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In this manuscript the dispersion relations of streaming instabilities, by using the unique property (neutralized in charge and current by default) of plasma shells colliding, have been generalized and studied. This interesting property for interpenetrating beams enables one to find the general dispersion relations without any restrictions used in the previous works in this area. In our previous work [H. Mehdian et al., ApJ. 801, 89 (2015)], employing the plasma shell concept and boost frame method, the general dispersion relation for filamentation instability has been derived in the relativistic classical regime. But in this paper, using the above mentioned concepts, the general dispersion relations (for each of streaming instabilities, filamentation, twostream and multi-stream) in the non-relativistic quantum regime have been derived by employing the quantum fluid equations together with Maxwell equations. The derived dispersion relations enable to describe any arbitrary system of interacting two and three beams, justified neutralization condition, by choosing the inertial reference frame embedded on the one of the beams. Furthermore, by the numerical and analytical study of these dispersion relations, many new features of streaming instabilities (E.g. their cut-off wave numbers and growth rates) in terms of all involved parameters have been illustrated. The obtained results in this paper can be used to describe many astrophysical systems and laboratory astrophysics setting, such as collision of non-parallel plasma shells over a background plasma or the collision of three neutralized plasma slabs, and justifying the many plasma phenomena such as particle accelerations and induced fields. [ABSTRACT FROM AUTHOR]

This paper discusses the spatial resolution that is required to study inhomogeneous, low-temperature plasmas and is based on a review of low-temperature plasma electron kinetics and methods for probe measurements of electron energy distribution functions (EEDFs). It is stated that EEDFs can be extracted from probe measurements by applying an appropriate probe theory. The Druyvesteyn formula is most commonly used for this extraction and has been used in numerous publications, but more general theory can be used for a wider range of gas pressures. It is demonstrated that the Druyvesteyn formula can be obtained from the general theory as a limiting case. This paper justifies the application of wall probes in plasma studies of an energetic part of EEDFs. This justification is made for an idealized probe. We briefly review the methods for studying anisotropic plasmas and their usefulness in plasma research. It is demonstrated that to determine anisotropic electron energy distribution functions, a planar, one-sided probe is most convenient. [ABSTRACT FROM AUTHOR]

Thermonuclear inertial confinement fusion plasmas confined by a heavy metal shell may be subject to the mixing of metal into the gas with a resulting degradation of fusion yield. Classical plasma diffusion driven by a number of gradients can provide a physical mechanism to produce atomic mix, possibly in concert with complex hydrodynamic structures and/or turbulence. This paper gives a derivation of the complete dissipative plasma hydrodynamics equations from kinetic theory, for a binary ionic mixture plasma consisting of electrons, e, a light (hydrogenic gas) ion species, i, and a heavy, high Z¡ plasma metal species, ¡. A single mean ionization state for the heavy metal, Z¡, is assumed to be provided by some independent thermodynamic model of the heavy metal Z¡ = Z¡ (ni, n¡, Te). The kinetic equations are solved by a generalized Chapman-Enskog expansion that assumes small Knudsen numbers for all species: NKe = ke/L 1, NKi = ki/L 1. The small electron to ion mass ratio, me/mi 1, is utilized to account for electron-ion temperature separation, Te = Ti, and to decouple the electron and ion transport coefficient calculations. This produces a well ordered perturbation theory for the electrons, resulting in the well known "Spitzer" problem of Spitzer and collaborators and solved independently by Braginskii. The formulation in this paper makes clear the inherent symmetry of the transport and gives an analytic solution for all values of the effective charge Zeff, including Zeff < 1. The electron problem also determines the ambipolar electric field and the "thermal forces" on both ion species that are needed for the ion kinetic solution. The ion transport problem makes use of the small mass ratio between ion species, mi/m¡ 1, to identify an "ion Spitzer problem" that is mathematically identical to that for the electrons but with different thermodynamic forces. The ionic scattering parameter, A¡ = n¡Z/ni, replaces the Ze¡¡ of the electron problem, but has an extended domain, 0 < A¡ < i, to cover all mixture fractions from the pure gas to the pure metal plasma. The extension of the Spitzer problem to include this extended domain is given in this work. The resulting transport equations for the binary gas-metal plasma mixture are complete and accurate through second order. All transport coefficients are provided in analytic form. [ABSTRACT FROM AUTHOR]

In this work involving an atmospheric dielectric barrier discharge system, the feasibility of independence control of key plasma parameters through strategic modulation of applied dual-frequency excitation sources is demonstrated. In this paper, a one-dimensional fluid model with semi-kinetic method has been used to investigate the discharge properties of atmospheric dielectric barrier discharge by using 200 kHz/13.56 MHz excitations. Bearing good consistency and coherence with experimental results, the electrical characteristics and typical electron dynamics are studied numerically. It is revealed that the application of the high frequency excitation can restrain the increment of the low frequency current component and is effective in preventing the discharge from transitioning to a filamentary mode. This method then suggests and enables possible approaches to obtain discharges with good stability in described DBD systems. [ABSTRACT FROM AUTHOR]

Previous DIII-D research has identified the presence of a multimodal plasma response to perturbations with toroidal periodicity equal to 2, with kink-like phenomenology of the plasma response in the low field side mid-plane and a resonant-like behavior in the high field side midplane. In this paper, we extend that initial midplane observation with the first detailed analysis of the poloidal structure of the plasma response as a function of the poloidal spectrum of the applied n = 2 perturbation and compare it to predictions made with the linear magnetohydrodynamics code MARS-F, confirming an overall good agreement. Singular value decomposition analysis of both the experimental data and the modeling identifies two distinct poloidal mode structures, one peaking at the low field side midplane and one peaking at θ ± 50°, each with a well-defined dependence on the poloidal spectrum of the applied perturbation. A study of the effect that βN has on the two modes confirms the kink-like phenomenology of the plasma response that dominates the low field side mid-plane, shows that the behavior previously associated with the high field side is observable at all poloidal angles, and highlights that the mode dominant at low βN becomes the secondary one at high βN. Detailed analysis of the high field side response is presented as well, suggesting the presence of a third mode linked to the presence of non-linear effects corresponding to particular poloidal spectra of the applied perturbation. [ABSTRACT FROM AUTHOR]

The Sagdeev pseudo-potential approach has been employed extensively in theoretical studies to determine large-amplitude (fully) nonlinear solutions in a variety of multi-species plasmas. Although these solutions are repeatedly considered as solitary waves (and even solitons), their temporal stability has never been proven. In this paper, a numerical study of the Vlasov-Poisson system is made to follow their temporal evolution in the presence of numerical noise and thereby test their long-time propagation stability. Considering the ion-acoustic regime, both constituents of the plasma, i.e., electrons and ions are treated following their distribution functions in these sets of fully-kinetic simulations. The findings reveal that the stability of the Sagdeev solution depends on a combination of two parameters, i.e., velocity and trapping parameter. It is shown that there exists a critical value of trapping parameter for both fast and slow solutions which separates stable from unstable solutions. In the case of stable solutions, it is shown that these nonlinear structures can propagate for long periods, which confirms their status as solitary waves. Stable solutions are reported for both Maxwellian and Kappa distribution functions. For unstable solutions, it is demonstrated that the instability causes the Sagdeev solution to decay by emitting ion-acoustic wave-packets on its propagation trail. The instability is shown to take place in a large range of velocities and even for Sagdeev solutions with a velocity much higher than the ion-sound speed. Besides, in order to validate our simulation code, two precautionary measures are taken. First, the well-known effect of the ion dynamics on a stationary electron hole solution is presented as a benchmarking test of the approach. Second, In order to verify the numerical accuracy of the simulations, the conservation of energy and entropy is presented. [ABSTRACT FROM AUTHOR]

Langmuir probe diagnostic on magnetic plasma devices often encounters more challenges in data processing than in non-magnetized plasmas, the latest itself being far from simple. In this paper, a theory of particle collection by a probe at the plasma potential in collisionless weakly ionized plasmas is constructed, accounting for velocities distributed according to the Maxwell equation and different mechanisms of particle collection depending on their speed. Experimental validation of the presented theory has been done with 2 cylindrical probes (rpr = 75 μm and Lpr = 1 cm and rpr = 0.5 mm and Lpr = 1 cm) parallel to B → on a linear plasma device Aline, with magnetic fields of 0.0024–0.1 T and plasma densities of 1015–1017 m−3 in helium. Cylindrical probe measurements are compared to data from a planar probe perpendicular to the magnetic field, and the results for electron density, temperature, and plasma potential are presented. The introduced theory is initially constructed for a cylindrical probe but is applicable to various probe sizes, shapes, and orientations. Alongside the main subject, a number of associated issues are addressed with different details: a probe design issue relative to the magnetized environment, the “intersection” method of plasma potential evaluation, and the robustness of the conventional “1st derivative” method, a current bump near the plasma potential, lower limit for electron temperature estimation, and self-consistent calculation of electron temperature and density. [ABSTRACT FROM AUTHOR]

The paper describes the behaviour of plasma within a MA plasma-focus with a novel electrode configuration, in which the anode and anti-anode were both equipped with conical tips. This configuration was applied to test the possibility of reducing the pinch axial dimensions during the radial compression of a current sheath. It made it possible to strengthen a dense plasma jet near the anode end, which ejected plasma into a bigger plasmoidal structure formed in the central pinch region. It did not allow forming an opposite anti-anode jet and stopped the axial motion of this structure. In plasma focus discharges with the deuterium filling, the decay of the anode jet and the corresponding plasmoid evolution were accompanied by the fusion-neutron production. Some results obtained with this configuration have also supported the hypothesis of the acceleration of fast electrons and ions at a release of the magnetic energy during magnetic reconnections in the organized dense plasma structures. [ABSTRACT FROM AUTHOR]

We study the viscosity of light charged particles in weakly ionized plasma with the power-law q-distributions using the generalized Boltzmann equation of transport and the motion equation of hydrodynamics. The nonequilibrium plasma variables are considered to be space inhomogeneous and without magnetic field. We derive the expressions of the viscosity coefficients of electrons and ions in the q-distributed plasma, including the first and the second viscosity coefficients. It is shown that these new viscosity coefficients depend strongly on the q-parameters, and when we take q → 1, they perfectly return to those in the plasma with a Maxwellian distribution. The discussions presented in this paper can also be applied to the plasmas with the kappa-distributions. [ABSTRACT FROM AUTHOR]

The collective response of the plasma medium is well known and has been explored extensively in the context of dusty plasma medium. On the other hand, the individual particle response associated with the collisional character giving rise to the dissipative phenomena has not been explored adequately. In this paper, two-dimensional molecular dynamics simulation of dust particles interacting via Yukawa potential has been considered. It has been shown that disturbances induced in a dust crystal elicit both collective and single particle responses. Generation of a few particles moving at speeds considerably higher than acoustic and/or shock speed (excited by the external disturbance) is observed. This is an indication of a single particle response. Furthermore, as these individual energetic particles propagate, the dust crystal is observed to crack along their path. Initially when the energy is high, these particles generate secondary energetic particles by the collisional scattering process. However, ultimately as these particles slow down they excite a collective response in the dust medium at secondary locations in a region which is undisturbed by the primary external disturbance. The condition when the cracking of the crystal stops and collective excitations get initiated has been identified quantitatively. The trailing collective primary disturbances would thus often encounter a disturbed medium with secondary and tertiary collective perturbations, thereby suffering significant modification in its propagation. It is thus clear that there is an interesting interplay (other than mere dissipation) between the single particle and collective response which governs the dynamics of any disturbance introduced in the medium. [ABSTRACT FROM AUTHOR]

In this paper, the focusing effect on backward Raman amplification in plasma is investigated. A fluid model, used to simulate the backward Raman amplification and including the relativistic, ponderomotive, and thermal self-focusing and the mutual-focusing effect simultaneously, is proposed and investigated. The focusing effect is shown to severely distort the profile of the seed when the seed intensity was as high as 10 17 W/cm2. Reducing the plasma density can relax the focusing effect, but at the cost of decreasing the amplification efficiency. Changing the profile of the seed has a limited effect on mitigating the focusing effect. A Gaussian profile of the pump and a defocusing shape of the plasma density seem to be an effective way to mitigate the focusing effect without decreasing the amplification efficiency. [ABSTRACT FROM AUTHOR]

Experiments on Stimulated Raman Backscattering (SRBS) in plasma have demonstrated significantly higher energy conversion in a double-pass amplifier where the laser pulses go through the plasma twice compared with a single-pass amplifier with double the plasma length of a single pass. In this paper, the improvement in understanding recent experimental results is presented by considering quite in detail the effects of plasma heating on the modeling of SRBS. Our simulation results show that the low efficiency of single-pass amplifiers can be attributed to Landau damping and the frequency shift of Langmuir waves. In double-pass amplifiers, these issues can be avoided, to some degree, because pump-induced heating could be reduced, while the plasma cools down between the passes. Therefore, double-pass amplifiers yield considerably enhanced energy transfer from the pump to the seed, hence the output pulse intensity. [ABSTRACT FROM AUTHOR]

In this paper, we have studied linear and nonlinear propagation of electron acoustic waves (EAWs) comprising cold and hot populations in which the ions form the neutralizing background. The hot electrons have been assumed to follow the generalized ( r , q ) distribution which has the advantage that it mimics most of the distribution functions observed in space plasmas. Interestingly, it has been found that unlike Maxwellian and kappa distributions, the electron acoustic waves admit not only rarefactive structures but also allow the formation of compressive solitary structures for generalized ( r , q ) distribution. It has been found that the flatness parameter r , tail parameter q , and the nonlinear propagation velocity u affect the propagation characteristics of nonlinear EAWs. Using the plasmas parameters, typically found in Saturn's magnetosphere and the Earth's auroral region, where two populations of electrons and electron acoustic solitary waves (EASWs) have been observed, we have given an estimate of the scale lengths over which these nonlinear waves are expected to form and how the size of these structures would vary with the change in the shape of the distribution function and with the change of the plasma parameters. [ABSTRACT FROM AUTHOR]

The physical process of electrical explosion of wires in vacuum is featured with the surface discharge along the wire, which generates the corona plasma layer and terminates the Joule heating of the wire core. In this paper, a fiber-array probe was designed to directly measure the radiation of surface arc with spatial and temporal resolution. The radiation of the exploding wire was casted to the section of an optical-fiber-array by a lens and transmitted to PIN diodes and finally collected with an oscilloscope. This probe enables direct diagnostics of the evolution of surface discharge with high temporal resolution and certain spatial resolution. The radiation of a tungsten wire driven by a positive current pulse was measured, and results showed that surface discharge initiates near the cathode and propagates toward the anode with a speed of 7.7 ± 1.6 mm/ns; further estimations showed that this process is responsible for the "conical" structure of the exploding wire. [ABSTRACT FROM AUTHOR]

The gyrokinetic magnetohydrodynamic (MHD) equations, related to the recent paper by W. W. Lee ["Magnetohydrodynamics for collisionless plasmas from the gyrokinetic perspective," Phys. Plasmas 23, 070705 (2016)], and their associated equilibria properties are discussed. This set of equations consists of the time-dependent gyrokinetic vorticity equation, the gyrokinetic parallel Ohm's law, and the gyrokinetic Ampere's law as well as the equations of state, which are expressed in terms of the electrostatic potential, ϕ, and the vector potential, A, and support both spatially varying perpendicular and parallel pressure gradients and the associated currents. The corresponding gyrokinetic MHD equilibria can be reached when ϕ→0 and A becomes constant in time, which, in turn, gives ∇.(J∥+J⊥)=0 and the associated magnetic islands, if they exist. Examples of simple cylindrical geometry are given. These gyrokinetic MHD equations look quite different from the conventional MHD equations, and their comparisons will be an interesting topic in the future. [ABSTRACT FROM AUTHOR]

The shear flow in dust dynamics driven waves in combination with the dust-neutral drag is studied in a plasma comprising of ions, electrons, and dust. Non-thermal population of ions is considered, which has been observed by many satellite missions. It is found that the dissipative instability produced by dust sheared flow and dust-neutral drag gets modified by the presence of nonthermal ions. It is found that the dissipative instability enhances for the Cairns distribution, whereas the kappa distribution arrests the growth of this instability. In the nonlinear regime, the formation of vortices in the system is studied. It is found that the nonthermal population of ions significantly alters these structures in comparison with their Maxwellian counterpart. The results obtained in this paper may have relevance in the planetary magnetospheres where the dust particles are present and non-Maxwellian distribution of particles have been observed by Freja and Viking satellites. [ABSTRACT FROM AUTHOR]

The effects of a collector plasma in a relativistic backward wave oscillator are investigated using a numerical simulation. Analyzing mainly the diffusion process, the results show a fast plasma diffusion occurring as one of the most important reasons for pulse shortening. In this process, the fast plasma affects the modulation of the intense relativistic electron beams, leads to drifting of the microwave frequency, absorbs gigawatts of microwave power, and finally causes pulse shortening. Here, the mechanism underpinning fast diffusion is mainly attributed to the standing wave pattern of the microwave field in the interaction region and the space charge effect. This paper reveals the change in the system after pulse shortening caused by fast diffusion and suggests a measure to control this process by restraining the collector plasma. [ABSTRACT FROM AUTHOR]

In this paper, the effect of the wiggler magnetic field strength on the self-focusing of an intense laser pulse propagating through a magnetized non-Maxwellian plasma is studied. By using a relativistic fluid model, a non-linear equation describing the spot-size of the laser pulse for right- and left-hand polarizations has been derived. The evaluation of the spot-size in the self-focusing of laser pulse with the respect to the kind of polarization is investigated. Besides, the effects of wiggler magnetic field and a non-Maxwellian distribution of charge density on the evolution of the laser spot-size have been discussed. The results show that in the right-hand polarization, the existence of superthermal particles and wiggler magnetized field simultaneously cause improvement in the self-focusing quality. In addition, for the left-hand polarization, the self-focusing in the presence of wiggler field increases with an increase in the ki. Furthermore, the self-focusing decreases with an increase in the wiggler amplitudes for the left-hand polarization. Moreover, it is observed that an increase in the normalized laser frequency leads to an increase in the variation in the laser spot-size, and then the laser pulse becomes more focused. [ABSTRACT FROM AUTHOR]

Nonlinear interplay between the finite frequency inertial Alfvén wave and slow magnetosonic wave for low β-plasma (β ⪡ me/mi) has been studied in the paper. The governing equation of slow magnetosonic wave has been derived in the presence of ponderomotive force associated with the finite frequency inertial Alfvén wave. A numerical simulation has been performed for the set of dimensionless governing equations representing finite frequency inertial Alfvén wave and slow magnetosonic wave for the parameters of auroral region. The localized structures and turbulence spectrum have been studied for the different angles of propagation (like θ = 5°, 25°, 45°, 75°) of slow magnetosonic wave. From the results, it has been observed that the localization becomes labyrinthine and varies with the change in the angle of propagation for the slow magnetosonic wave. Further, the spectral index follows the (~k-3:8) for θ = 5°, (~k-4:05) for θ = 25°, (~k-4:2) for θ= 45°, and (~k-4:35) for θ = 75°. Hence, one can conclude that the variation in the angle of propagation of slow magnetosonic wave affects the localization and spectral scaling. This variation may be responsible for the heating and acceleration of the plasma species in auroral region. The relevancy of the simulation results have been shown with the observation recorded by the spacecrafts such as FAST, Heos 2, Hawkeye 1, and Dynamics Explorer 1. [ABSTRACT FROM AUTHOR]

Experimental observations of a new regime of whistler propagation in the laboratory are reported in this paper. The experiments are carried out in a large laboratory unbound uniform plasma with a density of ne ~ 109-1011 cm-3 and a magnetic field of 1-20G. Studies are performed in the electron magnetohydrodynamic regime, which is governed by electron dynamics with Le⪡L⪡Li and τci⪢τ ⪢ τce, where L and τ are the spatial and temporal scale lengths of the perturbations, Le and Li the electron and ion Larmor radii, respectively, and τci and τce the temporal scales corresponding to the ion gyrofrequency and electron gyrofrequency, respectively. The complete topology of the perturbed wave magnetic field is unravelled by mapping it on a two dimensional grid over repeated plasma shots. It is observed that the excited waves are elongated whistlers in the propagation direction. However, in the perpendicular direction, the extent is limited to scale lengths of the order of natural scale length of plasma, i.e., the skin depth (~c/ωpe), rather than being oblique as predicted by theory and observed in other experiments. The wave shows a feeble resonance cone at an angle of ~10° but no obliqueness. Also, the secondary induction, which helps the wave to propagate further into the plasma, does not manifest within the spatial scale lengths characteristic to this regime. However, the wave is still able to maintain the whistler speed calculated for the given plasma and pulsed current parameters. It is speculated that the natural scale length (skin depth) and in turn the electron inertia may play a significant role, leading to the observed results. A physical model is also presented that could possibly explain the observed phenomena. [ABSTRACT FROM AUTHOR]

One of the best ways to get information about plasma and interactions within it, is the study on visible light emitted from plasma. Detection of the emission spectrum from plasma leads to identify the spectral lines of ions and impurities inside the plasma and measurement of all related parameters to ion flux such as velocity and temperature. The first measurement of impurities into the IR-T1 tokamak plasma is done by spectroscopic technique. The CCD-based spectrometer device with the wavelength range of 400-550 nm is used to detection the spectrum emitted from the plasma. The impurities into the plasma in the intended wavelength range are identified. Furthermore, the Doppler broadening of the most intense peaks of impurities and their temperatures are measured. The methods in this paper can be used on all fusion devices. [ABSTRACT FROM AUTHOR]

In this paper, we have studied the influence of magnetic quantization of orbital motion of the electrons on the profile of linear and nonlinear ion-acoustic waves, which are propagating in the ultra-relativistic dense magneto quantum plasmas. We have employed both Thomas Fermi and Quantum Magneto Hydrodynamic models (along with the Poisson equation) of quantum plasmas. To investigate the large amplitude nonlinear structure of the acoustic wave, Sagdeev-Pseudo-Potential approach has been adopted. The numerical analysis of the linear dispersion relation and the nonlinear acoustic waves has been presented by drawing their graphs that highlight the effects of plasma parameters on these waves in both the linear and the nonlinear regimes. It has been noticed that only supersonic ion acoustic solitary waves can be excited in the above mentioned quantum plasma even when the value of the critical Mach number is less than unity. Both width and depth of Sagdeev potential reduces on increasing the magnetic quantization parameter η. Whereas the amplitude of the ion acoustic soliton reduces on increasing η, its width appears to be directly proportional to η. The present work would be helpful to understand the excitation of nonlinear ion-acoustic waves in the dense astrophysical environments such as magnetars and in intense-laser plasma interactions. [ABSTRACT FROM AUTHOR]

When weakly collisional plasmas have locally trapped particle populations, perturbations to the plasma equilibrium (such as waves or static field-errors) can induce phase-space discontinuities in the particle distribution function that strongly enhance entropy production, plasma loss and wave damping via superbanana transport. This paper presents a simple version of this superbanana transport process, wherein a plasma is heated as it is slowly forced back and forth across a squeeze potential (at a frequency ω that is small compared with the particle bounce frequency). The squeeze potential traps low-energy particles on either side of the squeeze, but particles with higher energy can pass through it. Trapped and passing particles have different responses to the forcing, causing a collisionless discontinuity in the distribution function at the separatrix between the trapped and passing particles. Expressions for both the adiabatic and non-adiabatic distribution functions are presented and the heating rate caused by collisional broadening of the separatrix discontinuity is derived. The heating rate is proportional to √ ν ω , provided that ν ⪡ ω, where ν is the collisionrate (i.e., the √ ν regime of superbanana theory). [ABSTRACT FROM AUTHOR]

Helicon wave heated plasmas are much more efficient in terms of ionization per unit power consumed. A permanent magnet based compact helicon wave heated plasma source is developed in the Institute for Plasma Research, after carefully optimizing the geometry, the frequency of the RF power, and the magnetic field conditions. The HELicon Experiment for Negative ion-I source is the single driver helicon plasma source that is being studied for the development of a large sized, multi-driver negative hydrogen ion source. In this paper, the details about the single driver machine and the results from the characterization of the device are presented. A parametric study at different pressures and magnetic field values using a 13.56 MHz RF source has been carried out in argon plasma, as an initial step towards source characterization. A theoretical model is also presented for the particle and power balance in the plasma. The ambipolar diffusion process taking place in a magnetized helicon plasma is also discussed. [ABSTRACT FROM AUTHOR]

In this paper, we present an experimental study on the self-pulsing phenomenon in a flow-induced atmospheric pressure plasma jet (APPJ) in a hollow electrode configuration driven by dc voltage supply. The current-voltage curve, the typical waveforms of current and voltage of self-pulsing, the time-resolved images, and the repetition frequency were measured under different experimental conditions. The results show that the APPJ of a hollow electrode can sustain in a stable, repeatable self-pulsing regime. The waveform of the pulsed current is very stable with nearly constant rising time and decay time at different discharge averaged currents. Although the pulsing frequency increases linearly with the averaged current and the gas flow rate, it decreases with the electrode gap. An equivalent electric circuit consisting of a capacitor and two resistors was used to model the self-pulsing discharge plasma. The simulation results and the time-resolved images recorded using an ICCD camera show that the pulsed process of the hollow electrode APPJ contains the evolutions of gas breakdown, discharge development, and decay of a glow plasma. A weak discharge is maintained during the time interval between two pulses, indicating that the self-pulsing in this APPJ is a mode transition between glow and weak discharge. [ABSTRACT FROM AUTHOR]

Atmospheric pressure non-equilibrium plasmas have attracted significant attention and have been widely used to inactivate pathogens, yet the mechanisms underlying the interactions between plasma-generated species and bio-organisms have not been elucidated clearly. In this paper, reactive molecular dynamics simulations are employed to investigate the mechanisms of interactions between reactive oxygen plasma species (O, OH, and O2) and β-1,6-glucan (a model for the C. albicans cell wall) from a microscopic point of view. Our simulations show that O and OH species can break structurally important C-C and C-O bonds, while O2 molecules exhibit only weak, non-bonded interactions with β-1,6-glucan. Hydrogen abstraction from hydroxyl or CH groups occurs first in all bond cleavage mechanisms. This is followed by a cascade of bond cleavage and double bond formation events. These lead to the destruction of the fungal cell wall. O and OH have similar effects related to their bond cleavage mechanisms. Our simulation results provide fundamental insights into the mechanisms underlying the interactions between reactive oxygen plasma species and the fungal cell wall of C. albicans at the atomic level. [ABSTRACT FROM AUTHOR]

The post-arc dielectric recovery process has a decisive effect on the current interruption performance in a vacuum circuit breaker. The dissipation of residual plasma at the moment of current zero under the transient recovery voltage, which is the first stage of the post-arc dielectric recovery process and forms the post-arc current, has attracted many concerns. A one-dimensional particle-in-cell model is developed to simulate the measured post-arc current in the vacuum circuit breaker in this paper. At first, the parameters of the residual plasma are estimated roughly by the waveform of the post-arc current which is taken from measurements. After that, different components of the post-arc current, which are formed by the movement of charged particles in the residual plasma, are discussed. Then, the residual plasma density is adjusted according to the proportion of electrons and ions absorbed by the post-arc anode derived from the particle-in-cell simulation. After this adjustment, the post-arc current waveform obtained from the simulation is closer to that obtained from measurements. [ABSTRACT FROM AUTHOR]

Proton-driven plasma wakefield acceleration has been demonstrated in simulations to be capable of accelerating particles to the energy frontier in a single stage, but its potential is hindered by the fact that currently available proton bunches are orders of magnitude longer than the plasma wavelength. Fortunately, proton micro-bunching allows driving plasma waves resonantly. In this paper, we propose using a hollow plasma channel for multiple proton bunch driven plasma wakefield acceleration and demonstrate that it enables the operation in the nonlinear regime and resonant excitation of strong plasma waves. This new regime also involves beneficial features of hollow channels for the accelerated beam (such as emittance preservation and a uniform accelerating field) and long buckets of stable deceleration for the drive beam. The regime is attained at a proper ratio between plasma skin depth, driver radius, hollow channel radius, and micro-bunch period. [ABSTRACT FROM AUTHOR]

The coupling of the short wavelength ion temperature gradient mode (SWITG) and trapped electron mode (SWTEM) in the presence of impurity ions is numerically studied in tokamak plasmas. It is found that the coupling of SWITG and SWTEM modes is divided into hybrid and coexistent cases. The impurity ions always have stabilizing effects on the hybrid mode (namely, SWTE-ITG) with small ηi (ηi < 0.5), which is different from the conventional TE-ITG mode. In the lager ηi (ηi > 0.5) regime, the impurity ions with the density profiles peaked inwardly (outwardly) stabilize (destabilize) the SWTE-ITG mode. Another new finding in this paper is that the impurity ions stabilize the SWTEM mode independent of whether their density profile is peaked inwardly or outwardly. The result for the SWITG mode is similar to the SWTE-ITG mode in the lager ηi regime, except that the excitation of the SWTEM mode requires ηi higher than a certain threshold. In addition, the kθρs spectra, eigenmode structures, and the effects of different impurity ion species on the modes are discussed. [ABSTRACT FROM AUTHOR]

The radiation transfer in dynamic hohlraums on the PTS facility is preliminarily investigated in this paper. Simulation results show that as the accelerated wire-array plasma impacts onto the foam converter, energy thermalization takes place in a local interaction region near the boundary of the wirearray plasma and the foam converter, and then, high temperature radiation is gradually generated. Its transfer process largely depends on the radiation temperature and the mass density of the converter. When the mass ratio of the wire-array to the converter is near 1.0, the radiation temperature can be increased to about 120 eV with the PTS drive current. In this case, the radiation generated from the interaction region will quickly transfer to the center of the converter. The experimental end-on x-ray images present the overall process of radiation production and transfer of this kind of dynamic hohlraum. As the mass ratio is decreased, the radiation temperature will also be deceased, and the converter will become more opaque to the radiation. In the case of extremely low mass ratios such as lower than 0.3, the peak radiation temperature will be much lower than 100 eV, and the radiation transfers slowly to the interior of the converter and presents large non-uniformity, which is also observed in experiments on the PTS facility. [ABSTRACT FROM AUTHOR]

The Motional Stark Effect (MSE) diagnostic is a well established technique to infer the local internal magnetic field in fusion plasmas. In this paper, the existing forward model which describes the MSE data is extended by the Zeeman effect, fine-structure, and relativistic corrections in the interpretation of the MSE spectra for different experimental conditions at the tokamak ASDEX Upgrade. The contribution of the non-Local Thermodynamic Equilibrium (non-LTE) populations among the magnetic sub-levels and the Zeeman effect on the derived plasma parameters is different. The obtained pitch angle is changed by 3° ... 4° and by 0.5° ... 1° including the non-LTE and the Zeeman effects into the standard statistical MSE model. The total correction is about 4°. Moreover, the variation of the magnetic field strength is significantly changed by 2.2% due to the Zeeman effect only. While the data on the derived pitch angle still could not be tested against the other diagnostics, the results from an equilibrium reconstruction solver confirm the obtained values for magnetic field strength. [ABSTRACT FROM AUTHOR]

A recent publication [K. Lan et al., Phys. Plasmas 21, 010704 (2014)] proposed a spherical hohlraum with six laser entrance holes of octahedral symmetry at a specific hohlraum-to-capsule radius ratio of 5.14 for inertial fusion study, which has robust high symmetry during the capsule implosion and superiority on low backscatter without supplementary technology. This paper extends the previous one by studying the laser arrangement and constraints of octahedral hohlraum in detail. As a result, it has serious beam crossing at θL ⩽ 45°, and θL = 50° to 60° is proposed as the optimum candidate range for the golden octahedral hohlraum, here hL is the opening angle that the laser quad beam makes with the Laser Entrance Hole (LEH) normal direction. In addition, the design of the LEH azimuthal angle should avoid laser spot overlapping on hohlraum wall and laser beam transferring outside hohlraum from a neighbor LEH. The octahedral hohlraums are flexible and can be applicable to diverse inertial fusion drive approaches. This paper also applies the octahedral hohlraum to the recent proposed hybrid indirect-direct drive approach. [ABSTRACT FROM AUTHOR]

Doppler broadening of the 14 MeV DT and 2.45 MeV DD fusion neutron lines has long been our best measure of temperature in a burning plasma. At the National Ignition Facility (NIF), yields are high enough and our neutron spectrometers accurate enough that we see finer details of the peak shape. For example, we can measure the shift of the peak due to the bulk motion of the plasma, and we see indications of non-thermal broadening, skew, and kurtosis of the peak caused by the variations of temperature and fluid velocity during burn. We can also distinguish spectral differences among several lines of sight. This paper will review the theory of fusion neutron line shape, show examples of non-Gaussian line shapes and directional variations in NIF data, and describe detailed spectral shapes we see in radiation-hydrodynamics simulations of implosions. [ABSTRACT FROM AUTHOR]

This paper is devoted to studying how the inter-electrode distance affects the voltage drop across electrodes, the cathode sheath thickness, and the axial distribution of plasma parameters. The experiment demonstrates the simultaneous growth of both the voltage drop across the electrodes and the cathode sheath thickness when on increasing the gap the anode is moved away from the cathode while remaining in the negative glow. This effect is most clearly pronounced under low gas pressure and high current values when the negative glow length is large. The discharge axial structure dynamics is studied with the Langmuir probe technique and with the OOPIC Pro code. The inter-electrode gap growth with the current fixed is found to be accompanied by the plasma concentration increase in the negative glow. The positive plasma potential is shown to cause the current to the grounded anode to be transported by fast electrons accelerated in the cathode sheath. Moving the anode away from the cathode through the negative glow weakens the flow of fast electrons coming to the anode, thus decreasing the discharge current. In order to restore the discharge current, one has to increase the voltage across the electrodes, leading to the cathode sheath thickness increase and the plasma concentration growth in the negative glow. [ABSTRACT FROM AUTHOR]

In this paper, we develop an innovative approach to study the shock wave propagation using the Sagdeev potential method. We also present an analytical solution for Korteweg de Vries Burgers (KdVB) and modified KdVB equation families with a generalized form of the nonlinearity term which agrees well with the numerical one. The novelty of the current approach is that it is based on a simple analogy of the particle in a classical potential with the variable particle energy providing one with a deeper physical insight into the problem and can easily be extended to more complex physical situations. We find that the current method well describes both monotonic and oscillatory natures of the dispersive-diffusive shock structures in different viscous fluid configurations. It is particularly important that all essential parameters of the shock structure can be deduced directly from the Sagdeev potential in small and large potential approximation regimes. Using the new method, we find that supercnoidal waves can decay into either compressive or rarefactive shock waves depending on the initial wave amplitude. Current investigation provides a general platform to study a wide range of phenomena related to nonlinear wave damping and interactions in diverse fluids including plasmas. [ABSTRACT FROM AUTHOR]

The effect of finite magnetic field on the excitation, generation, and amplification of slow electromagnetic waves at THz frequency in a magnetized plasma waveguide with elliptical cross section is investigated. In configuration mentioned above, there are two electron beams with opposite directions as energy sources, and the role of magnetic field power on the appearance of the number of dispersion branches is analysed. It is shown that with increasing magnetic field, the field profiles of hybrid waves are increased in regions where the interaction of waves and electron beams are optimized. It is also shown that by applying the magnetic field, generation of THz frequencies can be easy to obtain in comparison to the unmagnetized case. In other words, by applying a finite magnetic field, better THz excitation occurs in the absence of high accelerating voltage. Increasing growth rate which can be achieved with increasing static magnetic field is also investigated. In this paper, because of high longitudinal velocity of electron beams, the effect of finite magnetic field on the fluctuations of electron beams is considered negligible. [ABSTRACT FROM AUTHOR]

This paper presents the study of a coupled system of equations for a laser beam and an ion acoustic wave (IAW) in a collisional plasma through numerical simulation. The pump beam has been perturbed by a periodic perturbation that leads to the nonlinear evolution of the laser beam. The filamentation of the laser beam has been found to change appreciably with varying perturbation number. It was observed that the frequency spectra of the IAW lie in the gigahertz (GHz) domain. For the sake of better understanding of the physical process involved, a simplified model has been developed. The model contains spatial harmonics (obtained through simulation) at different times, by which the time dependent localization of the beam has been investigated. [ABSTRACT FROM AUTHOR]

Based on the 3-dimensional Particle-In-Cell (PIC) code CHIPIC3D, with a new circuit boundary algorithm we developed, a conical magnetically insulated transmission line (MITL) with a 1.0-MV linear transformer driver (LTD) is explored numerically. The values of switch jitter time of LTD are critical parameters for the system, which are difficult to be measured experimentally. In this paper, these values are obtained by comparing the PIC results with experimental data of large diode-gap MITL. By decreasing the diode gap, we find that all PIC results agree well with experimental data only if MITL works on self-limited flow no matter how large the diode gap is. However, when the diode gap decreases to a threshold, the self-limited flow would transfer to a load-limited flow. In this situation, PIC results no longer agree with experimental data anymore due to the anode plasma expansion in the diode load. This disagreement is used to estimate the plasma expansion speed. [ABSTRACT FROM AUTHOR]

Anisotropic bi-Kappa distributed plasmas, as encountered in the solar wind and planetary magnetospheres, are susceptible to a variety of kinetic instabilities including the cyclotron instabilities driven by an excess of perpendicular temperature T⊥ > T∥ (where ∥, ⊥ denote directions relative to the mean magnetic field). These instabilities have been extensively investigated in the past, mainly limiting to a linear stability analysis. About their quasilinear (weakly nonlinear) development, some insights have been revealed by numerical simulations using PIC and Vlasov solvers. This paper presents a self-consistent analytical approach, which provides for both the electron and proton cyclotron instabilities an extended picture of the quasilinear time evolution of the anisotropic temperatures as well as the wave energy densities. [ABSTRACT FROM AUTHOR]

In the present paper, the Hea triplet line ratios (resonance, intercombination, and forbidden lines) are computed for photoionized plasmas, when the contributions of nearby satellite lines are taken into account. The computations have been carried out with our radiative-collisional code, RCF, which is based on the flexible atomic code. The calculations of these line ratios have been done for three materials, namely, silicon, magnesium, and neon. Our calculations are used to derive the plasma temperatures for several astronomical objects, where the spectra are emitted from photoionizing plasmas. It is shown that the incorporation of the satellite lines from doubly excited Li-like ions into the Heα triplet lines is necessary to obtain reliable temperature diagnostics for these astrophysical objects. [ABSTRACT FROM AUTHOR]

Helicon wave plasma demonstrates lots of advantages in high coupling efficiency, high density, and low magnetic field. However, the helicon wave plasma still meets challenges in applications of material deposition, surface treatment, and electromagnetic thrusters owing to the changeable coupled efficiency and the remarkable non-uniformity. In this paper, we explore the wave propagation characterization by the B-dot probe in various lengths of source tubes. We find that in a long source tube the standing wave appears under the antenna zone, while the traveling wave is formed out of the antenna region. The apparent modulation of wave amplitude is formed in upstream rather than in downstream of the antenna. In a short source tube, however, there is only standing wave propagation. [ABSTRACT FROM AUTHOR]

The present research is devoted to the problem of extraction grid choice for a single-grid source of bipolar ion-electron flow. The paper contains detailed reference information on ion and electron extraction characteristics of 10 different grids with broad range of parameters: aperture width (0.09-0.6 mm), grid transparency (0.19-0.51), thickness (0.036-0.5 mm), and with different aperture geometry. The grids with square, circular, and slit apertures were made with different technologies: laser cutting, welding, weaving, and electrolytic erosion. The general regularities of the ion and electron extraction from the single-grid source are experimentally researched for the cases of dc and RF extraction grid biasing. A conclusion has been made that the maximum extracted ion current at low ion energy (0-200 eV) does not significantly vary for all the grids and does not exceed half of the primary ion current from plasma multiplied by the optical grid transparency. The low-energy limit of efficient ion extraction has been discovered which cannot be overcome by the aperture narrowing. A conclusion is made that the RF extraction mode is superior for all the researched grids since it is characterized by higher extracted ion current at any acceleration voltage for any grid with much more simple and smooth extraction curves behavior in comparison to the dc case as well as absence of arcing, jumps, and hysteresis of the measured curves at any RF voltages. The unique ability of the RF biased single-grid source of simultaneous ion/electron emission has been studied. The measured maximal attainable ion beam current compensation ratio is always sufficiently higher than 1 and typically varies in the range 2-6. The results obtained in the present paper demonstrate prospective of the single-grid source in space thruster applications and in modern technologies, particularly for ion beam processing of wide bandgap semiconductor devices such as GaN and SiC transistors due to inherent precise beam neutralization. [ABSTRACT FROM AUTHOR]

In the present paper, a scheme for generation of terahertz (THz) radiation in electron-neutral collisional plasma based on beating of two Gaussian laser array beams has been proposed. It is shown that the efficiency of THz radiation based on the Gaussian laser array beams can be enhanced drastically in comparison with the efficiency of THz radiation based on the Gaussian one. Furthermore, the producing THz radiation by the Gaussian laser array beams, which has an exclusive field profile, is affected by some array structure parameters. It can also be used to overcome the negative consequences of electron neutral collisions in plasma, which may be occurring in the THz radiation generation process. Optimizing the collisional plasma, laser beams and array structure parameters, THz radiation efficiency up to 0.07% can be obtained in our scheme which is about three times greater than the maximum efficiency obtained for standard (single) Gaussian laser beam. Also, considering the electrostatic energy channel in solving the THz wave equation, and reduction of THz radiation efficiency to 0.054%, in this assumption, the ratio between the efficiency of Gaussian laser array beams and standard Gaussian laser beam remained unchanged. [ABSTRACT FROM AUTHOR]

The detection limit for helium (He) partial pressure monitoring via the Penning discharge optical emission diagnostic, mainly used for tokamak divertor effluent gas analysis, is shown here to be possible for He concentrations down to 0.1% in predominantly deuterium effluents. This result from a dedicated laboratory study means that the technique can now be extended to intrinsically (non-injected) He produced as fusion reaction ash in deuterium-tritium experiments. The paper also examines threshold ionization mass spectroscopy as a potential backup to the optical technique, but finds that further development is needed to attain with plasma pulse-relevant response times. Both these studies are presented in the context of continuing development of plasma pulse-resolving, residual gas analysis for the upcoming JET deuterium-tritium campaign (DTE2) and for ITER. [ABSTRACT FROM AUTHOR]

The Prototype Material Plasma Exposure eXperiment (Proto-MPEX) at Oak Ridge National Laboratory (ORNL) is a precursor linear plasma device to the Material Plasma Exposure eXperiment (MPEX), which will study plasma material interactions (PMIs) for future fusion reactors. This paper will discuss the initial steps performed towards completing a power balance on Proto-MPEX to quantify where energy is lost from the plasma, including the relevant diagnostic package implemented. Machine operating parameters that will improve Proto-MPEX's performance may be identified, increasing its PMI research capabilities. [ABSTRACT FROM AUTHOR]

A Synthetic Diagnostics Platform (SDP) for fusion plasmas has been developed which provides state of the art synthetic reflectometry, beam emission spectroscopy, and Electron Cyclotron Emission (ECE) diagnostics. Interfaces to the plasma simulation codes GTC, XGC-1, GTS, and M3D-C1 are provided, enabling detailed validation of these codes. In this paper, we give an overview of SDP's capabilities, and introduce the synthetic diagnostic modules. A recently developed synthetic ECE Imaging module which self-consistently includes refraction, diffraction, emission, and absorption effects is discussed in detail. Its capabilities are demonstrated on two model plasmas. The importance of synthetic diagnostics in validation is shown by applying the SDP to M3D-C1 output and comparing it with measurements from an edge harmonic oscillation mode on DIII-D. [ABSTRACT FROM AUTHOR]

In this paper, we report on the core plasma evolution during the rotation of coherent modes in a magnetized plasma column. The study makes use of an original tomographic diagnostic based on a single sensor. The experimental observations demonstrate that the mode shape is constant during the plasma rotation, therefore confirming an a priori assumption of single position measurements. The experimental set-up and the numerical inversion method used to interpret the data are presented. The results are then compared to two-dimensional probe measurements to assess their perturbative character and to give further details on the mode characteristics. A π/2 phase shift between the electrostatic potential and density perturbation is evidenced. [ABSTRACT FROM AUTHOR]

In this paper, an integrated experimental system is established to study the influence of deposited energy on the intensity of the shock wave induced by underwater pulse discharge. Considering the time varying behavior of the arc, the calculation methods of the deposited energy into the plasma channel and the average arc resistance are proposed and presented. The effect of the breakdown process on the deposited energy and the shock wave is analyzed. It can be concluded that the shock wave intensity can be improved by depositing more energy in the first half oscillation period and increasing the arc resistance. It is also found that the energy deposition and the shock wave intensity are significantly influenced by the breakdown time delay and the shape of the initial plasma channel. [ABSTRACT FROM AUTHOR]

This paper covers calculation of radial distribution functions, specific energy, and static electrical conductivity of CH2 plasma in the two-temperature regime. The calculation is based on the quantum molecular dynamics, density functional theory, and the Kubo-Greenwood formula. The properties are computed at 5 kK ≤Ti≤Te≤40 kK and ρ=0.954 g/cm3 and depend severely on the presence of chemical bonds in the system. Chemical compounds exist at the lowest temperature Ti=Te=5 kK considered; they are destroyed rapidly at the growth of Ti and slower at the increase of Te. A significant number of bonds are present in the system at 5 kK ≤Ti≤Te≤10 kK. The destruction of bonds correlates with the growth of specific energy and static electrical conductivity under these conditions. [ABSTRACT FROM AUTHOR]

Edge plasmas present a few challenges for gyrokinetic simulations that are absent in tokamak cores. Among them are large fluctuation amplitudes and plasma-wall interactions in the open field line region. In this paper, the widely used core turbulence code GENE, which employs a δf-splitting technique, is extended to simulate open systems with large electrostatic fluctuations. With inclusion and proper discretization of the parallel nonlinear term, it becomes equivalent to a full-f code and the δf-splitting causes no fundamental difficulty in handling large fluctuations. The loss of particles to the wall is accounted for by using a logical sheath boundary, which is implemented in the context of a finite-volume method. The extended GENE code is benchmarked for the well-established one-dimensional parallel transport problem in the scrape-off layer during edge-localized modes. The parallel heat flux deposited onto the divertor target is compared with previous simulation results and shows good agreement. [ABSTRACT FROM AUTHOR]