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1
Zhang, Yanzeng, und Xian-Zhu Tang. „On the collisional damping of plasma velocity space instabilities“. Physics of Plasmas 30, Nr. 3 (März 2023): 030701. http://dx.doi.org/10.1063/5.0136739.
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For plasma velocity space instabilities driven by particle distributions significantly deviated from a Maxwellian, weak collisions can damp the instabilities by an amount that is significantly beyond the collisional rate itself. This is attributed to the dual role of collisions that tend to relax the plasma distribution toward a Maxwellian and to suppress the linearly perturbed distribution function. The former effect can dominate in cases where the unstable non-Maxwellian distribution is driven by collisionless transport on a timescale much shorter than that of collisions, and the growth rate of the ideal instability has a sensitive dependence on the distribution function. The whistler instability driven by electrostatically trapped electrons is used as an example to elucidate such a strong collisional damping effect of plasma velocity space instabilities, which is confirmed by first-principles kinetic simulations.
2
Zhang, Yanzeng, Yuzhi Li, Bhuvana Srinivasan und Xian-Zhu Tang. „Resolving the mystery of electron perpendicular temperature spike in the plasma sheath“. Physics of Plasmas 30, Nr. 3 (März 2023): 033504. http://dx.doi.org/10.1063/5.0132612.
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A large family of plasmas has collisional mean-free-path much longer than the non-neutral sheath width, which scales with the plasma Debye length. The plasmas, particularly the electrons, assume strong temperature anisotropy in the sheath. The temperature in the sheath flow direction ([Formula: see text]) is lower and drops toward the wall as a result of the decompressional cooling by the accelerating sheath flow. The electron temperature in the transverse direction of the flow field ([Formula: see text]) not only is higher but also spikes up in the sheath. This abnormal behavior of [Formula: see text] spike is found to be the result of a negative gradient of the parallel heat flux of transverse degrees of freedom ( qes) in the sheath. The non-zero heat flux qes is induced by pitch-angle scattering of electrons via either their interaction with self-excited electromagnetic waves in a nearly collisionless plasma or Coulomb collision in a collisional plasma, or both in the intermediate regime of plasma collisionality.
3
Fan, Kaixuan, Xueqiao Xu, Ben Zhu und Pengfei Li. „Kinetic Landau-fluid closures of non-Maxwellian distributions“. Physics of Plasmas 29, Nr. 4 (April 2022): 042116. http://dx.doi.org/10.1063/5.0083108.
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New kinetic Landau-fluid closures, based on the cutoff Maxwellian distribution, are derived. A special static case is considered (the frequency [Formula: see text]). In the strongly collisional regime, our model reduces to Braginskii's heat flux model, and the transport is local. In the weak collisional regime, our model indicates that the heat flux is non-local and recovers the Hammett–Perkins model while the value of the cutoff velocity approaches to infinity. We compare the thermal transport coefficient [Formula: see text] of Maxwellian, cutoff Maxwellian and super-Gaussian distribution. The results show that the reduction of the high-speed tail particles leads to the corresponding reduction of the thermal transport coefficient [Formula: see text] across the entire range of collisionality, more reduction of the free streaming transport toward the weak collisional regime. In the collisionless limit, [Formula: see text] approaches to zero for the cutoff Maxwellian and the super-Gaussian distribution but remains finite for Maxwellian distribution. [Formula: see text] is complex if the cutoff Maxwellian distribution is asymmetric. The [Formula: see text] approaches to different convergent values in both collisionless and strongly collisional limit, respectively. It yields an additional streaming heat flux in comparison with the symmetric cutoff Maxwellian distribution. Furthermore, due to the asymmetric distribution, there is a background heat flux [Formula: see text] though there is no perturbation. The derived Landau-fluid closures are general for fluid moment models, and applicable for the cutoff Maxwellian distribution in an open magnetic field line region, such as the scape-off-layer of Tokamak plasmas, in the thermal quench plasmas during a tokamak disruption, and the super-Gaussian electron distribution function due to inverse bremsstrahlung heating in laser-plasma studies.
4
Bret, Antoine, und Ramesh Narayan. „Density jump for parallel and perpendicular collisionless shocks“. Laser and Particle Beams 38, Nr. 2 (14.04.2020): 114–20. http://dx.doi.org/10.1017/s0263034620000117.
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AbstractIn a collisionless shock, there are no binary collisions to isotropize the flow. It is therefore reasonable to ask to which extent the magnetohydrodynamics (MHD) jump conditions apply. Following up on recent works which found a significant departure from MHD in the case of parallel collisionless shocks, we here present a model allowing to compute the density jump for collisionless shocks. Because the departure from MHD eventually stems from a sustained downstream anisotropy that the Vlasov equation alone cannot specify, we hypothesize a kinetic history for the plasma, as it crosses the shock front. For simplicity, we deal with non-relativistic pair plasmas. We treat the cases of parallel and perpendicular shocks. Non-MHD behavior is more pronounced for the parallel case where, according to MHD, the field should not affect the shock at all.
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YANG, Wei, Fei GAO und Younian WANG. „Conductivity effects during the transition from collisionless to collisional regimes in cylindrical inductively coupled plasmas“. Plasma Science and Technology 24, Nr. 5 (13.04.2022): 055401. http://dx.doi.org/10.1088/2058-6272/ac56ce.
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Abstract A numerical model is developed to study the conductivity effects during the transition from collisionless to collisional regimes in cylindrical inductively coupled argon plasmas at pressures of 0.1–20 Pa. The model consists of electron kinetics module, electromagnetics module, and global model module. It allows for self-consistent description of non-local electron kinetics and collisionless electron heating in terms of the conductivity of homogeneous hot plasma. Simulation results for non-local conductivity case are compared with predictions for the assumption of local conductivity case. Electron densities and effective electron temperatures under non-local and local conductivities show obvious differences at relatively low pressures. As increasing pressure, the results under the two cases of conductivities tend to converge, which indicates the transition from collisionless to collisional regimes. At relatively low pressures the local negative power absorption is predicted by non-local conductivity case but not captured by local conductivity case. The two-dimensional (2D) profiles of electron current density and electric field are coincident for local conductivity case in the pressure range of interest, but it roughly holds true for non-local conductivity case at very high pressure. In addition, an effective conductivity with consideration of non-collisional stochastic heating effect is introduced. The effective conductivity almost reproduces the electron density and effective electron temperature for the non-local conductivity case, but does not capture the non-local relation between electron current and electric field as well as the local negative power absorption that is observed for non-local conductivity case at low pressures.
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McCubbin, Andrew J., Gregory G. Howes und Jason M. TenBarge. „Characterizing velocity–space signatures of electron energization in large-guide-field collisionless magnetic reconnection“. Physics of Plasmas 29, Nr. 5 (Mai 2022): 052105. http://dx.doi.org/10.1063/5.0082213.
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Magnetic reconnection plays an important role in the release of magnetic energy and consequent energization of particles in collisionless plasmas. Energy transfer in collisionless magnetic reconnection is inherently a two-step process: reversible, collisionless energization of particles by the electric field, followed by collisional thermalization of that energy, leading to irreversible plasma heating. Gyrokinetic numerical simulations are used to explore the first step of electron energization, and we generate the first examples of field–particle correlation signatures of electron energization in 2D strong-guide-field collisionless magnetic reconnection. We determine these velocity space signatures at the x-point and in the exhaust, the regions of the reconnection geometry in which the electron energization primarily occurs. Modeling of these velocity–space signatures shows that, in the strong-guide-field limit, the energization of electrons occurs through bulk acceleration of the out-of-plane electron flow by the parallel electric field that drives the reconnection, a non-resonant mechanism of energization. We explore the variation of these velocity–space signatures over the plasma beta range [Formula: see text]. Our analysis goes beyond the fluid picture of the plasma dynamics and exploits the kinetic features of electron energization in the exhaust region to propose a single-point diagnostic, which can potentially identify a reconnection exhaust region using spacecraft observations.
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Hong, Young-Hun, Tae-Woo Kim, Ju-Ho Kim, Yeong-Min Lim, Moo-Young Lee und Chin-Wook Chung. „Experimental investigation on the hysteresis in low-pressure inductively coupled neon discharge“. Physics of Plasmas 29, Nr. 9 (September 2022): 093506. http://dx.doi.org/10.1063/5.0092091.
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A hysteresis phenomenon observed in neon inductive discharge at low gas pressure is investigated in terms of the evolution of the electron energy distribution function (EEDF). Generally, the hysteresis phenomenon has been reported at high-pressure Ramsauer gas discharges. However, in neon plasma, we found that the hysteresis phenomenon occurs even at low gas pressure (5 mTorr). Furthermore, the hysteresis vanishes with an increase in the gas pressure (10 and 25 mTorr). To analyze this hysteresis, the EEDF is measured depending on the radio frequency power. The EEDF at 10 mTorr sustains the bi-Maxwellian distribution during an E–H transition. On the other hand, the EEDF at 5 mTorr changes dramatically between discharge modes. At 5 mTorr, the measured EEDF for the E mode has the Maxwellian distribution due to high collisional heating in the bulk plasma. The EEDF for the H mode has the bi-Maxwellian distribution because collisionless heating in the skin depth is dominant. This apparent evolution of the EEDF causes a nonlinear energy loss due to collisions during the discharge mode transition. Therefore, the plasma can maintain the H mode discharge with high ionization efficiency, even at a lower applied power, which results in the hysteresis.
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Kaganovich, I. D., V. I. Demidov, S. F. Adams und Y. Raitses. „Non-local collisionless and collisional electron transport in low-temperature plasma“. Plasma Physics and Controlled Fusion 51, Nr. 12 (10.11.2009): 124003. http://dx.doi.org/10.1088/0741-3335/51/12/124003.
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Alharbi, A., I. Ballai, V. Fedun und G. Verth. „Waves in weakly ionized solar plasmas“. Monthly Notices of the Royal Astronomical Society 511, Nr. 4 (18.02.2022): 5274–86. http://dx.doi.org/10.1093/mnras/stac444.
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ABSTRACT Here, we study the nature and characteristics of waves propagating in partially ionized plasmas in the weakly ionized limit, typical for the lower part of the solar atmosphere. The framework in which the properties of waves are discussed depends on the relative magnitude of collisions between particles, but also on the relative magnitude of the collisional frequencies compared to the gyro-frequency of charged particles. Our investigation shows that the weakly ionized solar atmospheric plasma can be divided into two regions, and this division occurs, roughly, at the base of the chromosphere. In the solar photosphere, the plasma is non-magnetized and the dynamics can described within the three-fluid framework, where acoustic waves associated to each species can propagate. Due to the very high concentration of neutrals, the neutral sound waves propagates with no damping, while for the other two modes the damping rate is determined by collisions with neutrals. The ion- and electron-related acoustic modes propagate with a cut-off determined by the collisional frequency of these species with neutrals. In the weakly ionized chromosphere, only electrons are magnetized, however, the strong coupling of charged particles reduces the working framework to a two-fluid model. The disassociation of charged particles creates electric currents that can influence the characteristic of waves. The propagation properties of waves with respect to the angle of propagation are studied with the help of polar diagrams.
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Haggerty, Colby C., Antoine Bret und Damiano Caprioli. „Kinetic simulations of strongly magnetized parallel shocks: deviations from MHD jump conditions“. Monthly Notices of the Royal Astronomical Society 509, Nr. 2 (01.11.2021): 2084–90. http://dx.doi.org/10.1093/mnras/stab3110.
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ABSTRACT Shocks waves are a ubiquitous feature of many astrophysical plasma systems, and an important process for energy dissipation and transfer. The physics of these shock waves are frequently treated/modelled as a collisional, fluid magnetohydrodynamic (MHD) discontinuity, despite the fact that many shocks occur in the collisionless regime. In light of this, using fully kinetic, 3D simulations of non-relativistic, parallel propagating collisionless shocks comprised of electron-positron plasma, we detail the deviation of collisionless shocks form MHD predictions for varying magnetization/Alfvénic Mach numbers, with particular focus on systems with Alfénic Mach numbers much smaller than sonic Mach numbers. We show that the shock compression ratio decreases for sufficiently large upstream magnetic fields, in agreement with theoretical predictions from previous works. Additionally, we examine the role of magnetic field strength on the shock front width. This work reinforces a growing body of work that suggest that modelling many astrophysical systems with only a fluid plasma description omits potentially important physics.
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Akter, Shahrina, und M. G. Hafez. „Head-on collision between two-counter-propagating electron acoustic soliton and double layer in an unmagnetized plasma“. AIP Advances 13, Nr. 1 (01.01.2023): 015005. http://dx.doi.org/10.1063/5.0124133.
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The head-on collision between two-counter-propagating electron acoustic solitons and double layers (DLs) in an unmagnetized collisionless multi-species plasma consisting of inertial cold electron fluid and ( α, q)-distributed hot electrons and positrons has been analyzed with the stationary background of massive positive ions. For nonlinear analysis of colliding wave phenomena, the coupled Korteweg–de Vries equation (KdVE), modified KdVE (mKdVE), and standard Gardner equation have been derived by adopting the extended Poincaré–Lighthill–Kuo technique. The effect of non-dimensional parameters on the collisional KdV, mKdV, and Gardner solitons (GSs) and DLs has been examined in detail by considering the limiting cases of ( α, q)-distributions. It is found that the plasma model supports (i) the compressive and rarefactive collisional KdV solitons and GSs, (ii) only compressive mKdV solitons, and (iii) only rarefactive collisional DLs. The rarefactive collisional solitons are more affected by nonextensivity and the increase of the temperature of electrons than their compressive counterpart, whereas the rarefactive collisional DLs only existed in the presence of nonthermality.
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Alvarez Laguna, A., B. Esteves, A. Bourdon und P. Chabert. „A regularized high-order moment model to capture non-Maxwellian electron energy distribution function effects in partially ionized plasmas“. Physics of Plasmas 29, Nr. 8 (August 2022): 083507. http://dx.doi.org/10.1063/5.0095019.
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A model for electrons in partially ionized plasmas that self-consistently captures non-Maxwellian electron energy distribution function (EEDF) effects is presented. The model is based on the solution of scalar and vectorial velocity moments up to the contracted fourth-order moment. The set of fluid (macroscopic) equations is obtained with Grad's method and exact expressions for the collision production terms are derived, considering the electron–electron, electron–gas, and electron–ion elastic collisions as well as for electron–gas excitation and ionization collisions. A regularization of the equations is proposed in order to avoid spurious discontinuities, existing in the original Grad's moment model, by using a generalized Chapman–Enskog expansion that exploits the disparity of mass between the electrons and the heavy particles (ions and atoms) as well as the disparity of plasma and gas densities, typical of gas discharges. The transport model includes non-local effects due to spatial gradients in the EEDF as well as the impact of the EEDF in the calculation of the elastic and inelastic collision rates. Solutions of the moment model under spatially homogeneous conditions are compared to direct simulation Monte Carlo and a two-term Boltzmann solver under conditions that are representative of high plasma density discharges at low-pressure. The moment model is able to self-consistently capture the evolution of the EEDF, in good quantitative agreement with the kinetic solutions. The calculation of transport coefficients and collision rates of an argon plasma in thermal non-equilibrium under the effect of an electric field is in good agreement with the solutions of a two-term Boltzmann solver, largely improving models with a simplified Bhatnagar–Gross–Krook collisional operator.
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Øien, Alf H. „Kinetic and transport theory for a non-neutral plasma taking account of strong gyration and non-uniformities on the collisional scale“. Journal of Plasma Physics 38, Nr. 3 (Dezember 1987): 351–71. http://dx.doi.org/10.1017/s0022377800012654.
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From the BBGKY equations for a pure electron plasma a derivation is made of a collision integral that includes the combined effects of particle gyration in a strong magnetic field and non-uniformities of both the distribution function and the self-consistent electric field on the collisional scale. A series expansion of the collision integral through the distribution function and the electric field on the collisional scale is carried out to third order in derivatives of the distribution function and to second order in derivatives of the electric field. For the strong-magnetic-field case when collision-term contributions to only first order in 1/B are included, a particle flux transverse to the magnetic field proportional to l/B2 is derived. The importance of long-range collective collisions in this process is shown. The result is in contrast with the classical l/B4 proportionality, and is in accordance with earlier studies.
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Korn, J., und H. Schamel. „Electron holes and their role in the dynamics of current-carrying weakly collisional plasmas. Part 1. Immobile ions“. Journal of Plasma Physics 56, Nr. 2 (Oktober 1996): 307–37. http://dx.doi.org/10.1017/s0022377800019280.
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Solutions of the Vlasov-Fokker-Planck-Poisson system in a current-carrying plasma are analysed theoretically and numerically in the collisionless and weakly collisional approximations. The class of electron holes is extended, and new solitary electron hole and hump equilibria are found. Numerical solutions of the full time-dependent self-consistent problem are presented that show the non-existence of structural dissipative equilibria as long as ions are treated as an immobile background.
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McGowan, A. D., und J. J. Sanderson. „On the relaxation of non-thermal plasmas“. Journal of Plasma Physics 47, Nr. 3 (Juni 1992): 373–87. http://dx.doi.org/10.1017/s0022377800024296.
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The collisional relaxation of various plasma distributions that are initially far removed from thermal equilibrium is investigated numerically using a Fokker–Planck code. It is shown that self-similar and kappa distributions do not remain self-similar or kappa, and that this is due to the velocity dependence of the effective collision frequency. For the relaxation of an isotropic two temperature plasma it is shown that a constant-temperature three-component distribution function is a plausible model for analytical calculations. Investigation of the relaxation of bi-Maxwellian plasmas resolves some discrepancies that have arisen from earlier studies.
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Mašek, M., und K. Rohlena. „Kinetics of the Raman scattering in a laser corona using a transform method“. Laser and Particle Beams 35, Nr. 4 (06.11.2017): 687–98. http://dx.doi.org/10.1017/s0263034617000696.
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AbstractThis paper is an extension of our previous paper (Mašek and Rohlena, 2015), where we applied a transform method for the solution of Vlasov–Maxwell set of equations in a one-dimensional geometry to describe the Raman backscattering of the heating ns laser wave in the external corona of the generated laser plasma in a strongly non-linear regime. The method is stabilized by a simplified Fokker–Planck collision term, which, in turn, is used for a study of the influence of collisional and collisionless damping mechanisms of the daughter electron plasma wave (EPW) on the instability development and their competition resulting in a different instability behavior in various plasma configurations. The physics of trapped electrons is studied in detail and compared to the resulting Raman reflectivity. The Raman reflectivity was found to depend strongly on the intensity of laser irradiation in the different regions of the plasma corona. This is discussed in detail from the point of view of trapped electrons behavior in the EPW. Moreover, a study of the Raman reflectivity dependence on the electron–ion collision frequency (average plasma ionization) is presented, too. The results supplement the physical picture of the collision and collisionless processes influencing the Raman instability non-linear development.
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BALIKHIN, M., und M. GEDALIN. „Generalization of the Harris current sheet model for non-relativistic, relativistic and pair plasmas“. Journal of Plasma Physics 74, Nr. 6 (Dezember 2008): 749–63. http://dx.doi.org/10.1017/s002237780800723x.
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AbstractReconnection is believed to be responsible for plasma acceleration in a large number of space and astrophysical objects. Onset of reconnection is usually related to instabilities of current sheet equilibria. Analytical self-consistent models of an equilibrium current sheet (Harris equilibrium) are known for non-relativistic plasmas and some special cases of relativistic plasmas. We develop a description of generalized Harris equilibria in collisionless non-relativistic and relativistic plasmas. Possible shapes of the magnetic field are analyzed.
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Cremaschini, Claudio, John C. Miller und Massimo Tessarotto. „Kinetic closure conditions for quasi-stationary collisionless axisymmetric magnetoplasmas“. Proceedings of the International Astronomical Union 6, S274 (September 2010): 236–38. http://dx.doi.org/10.1017/s1743921311007010.
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AbstractA characteristic feature of fluid theories concerns the difficulty of uniquely defining consistent closure conditions for the fluid equations. In fact it is well known that fluid theories cannot generally provide a closed system of equations for the fluid fields. This feature is typical of collisionless plasmas where, in contrast to collisional plasmas, asymptotic closure conditions do not follow as a consequence of an H-theorem This issue is of particular relevance in astrophysics where fluid approaches are usually adopted. On the other hand, it is well known that the determination of the closure conditions is in principle achievable in the context of kinetic theory. In the case of multi-species thermal magnetoplasmas this requires the determination of the species tensor pressure and of the corresponding heat fluxes. In this paper we investigate this problem in the framework of the Vlasov-Maxwell description for collisionless axisymmetric magnetoplasmas arising in astrophysics, with particular reference to accretion discs around compact objects (like black holes and neutron stars). The dynamics of collisionless plasmas in these environments is determined by the simultaneous presence of gravitational and magnetic fields, where the latter may be both externally produced and self-generated by the plasma currents. Our starting point here is the construction of a solution for the stationary distribution function describing slowly-varying gyrokinetic equilibria. The treatment is applicable to non-relativistic axisymmetric systems characterized by temperature anisotropy and differential rotation flows. It is shown that the kinetic formalism allows one to solve the closure problem and to consistently compute the relevant fluid fields with the inclusion of finite Larmor-radius effects. The main features of the theory and relevant applications are discussed.
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Korn, J., und H. Schamel. „Electron holes and their role in the dynamics of current-carrying weakly collisional plasmas. Part 2. Mobile ions“. Journal of Plasma Physics 56, Nr. 2 (Oktober 1996): 339–59. http://dx.doi.org/10.1017/s0022377800019292.
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New dissipative structural equilibria of the Vlasov-Fokker-Planck-Poisson system in a current-carrying plasma with mobile ions are presented. The dynamical evolution towards these final equilibrium states is explored. First consequences for the parallel transport are derived and it is shown that the anomalous resistivity depends on non-symmetric distortions of the electron distribution function in the thermal range which are affected by collisions and ion mobility. The fundamental role of electron holes as the underlying collisionless structure is emphasized.
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Wang, L. P., Z. B. Guo, Z. J. Mao und Y. Zhang. „Phase finite time singularity: On the dissolution of a surface MHD eigenmode to the Alfvén continuum“. Physics of Plasmas 30, Nr. 3 (März 2023): 032105. http://dx.doi.org/10.1063/5.0132609.
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Phase mixing is a general mechanism of collisionless damping in magnetized plasmas. In a MHD model, the carrier of phase mixing is the Alfvén wave continuum, which is driven by the plasma inhomogeneity. In this work, we study the non-resonant conversion of a surface MHD eigenmode to the Alfvén continuum. It is shown that the finite-time-singularity of the phase of the surface mode can smear its periodic oscillation and induces the excitation of the local Alfvén waves. This type of mode conversion would enhance the collisionless dissipation of the surface eigenmode, i.e., accelerating its dissolution to the Alfvén continuum. The non-resonant mode conversion and damping mechanism explored here have potential applications to understand the physics of collisionless dissipation of various eigenmodes in magnetized plasmas.
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Prakash, Kirti, und Seema Manchanda. „Effects of Finite Larmor Radius and Hall Currents on Thermosolutal Instability of a Partially Ionized Plasma in Porous Medium“. Zeitschrift für Naturforschung A 49, Nr. 3 (01.03.1994): 469–74. http://dx.doi.org/10.1515/zna-1994-0304.
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Abstract The effects of finite ion Larmor radius (FLR), collisions and Hall currents on thermosolutal instability of a partially ionized plasma in porous medium in the presence of uniform vertical magnetic field are investigated. It is found that the presence of each magnetic field, FLR, Hall currents and collisions, introduces oscillatory modes which were, otherwise, non-existent. In the case of stationary convection, finite Larmor radius, Hall currents, medium permeability and magnetic field may have stabilizing or destabilizing effects, but for a certain wave number range, FLR, magnetic field and Hall currents have a complete stabilizing effect. The stable solute gradient always has stabilizing effect on the system whereas the collisional effects disappear for the case of stationary convection.
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BATISHCHEV, O. V., M. M. SHOUCRI, A. A. BATISHCHEVA und I. P. SHKAROFSKY. „Fully kinetic simulation of coupled plasma and neutral particles in scrape-off layer plasmas of fusion devices“. Journal of Plasma Physics 61, Nr. 2 (Februar 1999): 347–64. http://dx.doi.org/10.1017/s0022377898007375.
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Fluid descriptions of plasmas, which are usually applied to a collisional plasma, can only be justified for very small Coulomb Knudsen numbers. However, the scrape-off layer (SOL) plasmas of experimental magnetic confinement fusion devices tend to have operational regimes characterized by a Coulomb Knudsen number around 0.1. In interesting detached regimes of an SOL plasma in a tokamak, when the plasma detaches from the limiters or divertors, this number may increase along with the local plasma gradients. Plasma gradients are also known to increase (and thus drive non-local effects) in inertial confinement fusion. Neutrals, which are being produced owing to plasma recombination at the plasma–divertor interface, may be in a mixed collisional regime as well. Thus simultaneous kinetic treatments of plasma and neutral particles with self-consistent evaluation of boundary conditions at the material walls are required. We present a physical model and a numerical scheme, and discuss results of purely kinetic simulations of plasmas and neutrals for actual conditions in the Alcator C-Mod and Tokamak-de-Varennes experimental tokamaks. Results for both steady-state and transient regimes of SOL plasma flow are presented. Our approach, unlike particle-in-cell and Monte Carlo methods, is free from statistical noise.
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Øien, Alf H. „Kinetic equations for a non-uniform plasma in strong fields and resulting particle transport“. Journal of Plasma Physics 43, Nr. 2 (April 1990): 189–215. http://dx.doi.org/10.1017/s0022377800014744.
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From the BBGKY equations for a multi-component plasma a derivation of generalized kinetic equations valid for non-uniform, neutral as well as non-neutral plasmas in strong electric and magnetic fields is made. Explicit effects of particle gyration and non-uniformities on the collisional scale are included in the collision terms. For each particle species the collision terms describing interaction between the same or other particle species consist of two parts. The first part is a generalization of the corresponding classical term, to which it reduces when fields and non-uniformities are negligible on the collisional scales. The second part is non-vanishing when non-uniformities are taken account of on the collisional scale. For the case of a neutral plasma, particle transport transverse to the magnetic field and along the density gradient is found. The result shows an increase of particle transport as compared with the classical formula when the Larmor radii are smaller than the Debye length. The underlying mechanism for this increase is pointed out.
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Martinovic, M. M. „Orbit limited theory in the solar wind - κ distributions“. Serbian Astronomical Journal, Nr. 192 (2016): 27–34. http://dx.doi.org/10.2298/saj160220004m.
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When a solid object is immersed into ionized gas it gets brought to a certain value of electrostatic potential and surrounded by a space charge region called ?plasma sheath?. Through this region, particles are attracted or repelled from the surface of the charge collecting object. For collisionless plasma, this process is described by the so-called orbit limited theory, which explains how the collection of particles is determined by the collector geometry and plasma velocity distribution function (VDF). In this article, we provide explicit expressions for orbit-limited currents for generalized Lorentzian (?) distributions. This work is useful to describe the charging processes of objects in non-collisional plasmas like the solar wind, where the electrons VDF is often observed to exhibit quasi power-law populations of suprathermal particles. It is found that these ?suprathermals? considerably increase the charge collection. Since the surface charging process that determines the value of electrostatic potential is also affected by the plasma VDF, calculation of the collector potential in the solar wind is described along with some quantitative predictions. [Projekat Ministarstva nauke Republike Srbije, br. 176002] <br><br><font color="red"><b> This article has been corrected. Link to the correction <u><a href="http://dx.doi.org/10.2298/SAJ1795071E">10.2298/SAJ1795071E</a><u></b></font>
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Gordeev S.V., Ivanov V. A. und Skoblo Yu. E. „Dielectric barrier discharge in a low-pressure He-Ne mixture. Afterglow spectroscopy of 2p-=SUP=-5-=/SUP=-5s-> 2p-=SUP=-5-=/SUP=-3p transitions“. Optics and Spectroscopy 130, Nr. 5 (2022): 608. http://dx.doi.org/10.21883/eos.2022.05.54447.3208-21.
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The results of a spectroscopic study and simulation of the processes of population and destruction of the levels of the 2p55s configuration of a neon atom in a decaying plasma of a low-frequency barrier discharge in a He-Ne mixture are presented. Experimental conditions: helium pressure 0.08-22 Torr, neon pressure ≤ 3 mTorr, electron density less than 1011 cm-3. On the basis of data on the evolution of the populations of the 3si levels (in Paschen's notation) with a change in helium pressure, data on the rate constants of collisional processes that determine the kinetics of these levels in He-Ne plasma are obtained more accurate than those available in the literature. Keywords: dielectric barrier discharge, helium-neon plasma, excitation transfer, afterglow, inelastic collisions.
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Chee-Seng, Lim. „Switched-on evolution due to a temporal electron charge drifting subthermally through a warm collisional plasma“. Journal of Plasma Physics 33, Nr. 1 (Februar 1985): 83–106. http://dx.doi.org/10.1017/s0022377800002348.
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An electron charge is suddenly switched on while drifting through a warm collisional plasma. It acts thereafter with an arbitrary time-dependence. The evolution of the plasma, initially at rest, is considered in two and three dimensions. A general solution is first established for drift-modified slow plasma modes and then employed in subthermal drift analysis. Its abrupt switch-on causes the electron charge to release, during subthermal drift, a fully symmetric thermal front Г which subsequently expands ahead of it into an undisturbed receding expanse. A transversely symmetric response develops inside Г. On switch-off, the drifting charge releases another thermal front Г0 which also precedes it but trails non-concentrically behind Г. Plasma response continues after switch-off. Response properties between Г and Г0 differ strikingly from those inside Г0. Applications are next considered, first in three dimensions, for a subthermal pulsating electron with a generally complex frequency ω. The prepermanent state response inside Г comprises an axisymmetric dominant component ø∞ plus a spherically symmetric transient component øtr. ø∞ acquires the frequency ω. øtr has amplitudes dependent on and wave crests independent of both frequency ω and drift; it suffers a fast (slow) ω–independent temporal attenuation in a collisional (collisionless) plasma. The geometrical drift wave structure of ø∞ is closely examined for real ω and a collisionless plasma. Every energy surface associated with ø∞ nucleates at the electron; from there, it evolves slower than a phase surface, which eventually ‘disappears’ past Г. The leading energy surface, which nucleated at switch-on, develops permanently inside Г; it serves as an energy front that seals off the energy sustaining ø∞ since switch-on. Finally, the two-dimensional evolving drift field of an activated antenna line is computed.
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Zhu, Wanying, Ruilin Cui, Feng He, Tianliang Zhang und Jiting Ouyang. „On the mechanism of density peak at low magnetic field in argon helicon plasmas“. Physics of Plasmas 29, Nr. 9 (September 2022): 093511. http://dx.doi.org/10.1063/5.0091471.
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Helicon plasma density may show a non-monotonic dependence on the magnetic field at low strength, so-called “low-field peak (LFP).” We presented the multiple LFPs and the formation mechanism in argon helicon plasmas in this paper. Propagating conditions of helicon (H) and Trivelpiece–Gould (TG) waves in collisional plasmas were calculated based on the dispersion relation. It is demonstrated that there are two mechanisms during mode transition responsible for LFP, i.e., resonance of H- and TG-waves and anti-resonance of TG-wave. Especially, H-TG resonance of the highest axial mode in the helicon plasma results in a density jump rather than a density peak due to the mode transition from non-wave to co-H/TG-wave mode. Higher plasma density in lower magnetic fields is helpful for achievement of multiple LFPs in argon helicon plasmas.
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MENDONÇA, J. T., N. SHUKLA, D. P. RESENDES und A. SERBETO. „Ion acoustic waves in expanding strongly coupled plasmas“. Journal of Plasma Physics 79, Nr. 6 (30.07.2013): 1063–66. http://dx.doi.org/10.1017/s0022377813000810.
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AbstractWe consider the excitation and dispersion of ion acoustic waves in expanding ultracold plasmas, taking into account the influence of boundary conditions. A cylindrical plasma geometry is assumed. We show that temporal changes in the medium lead to a wave frequency shift, associated with an evolving radial and standing wave mode structure, and to the temporal change of the background plasma parameters. A non-collisional model for the cylindrical geometry is also proposed.
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Dhawan, Rajat, und Hitendra K. Malik. „Sheath formation mechanism in collisional electronegative warm plasma with two-temperature non-extensive distributed electrons and ionization“. Journal of Applied Physics 133, Nr. 4 (28.01.2023): 043303. http://dx.doi.org/10.1063/5.0120616.
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The sheath formation mechanism is modeled in a four-component collisional electronegative warm plasma considering the behavior of positive ions by fluid equations and of negative ions by the Boltzmann distribution, along with non-extensive distributions of hot and cold electrons. For a more realistic situation, the ion source term and the ionization rate are also included in the basic equations that are solved numerically by applying appropriate boundary conditions. A concept of sheath thickness measurement is established based on two approaches, namely, the zero-electron-density approach and the floating potential approach. An identical behavior of the sheath thickness is observed based on these approaches, which means that the floating potential approach confirms the efficacy of the zero-electron-density approach. Finally, the effects of various parameters such as the temperature of all the plasma species, collisions, ionization rate, and non-extensivity are evaluated on the profiles of the densities of plasma species, electric potential, and net space charge density for better understanding of the sheath formation mechanism. In comparison to electropositive plasma, a sharp fall in the potential for the case of electronegative plasma has been depicted, or in other words, higher potential gradient is realized in the electronegative plasma. Also, increasing negative ion temperature results in the reduced sheath thickness and produces a stronger gradient in the potential.
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Martínez-Gómez, D., B. Popescu Braileanu, E. Khomenko und P. Hunana. „Simulations of the Biermann battery mechanism in two-fluid partially ionised plasmas“. Astronomy & Astrophysics 650 (Juni 2021): A123. http://dx.doi.org/10.1051/0004-6361/202039113.
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Context. In the absence of an initial seed, the Biermann battery term of a non-ideal induction equation acts as a source that generates weak magnetic fields. These fields are then amplified via a dynamo mechanism. The Kelvin-Helmholtz instability is a fluid phenomenon that takes place in many astrophysical scenarios and can trigger the action of the Biermann battery and dynamo processes. Aims. We aim to investigate the effect of the ionisation degree of the plasma and the interaction between the charged and neutral species on the generation and amplification of magnetic fields during the different stages of the instability. Methods. We use the two-fluid model implemented in the numerical code Mancha-2F. We perform 2D simulations starting from a configuration with no initial magnetic field and which is unstable due to a velocity shear. We vary the ionisation degree of the plasma and we analyse the role that the different collisional terms included in the equations of the model play on the evolution of the instability and the generation of magnetic field. Results. We find that when no collisional coupling is considered between the two fluids, the effect of the Biermann battery mechanism does not depend on the ionisation degree. However, when elastic collisions are taken into account, the generation of magnetic field is increased as the ionisation degree is reduced. This behaviour is slightly enhanced if the process of charge-exchange is also considered. We also find a dependence on the total density of the plasma related to the dependence on the coupling degree between the two fluids. As the total density is increased, the results from the two-fluid model converge to the predictions of single-fluid models. Conclusions. The charged-neutral interaction in a partially ionised plasmas has a non-negligible effect on the Biermann battery mechanism and it effectively enhances the generation of a magnetic field. In addition, single-fluid models, which assume a very strong coupling between the two species, may overestimate the contribution of this interaction in comparison with two-fluid models.
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Leubner, M. P., und N. Schupfer. „A universal mirror wave-mode threshold condition for non-thermal space plasma environments“. Nonlinear Processes in Geophysics 9, Nr. 2 (30.04.2002): 75–78. http://dx.doi.org/10.5194/npg-9-75-2002.
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Abstract. Magnetic fluctuations are recognized in a large variety of space plasmas by increasingly high resolution, in situ observations as mirror wave mode structures. A typical requirement for the excitation of mirror modes is a dominant perpendicular pressure in a high-beta plasma environment. Contrary, we demonstrate from a realistic kinetic analysis how details of the velocity space distributions are of considerable significance for the instability threshold. Introducing the most common characteristics of observed ion and electron distributions by a mixed suprathermal-loss-cone, we derive a universal mirror instability criterion from an energy principle for collisionless plasmas. As a result, the transition from two temperature Maxwellians to realistic non-thermal features provides a strong source for the generation of mirror wave mode activity, reducing drastically the instability threshold. In particular, a number of space-related examples illuminate how the specific structure of the velocity space distribution dominates as a regulating excitation mechanism over the effects related to changes in the plasma parameters.
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Brickhouse, Nancy S., und Randall K. Smith. „Spectral Modeling with APEC“. Highlights of Astronomy 13 (2005): 651–52. http://dx.doi.org/10.1017/s1539299600016749.
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AbstractThe Astrophysical Plasma Emission Code (APEC) collaboration now provides public models for X-ray spectra of collisional equilibrium plasmas. These models facilitate the diagnosis of temperature, density, elemental abundance, charge state, and optical depth. We report benchmarking studies of the APEC models from the Emission Line Project, a project to test these models using high quality stellar coronal spectra. We discuss the implications of the benchmarked atomic data for non-equilibrium collisional models as well. Finally, we discuss the extension of APEC to other applications, such as opacity models for AGN.
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Singh, Arvinder, und Keshav Walia. „Self-focusing of laser beam in collisional plasma and its effect on Second Harmonic generation“. Laser and Particle Beams 29, Nr. 4 (04.10.2011): 407–14. http://dx.doi.org/10.1017/s0263034611000504.
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AbstractThis paper presents an investigation of self-focusing of Gaussian laser beam in collisional plasma and its effect on second harmonic generation. Due to non-uniform heating, collisional non-linearity arises, which leads to redistribution of carriers and hence affects the plasma wave, which in turn affects the second harmonic generation. Effect of the intensity of the laser beam/plasma density on the harmonic yield is studied in detail. We have set up the non-linear differential equations for the beam width parameters of the main beam, plasma wave, second harmonic generation and second harmonic yield by taking full non-linear part of the dielectric constant of collisional plasma with the help of moment theory approach. It is predicted from the analysis that harmonic yield increases/decreases due to increase in the plasma density/intensity of the laser beam respectively.
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HUMPHREY, K. A., R. M. G. M. TRINES, D. C. SPEIRS, P. NORREYS und R. BINGHAM. „The role of collisions on mode competition between the two-stream and Weibel instabilities“. Journal of Plasma Physics 79, Nr. 6 (Dezember 2013): 987–89. http://dx.doi.org/10.1017/s0022377813001177.
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AbstractWe present results from numerical simulations conducted to investigate a potential method for realizing the required fusion fuel heating in the fast ignition scheme to achieving inertial confinement fusion. A comparison will be made between collisionless and collisional particle-in-cell simulations of the relaxation of a non-thermal electron beam through the two-stream instability. The results presented demonstrate energy transfer to the plasma ion population from the laser-driven electron beam via the nonlinear wave–wave interaction associated with the two-stream instability. Evidence will also be provided for the effects of preferential damping of competing instabilities such as the Weibel mode found to be detrimental to the ion heating process.
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Bultel, Arnaud, Vincent Morel und Julien Annaloro. „Thermochemical Non-Equilibrium in Thermal Plasmas“. Atoms 7, Nr. 1 (01.01.2019): 5. http://dx.doi.org/10.3390/atoms7010005.
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In this paper, we analyze the departure from equilibrium in two specific types of thermal plasmas. The first type deals with the plasma produced during the atmospheric entry of a spatial vehicle in the upper layers of an atmosphere, specifically the one of Mars. The second type concerns the plasma produced during the laser-matter interaction above the breakdown threshold on a metallic sample. We successively describe the situation and give the way along which modeling tools are elaborated by avoiding any assumption on the thermochemical equilibrium. The key of the approach is to consider the excited states of the different species as independent species. Therefore, they obey to conservation equations involving collisional-radiative contributions related to the other excited states. These contributions are in part due to the influence of electrons and heavy particles having a different translation temperature. This ‘state-to-state’ approach then enables the verification of the excitation equilibrium by analyzing Boltzmann plots. This approach leads finally to a thorough analysis of the progressive coupling until the equilibrium asymptotically observed.
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LIU, SAN-QIU, und XIAO-CHANG CHEN. „Dispersion relation of transverse oscillation in relativistic plasmas with non-extensive distribution“. Journal of Plasma Physics 77, Nr. 5 (15.02.2011): 653–62. http://dx.doi.org/10.1017/s0022377811000043.
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AbstractThe generalized dispersion equation for superluminal transverse oscillation in an unmagnetized, collisionless, isotropic and relativistic plasma with non-extensive q-distribution is derived. The analytical dispersion relation is obtained in an ultra-relativistic regime, which is related to q-parameter and temperature. In the limit q → 1, the result based on the relativistic Maxwellian distribution is recovered. Using the numerical method, we obtain the full dispersion curve that cannot be given by an analytic method. It is shown that the numerical solution is in good agreement with the analytical result in the long-wavelength and short-wavelength region for ultra-relativistic plasmas.
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Tsunemi, H. „Non-Equilibrium Condition in the SNR“. Symposium - International Astronomical Union 188 (1998): 39–42. http://dx.doi.org/10.1017/s007418090011438x.
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SNe are one of the major source of the heavy elements in Galaxy. They produced high temperature plasma heavily contaminated with heavy elements mixing with the interstellar matter. Due to the temperature and the density, the shock heated plasma does not reach the collisional ionization condition in young SNR, like Cassiopeia A, Tycho and Kepler. The emission is well represented with a non-equilibrium condition plasma.
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Bachmann, P. K., G. Gärtner und H. Lydtin. „Plasma-Assisted Chemical Vapor Deposition Processes“. MRS Bulletin 13, Nr. 12 (Dezember 1988): 52–59. http://dx.doi.org/10.1557/s0883769400063703.
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Over the past two decades a vast number of publications have emerged from laboratories all over the world, describing the application of plasmas for preparing and processing materials. MRS symposia, scientific journals and books, and complete conference series are solely devoted to this specific topic.Modern VLSI integrated circuits, for instance, would simply not exist without sophisticated plasma etching techniques. But highly reactive, partly ionized and dissociated, quasi-neutral gases—plasmas—are not only useful for etching purposes, i.e., the removal of materials. They are also very valuable tools for the deposition of materials with unique structures and compositions at lower temperatures than for conventional thermally induced chemical vapor deposition processes. Backed by intensive research activities and more than a decade of practical experiences, plasma deposition technologies are now penetrating a number of industrial manufacturing processes.Plasmas can be classified into two basic categories — non-isothermal, and isothermal or thermal plasmas.Within the high electric fields applied for non-isothermal plasma generation at reduced pressure, free electrons are accelerated to energies that correspond to several thousand degrees in the case of thermal activation. The neutral species in the gas phase and the heavy ions are either not influenced by the fields or cannot follow changing fields fast enough. Their temperature stays low, resulting in a difference between electron and gas temperature. In these nonequilibrium plasmas, the collisions of high energy electrons and gas molecules result in dissociation processes that would only occur at very high temperatures of more than 5,000 K in the case of thermal equilibrium. Therefore, non-isothermal plasmas allow the preparation of materials and compositions that are difficult to obtain using thermally activated, conventional CVD. Due to the initiation of chemical reaction by collisions with “hot” electrons rather than hot gas molecules, the processing temperature can, in many cases, be kept lower than in conventional deposition processes.
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Dubin, Daniel H. E. „Collisional transport in non-neutral plasmas“. Physics of Plasmas 5, Nr. 5 (Mai 1998): 1688–94. http://dx.doi.org/10.1063/1.872837.
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van Ninhuijs, M. A. W., J. Beckers und O. J. Luiten. „Collisional microwave heating and wall interaction of an ultracold plasma in a resonant microwave cavity“. New Journal of Physics 24, Nr. 6 (01.06.2022): 063022. http://dx.doi.org/10.1088/1367-2630/ac6c46.
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Abstract Recently, we introduced a resonant microwave cavity as a diagnostic tool for the study of ultracold plasmas (UCPs). This diagnostic allows us to study the electron dynamics of UCPs non-destructively, very fast, and with high sensitivity by measuring the shift in the resonance frequency of a cavity, induced by a plasma. However, in an attempt to theoretically predict the frequency shift using a Gaussian self-similar expansion model, a three times faster plasma decay was observed in the experiment than found in the model. For this, we proposed two causes: plasma–wall interactions and collisional microwave heating. In this paper, we investigate the effect of both causes on the lifetime of the plasma. We present a simple analytical model to account for electrons being lost to the cavity walls. We find that the model agrees well with measurements performed on plasmas with different initial electron temperatures and that the earlier discrepancy can be attributed to electrons being lost to the walls. In addition, we perform measurements for different electric field strengths in the cavity and find that the electric field has a small, but noticeable effect on the lifetime of the plasma. By extending the model with the theory of collisional microwave heating, we find that this effect can be predicted quite well by treating the energy transferred from the microwave field to the plasma as additional initial excess energy for the electrons.
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Acosta-Tripailao, Belén, Denisse Pastén und Pablo S. Moya. „Applying the Horizontal Visibility Graph Method to Study Irreversibility of Electromagnetic Turbulence in Non-Thermal Plasmas“. Entropy 23, Nr. 4 (16.04.2021): 470. http://dx.doi.org/10.3390/e23040470.
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One of the fundamental open questions in plasma physics is the role of non-thermal particles distributions in poorly collisional plasma environments, a system that is commonly found throughout the Universe, e.g., the solar wind and the Earth’s magnetosphere correspond to natural plasma physics laboratories in which turbulent phenomena can be studied. Our study perspective is born from the method of Horizontal Visibility Graph (HVG) that has been developed in the last years to analyze time series avoiding the tedium and the high computational cost that other methods offer. Here, we build a complex network based on directed HVG technique applied to magnetic field fluctuations time series obtained from Particle In Cell (PIC) simulations of a magnetized collisionless plasma to distinguish the degree distributions and calculate the Kullback–Leibler Divergence (KLD) as a measure of relative entropy of data sets produced by processes that are not in equilibrium. First, we analyze the connectivity probability distribution for the undirected version of HVG finding how the Kappa distribution for low values of κ tends to be an uncorrelated time series, while the Maxwell–Boltzmann distribution shows a correlated stochastic processes behavior. Subsequently, we investigate the degree of temporary irreversibility of magnetic fluctuations that are self-generated by the plasma, comparing the case of a thermal plasma (described by a Maxwell–Botzmann velocity distribution function) with non-thermal Kappa distributions. We have shown that the KLD associated to the HVG is able to distinguish the level of reversibility that is associated to the thermal equilibrium in the plasma, because the dissipative degree of the system increases as the value of κ parameter decreases and the distribution function departs from the Maxwell–Boltzmann equilibrium.
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de Avillez, Miguel A., Gervásio J. Anela und Dieter Breitschwerdt. „Variability of the adiabatic parameter in monoatomic thermal and non-thermal plasmas“. Astronomy & Astrophysics 616 (August 2018): A58. http://dx.doi.org/10.1051/0004-6361/201832948.
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Context. Numerical models of the evolution of interstellar and integalactic plasmas often assume that the adiabatic parameter γ (the ratio of the specific heats) is constant (5/3 in monoatomic plasmas). However, γ is determined by the total internal energy of the plasma, which depends on the ionic and excitation state of the plasma. Hence, the adiabatic parameter may not be constant across the range of temperatures available in the interstellar medium. Aims. We aim to carry out detailed simulations of the thermal evolution of plasmas with Maxwell–Boltzmann and non-thermal (κ and n) electron distributions in order to determine the temperature variability of the total internal energy and of the adiabatic parameter. Methods. The plasma, composed of H, He, C, N, O, Ne, Mg, Si, S, and Fe atoms and ions, evolves under collisional ionization equilibrium conditions, from an initial temperature of 109 K. The calculations include electron impact ionization, radiative and dielectronic recombinations and line excitation. The ionization structure was calculated solving a system of 112 linear equations using the Gauss elimination method with scaled partial pivoting. Numerical integrations used in the calculation of ionization and excitation rates are carried out using the double-exponential over a semi-finite interval method. In both methods a precision of 10−15 is adopted. Results. The total internal energy of the plasma is mainly dominated by the ionization energy for temperatures lower than 8 × 104 K with the excitation energy having a contribution of less than one percent. In thermal and non-thermal plasmas composed of H, He, and metals, the adiabatic parameter evolution is determined by the H and He ionizations leading to a profile in general having three transitions. However, for κ distributed plasmas these three transitions are not observed for κ < 15 and for κ < 5 there are no transitions. In general, γ varies from 1.01 to 5/3. Lookup tables of the γ parameter are presented as supplementary material.
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Ivanov V. A. „Dissociative Recombination in the Afterglow of Low-pressure Barrier Discharge. Population of Ne(2p-=SUP=-5-=/SUP=-3d) Atoms“. Optics and Spectroscopy 130, Nr. 14 (2022): 2082. http://dx.doi.org/10.21883/eos.2022.14.53991.2177-21.
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The decaying neon plasma produced by the dielectric barrier discharge (DBD) in a cylindrical tube at a pressure of 0.1-40 Torr has been spectroscopically investigated to analyze the dissociative recombination (DR) of molecular ions with electrons as a mechanism for the formation of excited atoms. It is shown that, at the electron density in the afterglow less than 5·1010 cm-3 the DR is the dominant source of population of 3d levels at pressures PNe≥ 0.6 Torr. At lower pressures, the optical properties of the decaying plasma are formed to a greater extent by the collisional-radiative recombination of Ne+ ions. A significant variation of the relative intensities of the 3d->3p transition lines in the afterglow with a change in gas pressure was found, reflecting the effect of inelastic collisions on the formation of the spectrum of decaying plasma in the near infrared region. From measurements carried out at a pressure of 0.6 Torr, the relative values of the partial DR coefficients for the 3dj levels of the neon atom were found. Comparison of these data with measurements in the near ultraviolet region, containing the lines of 4p->3s transitions, indicates the need to take into account the cascade 4p->3d transitions to correctly solve the problem of the final products of dissociative recombination. Keywords: dielectric-barrier discharge, low-pressure plasma, optical emission spectroscopy, dissociative recombination, molecular ions, collisional-radiative recombination, cascade transitions.
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Carbone, Emile, Wouter Graef, Gerjan Hagelaar, Daan Boer, Matthew M. Hopkins, Jacob C. Stephens, Benjamin T. Yee, Sergey Pancheshnyi, Jan van Dijk und Leanne Pitchford. „Data Needs for Modeling Low-Temperature Non-Equilibrium Plasmas: The LXCat Project, History, Perspectives and a Tutorial“. Atoms 9, Nr. 1 (24.02.2021): 16. http://dx.doi.org/10.3390/atoms9010016.
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Technologies based on non-equilibrium, low-temperature plasmas are ubiquitous in today’s society. Plasma modeling plays an essential role in their understanding, development and optimization. An accurate description of electron and ion collisions with neutrals and their transport is required to correctly describe plasma properties as a function of external parameters. LXCat is an open-access, web-based platform for storing, exchanging and manipulating data needed for modeling the electron and ion components of non-equilibrium, low-temperature plasmas. The data types supported by LXCat are electron- and ion-scattering cross-sections with neutrals (total and differential), interaction potentials, oscillator strengths, and electron- and ion-swarm/transport parameters. Online tools allow users to identify and compare the data through plotting routines, and use the data to generate swarm parameters and reaction rates with the integrated electron Boltzmann solver. In this review, the historical evolution of the project and some perspectives on its future are discussed together with a tutorial review for using data from LXCat.
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Keenan, Brett D., Chrismond D. Smith, Daniel Livescu, Jeffrey Haack und Robert S. Pavel. „Simulation of a strong steady-state plasma shock in a warm dense matter regime“. Physics of Plasmas 30, Nr. 1 (Januar 2023): 012706. http://dx.doi.org/10.1063/5.0129941.
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The structure of collisional plasma shocks has been subject to an extensive, multi-decadal investigation—in the hydrodynamic, hybrid kinetic ion/electron fluid, and fully kinetic ion/electron limits. Despite this thoroughness, all of these studies apply exclusively to classical, weakly coupled plasmas. Here, we report the first results for a planar hydrodynamic simulation of a strong, steady-state shock in a subspace of the warm dense matter (WDM) regime. Specifically, we consider a plasma of fully degenerate electrons with moderate-to-strongly coupled ions. Since the WDM ion and electron transport coefficients and equation of state differ markedly from their non-degenerate, weak-coupling equivalents, we find that the structure of a WDM plasma shock notably deviates from the ideal plasma picture.
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JAMIL, M., CH UZMA, K. ZUBIA, I. ZEBA, H. M. RAFIQUE und M. SALIMULLAH. „Diamagnetic drift instabilities in collisional non-uniform quantum dusty magnetoplasmas“. Journal of Plasma Physics 78, Nr. 6 (17.04.2012): 589–93. http://dx.doi.org/10.1017/s0022377812000360.
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AbstractDust-acoustic and dust-lower-hybrid diamagnetic drift wave instabilities have been examined in a collisional non-uniform quantum dusty magnetoplasma. The dust-acoustic drift instability arises through the Fermi degenerate pressure of electrons for a high-density plasma, while for a relatively low-density collisional quantum plasma and short wavelength consideration, the instability is dominated by the Bohm potential effect exciting a new quantum dust-acoustic wave. In the long-range wavelength limit, dust-lower-hybrid waves are found to be unstable because of the diamagnetic drift of magnetized ions. Various possible instability conditions are found for diamagnetic drift instability.
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Cuperman, S., und D. Zoler. „An extended analytical solution of the Boltzmann equation for non-homogeneous fusion and astrophysical plasmas“. Journal of Plasma Physics 40, Nr. 3 (Dezember 1988): 441–53. http://dx.doi.org/10.1017/s0022377800013416.
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The perturbative Chapman-Enskog procedure for solving Boltzmann's equation, holding when f1 ≪ f0 (f = f0 + f1 + …), is replaced by a method that is free of such a limitation. This work represents an extension to the case of strongly anisotropic plasma systems and the spherical geometry of that of Campbell (1984, 1986). The solution obtained here is expressed in terms of prescribed ratios of mean free path for collisions, as well as electric and gravitational fields, to the temperature- and density-gradient lengths. This solution is also used to discuss the limitation of the conduction transport coefficients in electron plasmas.
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Nishikawa, T., H. Takabe und K. Mima. „Line profile modeling for non-LTE partially ionized plasmas based on average atom model with l–splitting“. Laser and Particle Beams 11, Nr. 1 (März 1993): 81–87. http://dx.doi.org/10.1017/s0263034600006935.
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We have developed a new opacity modeling of partially ionized high-Z plasma to solve radiation transport in fluid codes. The average atom model is used to describe the electronic state of the plasma. The electronic state of the plasma is determined by solving the collisional radiative equilibrium model. We have taken into account the electron energy level splitting owing to the difference in the azimuthal quantum number. To model the line groups made of the same electronic transitions from ions indifferent charge states, we used a statistical method and calculated the distribution of the charge states from the averaged electron population in each bound state. By using the new opacity model, we can well reproduce the X-ray spectra from the plasmas. It is found that the Δn = 0 transition can explain the peaked spectra near hv = 300 eV and l–splitted emission of the n = 5–4 transition can explain the flat spectra in the region of hv = 400–800 eV seen in the experiments.
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Attems, Maximilian, Yago Bea, Jorge Casalderrey-Solana, David Mateos, Daniel Santos-Oliván, Carlos F. Sopuerta, Miquel Triana und Miguel Zilhão. „Paths to equilibrium in non-conformal collisions“. EPJ Web of Conferences 175 (2018): 07030. http://dx.doi.org/10.1051/epjconf/201817507030.
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Ever since fast hydrodynamization has been observed in heavy ion collisions the understanding of the hot early out-of-equilibrium stage of such collisions has been a topic of intense research. We use the gauge/gravity duality to model the creation of a strongly coupled Quark-Gluon plasma in a non-conformal gauge theory. This numerical relativity study is the first non-conformal holographic simulation of a heavy ion collision and reveals the existence of new relaxation channels due to the presence of non-vanishing bulk viscosity. We study shock wave collisions at different energies in gauge theories with different degrees of non-conformality and compare three relaxation times which can occur in different orderings: the hydrodynamization time (when hydrodynamics becomes applicable), the EoSization time (when the average pressure approaches its equilibrium value) and the condensate relaxation time (when the expectation value of a scalar operator approaches its equilibrium value). We find that these processes can occur in several different orderings. In particular, the condensate can remain far from equilibrium even long after the plasma has hydrodynamized and EoSized.
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Shiratani, Masaharu, Masahiro Soejima, Hyun Woong Seo, Naho Itagaki und Kazunori Koga. „Fluctuation of Position and Energy of a Fine Particle in Plasma Nanofabrication“. Materials Science Forum 879 (November 2016): 1772–77. http://dx.doi.org/10.4028/www.scientific.net/msf.879.1772.
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We are developing plasma nanofabrication, namely, nanoand micro scale guided assembly using plasmas. We manipulate nanoand micro objects using electrostatic, electromagnetic, ion drag, neutral drag, and optical forces. The accuracy of positioning the objects depends on fluctuation of position and energy of a fine particle (= each object) in plasmas. Here we evaluate such fluctuations and discuss the mechanism behind them. In the first experiment, we grabbed a fine particle in plasma using an optical tweezers. The fine particle moves in a potential well made by the optical tweezers. This is a kind of Brownian motion and the position fluctuation can be caused by neutral molecule collisions, ion collisions, and fluctuation of electrostatic force. Among theses possible causes, fluctuation of electrostatic force may be main one. In the second experiment, we deduced interaction potential between two fine particles during their Coulomb collision. We found that there exist repulsive and attractive forces between them. The repulsive force is a screened Coulomb one, whereas the attractive force is likely a force due to a shadow effect, a non-collective attractive force. Moreover, we noted that there is a fluctuation of the potential, probably due to fluctuation of electrostatic force. These position and potential energy fluctuations may limit the accuracy of guided assembly using plasmas.