are obtained. For the ferromagnetic Kondo coupling, a spin bound state(triplet) can be realized without invoking a nearest neighbor spin interaction in agreement with the recent Bethe ansatz calculation. The scaling theory in the presence of the scalar potential shows that there is no interplay between the magnetic and non-magnetic interaction. Also a study on the crossover behavior of the Kondo temperature between the exponential and the power law type is presented., Comment: 9 pages, 2 figures. Accepted for publication in J. Phys.: Condens. Matter

We calculate the Josephson current across a plane interface separating dirty superconductors up to second order in the transparency of the junction. The leading contribution to the second-order correction is caused by the suppression of the superconducting order parameter near the interface. The ratio of the correction to the Josephson current in the first order is about D (T )/l , where D is the transparency of the junction, (T ) is the temperature-dependent coherence length, and l is the mean free path. This correction gives rise to the second harmonic in the current-phase relationship.

We suggest a parametrization of the quasiclassical equations of superconductivity which takes into account the boundary conditions on quasiclassical Green's functions. The resultant equations have a simple structure and permit numeric treatment of one-dimensional problems for arbitrary strength of the boundary potential. Both cases of absence and presence of the current through the system are discussed. We apply the technique to calculate the effect of the current through the interface with small reflectivity separating two superconductors. Contrary to the case of low transparency (conventional Josephson effect) the phase jump is not located at the interface. Rather it is distributed near the interface within characteristic range of the order of zero-temperature coherence length ${\ensuremath{\xi}}_{0}$ (clean limit) or mean free path l (dirty limit).

We show that the maximum penetration depth of the anomalous quasiclassical Green's function from a superconductor into an adjacent normal metal is directly related to the phase relaxation time τ ϕ. The latter describes normal-metal phase correlations between two electrons with opposite spins. In the presence of spin-dependent interactions this phase relaxation time differs from the one found in weak localization corrections to the conductivity. The Josephson current measurements in a SINIS-structure could be used to determine τ ϕ experimentally.

Photon-assisted electron transport for resonant tunneling has been investigated by using a current formula developed based on the nonequilibrium Green’s function technique. We have studied the external frequency dependence as well as the energy level position dependence for the resonant ac tunneling through the quantum dot coupled to two superconducting reservoirs.

We demonstrate that the two-particle corrections to the tunneling current in junctions between anisotropic superconductors lead to peculiarities in the differential conductance characteristics. These peculiarities are either jumps or logarithmic peaks.

Equations for the analogues of u and $v$ performing Bogoliubov transformation are derived in the case of anisotropic multiband superconductors. They are now represented by $n\ifmmode\times\else\texttimes\fi{}n$ matrices, where n is a number of bands relevant to superconducting pairing. We demonstrate that minimization of the ground-state energy does not fix all the parameters of canonical transformation at low temperatures, and thus additional minimization of the free energy due to the excited states is required.

Structures ofmagnetic field fluctuations in the HANBIT mirror device have been measured using a movable magnetic probe. The effects of the magnetic field and the RF power on the magnetic fluctuations have been studied. Electromagnetic plasma waves in low-pressure plasmas and high-pressure plasmas have been analyzed and the results indicates that sideband mode coupling is smaller in low-pressure plasmas. It is also found that the lower sideband coupling is enhanced at the resonance point, where the frequency of applied RF wave is similar to that of local ion cyclotron frequency, and a local stabilization of magnetic fluctuations is observed to occur there.

Phase of the transmission coefficient for a mesoscopic loop with Fano resonance has been investigated by using the scattering matrix method, for a model of an Aharonov-Bohm ring with a double barrier coupled to a $t$-stub resonator in one arm. It is found that the phase varies rapidly by \ensuremath{\pi} on the shoulder of a resonance peak. In addition, it is found that there is a sudden phase jump by $\ensuremath{\pi}$ near the tail of a resonance peak. Each resonance peak is found to return to the same phase via two processes; in one process, the phase shift by $\ensuremath{\pi}$ occurs rather smoothly through the excitation of the $h/2e$ oscillation near the resonance peak, and in the other process, the same amount of phase shift occurs very abruptly across the zero transmission of the resonator. These phase behaviors show some resemblance to the ones found in the recent phase measurement of a quantum dot via double-slit interference experiment.