The nonlinear propagation of electromagnetic waves in pair plasmas, in which the electrostatic potential plays a very important but subdominant role of a "binding glue" is investigated. Several mechanisms for structure formation are investigated, in particular, the "asymmetry" in the initial temperatures of the constituent species. It is shown that the temperature asymmetry leads to a (localizing) nonlinearity that is new and qualitatively different from the ones originating in ambient mass or density difference. The temperature asymmetry driven focusing-defocusing nonlinearity supports stable localized wave structures in 1-3 dimensions, which, for certain parameters, may have flat-top shapes.
The effect of the Coriolis force due to the impurity toroidal and poloidal rotation on the in-out impurity density asymmetry in a rotating tokamak plasma is identified. The in-out impurity density asymmetry can be induced by the Coriolis force with q*v_theta_z*omega_z, in this case, when moving along the magnetic field line from the outboard side to the inboard side in a magnetic flux surface, one sees a positive Coriolis force. The proposed theory is consistent with the ASDEX Upgrade experimental observations.
Using particle-in-cell simulation technique, we investigate the plasma and ionization asymmetry, electron and ion energy distribution function in capacitive discharges excited by tailored waveforms. At a base frequency of 13.56 MHz, three different waveforms namely, sinusoidal, saw-tooth, and square are applied for a constant current density of 50 A/m2 and 5 mTorr argon gas pressure. The simulation results show that the square waveform produces the highest plasma density in the discharge, whereas maximum asymmetry is observed for plasma excited by sawtooth like waveform. Both square and sawtoo…
Direct asymmetry measurement of temperature and density spatial distributions in inertial confinement fusion plasmas from pinhole space-resolved spectra
In this manuscript, a fluid model is utilized to calculate the density of plasma species assuming geometrically symmetric Ar/CF4 Radiofrequency Capacitively Coupled Plasmas. The electrodes are driven by a sinusoidal waefront with an amplitude of 200 V and a frequency of 13.56 MHz. The gap between the electrodes is 5cm. The plasma species density is calculated as a function of the gas pressure, electron temperature, and the gas composition. In a good agreement with recent experimental results, $CF^+_3$ and F are dominant for all considered simulation parameters. The results explain the pathways…
The spontaneous evolution of magnetic reconnection in generalized situations (with thermodynamic asymmetry regarding the current sheet and magnetic shear) is investigated using two-dimensional magnetohydrodynamic simulation. We focus on the asymptotic state of temporal evolution, i.e., the self-similarly expanding phase (Nitta et al. 2001). 1) A long fast-mode shock is generated in front of the shorter plasmoid as in the shear-less thermodynamically asymmetric case; however, the sheared magnetic component weakens the shock. This fast shock may work as a particle acceleration site. 2) The short…
A magnetosphere comparable in size to ion inertial length, known as a mini-magnetosphere, possesses unusual features which have been predicted by numerical simulations and shown in recent experiments. In the present paper we study a pronounced difference between the west and east flanks of a mini-magnetosphere observed for the first time in pioneering terrella experiments of 60 s duration. It manifests itself in plasma penetration deep inside the west flank and the formation of a return current that effects the magnetic structure, in contrast to the east flank which has a well-defined boundary…
Applications of dielectric barrier discharge (DBD) based atmospheric pressure plasma jets are often limited by the relatively small area of treatment due to their 1D configuration. This letter describes the first results demonstrating generation of 2D plasma bullets and 2D plasma jets permitting fast treatment of large targets. Imaging of pulsed DBD in He and ionization wave propagation along the dielectric surface show that DBD evolution starts with formation of transient anode glow, and only then continues with development of cathode-directed streamers. The anode glow can propagate as an ion…
Compton scattering of gamma rays propagating in a pair plasma can drive the formation of a relativistic electron positron beam. This process is scrutinised theoretically and numerically via particle-in-cell simulations. In addition, we determine in which conditions the beam can prompt a beam-plasma instability and convert its kinetic energy into magnetic energy. We argue that such conditions can be met at the photosphere radius of bright Gamma Ray Bursts.
The formation of the plasma current spike at the end of the thermal quench phase is studied systematically, which is found to strongly correlate to the onset of the 1/1 kink-tearing reconnection in the simulation results. The magnetohydrodynamic (MHD) activity on the q = 1 surface plays a critical role in the spike formation and the disruption process, namely, when the safety factor in the magnetic axis q0 exceeds 1, the plasma major disruption transits into successive minor disruptions and the start of thermal quench phase is delayed.
We present experimental data providing evidence for the formation of transient ($\sim 20~μ$s) plasmas that are simultaneously weakly magnetized (i.e., Hall magnetization parameter $ωτ> 1$) and dominated by thermal pressure (i.e., ratio of thermal-to-magnetic pressure $β> 1$). Particle collisional mean free paths are an appreciable fraction of the overall system size. These plasmas are formed via the head-on merging of two plasmas launched by magnetized coaxial guns. The ratio $λ_{gun}=μ_0 I_{gun}/ψ_{gun}$ of gun current $I_{gun}$ to applied magnetic flux $ψ_{gun}$ is an experimental knob for e…
Collisionless Larmor Coupling and Blob Formation in a Laser-Plasma Expanding into a Magnetized Ambient Plasma
University of California–Los Angeles（加州大学洛杉矶分校）；Laboratoire d’Optique Appliquée (LOA), CNRS, École polytechnique, ENSTA, Institut Polytechnique de Paris（应用光学实验室，法国国家科学研究中心，巴黎综合理工学院，ENSTA，巴黎理工学院）；Lawrence Livermore National Laboratory（劳伦斯利弗莫尔国家实验室）；Los Alamos National Laboratory（洛斯阿拉莫斯国家实验室）
A review of the theoretical and computational aspects of plasma-wall transition is presented. The conditions for the existence of plasma sheaths in front of a solid surface are established. Various regimes are analyzed -collisionless and collisional. fluid and kinetic, with and without ionization. The partition of the plasma-wall transition into distinct regions (Debye sheath, quasineutral presheath. magnetic presheath, etc...) is also discussed. Applications to the theory of electrostatic probes are illustrated by means of a recently developed kinetic model. The influence of the probe on ion …
In this paper, we consider ionospheric plasma consisting of weakly degenerate electrons and heavy ions. We embrace our hydrodynamic model by including the quantum diffraction term. By employing Sagdeev's pseudo-potential method, we obtain double layers and soliton structure. We have studied the various parametric dependence of solitary structures and double layers. The results thus obtained might be helpful in the studies of many high energy astrophysical phenomena.
We investigate the formation of collisionless magnetized shocks triggered by the interaction between magnetized plasma flows and miniature-sized (order of plasma kinetic-scales) magnetic obstacles resorting to massively parallel, full particle-in-cell simulations, including the electron kinetics. The critical obstacle size to generate a compressed plasma region ahead of these objects is determined by independently varying the magnitude of the dipolar magnetic moment and the plasma magnetization. We find that the effective size of the obstacle depends on the relative orientation between the dip…
Investigation of Vortex Structures in Gas-Discharge Nonneutral Electron Plasma: III. Pulse Ejection of Electrons at the Formation and Radial Oscillations of Vortex Structure
A new type of nonlinear dust pulse structures has been observed in afterglow complex plasma under microgravity condition on board the International Space Station (ISS). The dust pulses are triggered spontaneously as the plasma is switched off and the particles start to flow through each other (uni-directional or counter-streaming) in the presence of a low-frequency external electric excitation. The pulses are oblique with respect to the microparticle cloud and appear to be symmetric with respect to the central axis. A possible explanation of this observation with the spontaneous development of…
Every second millions of small meteoroids enter the Earth's atmosphere producing dense plasmas. Radars easily detect these plasmas and researchers use this data to characterize both the meteoroids and the atmosphere. This paper develops a first-principle kinetic theory describing the behavior of particles, ablated from a fast-moving meteoroid, that colliside with the atmospheric molecules. This theory produces analytic expressions describing the spatial structure and velocity distributions of ions and neutrals near the ablating meteoroid. This analytical model will serve as a basis for a more …
This paper calculates the spatial distribution of the plasma responsible for radar head echoes by applying the kinetic theory developed in the companion paper (Dimant and Oppenheim, arXiv:1608.08524). This results in a set of analytic expressions for the plasma density as a function of distance from the meteoroid. It shows that, at distances less than a collisional mean-free-path from the meteoroid surface, the plasma density drops in proportion to $1/R$ where $R$ is the distance from the meteoroid center; and, at distances much longer than the mean-free-path behind the meteoroid, the density …
The emergence of a density bump at the front of a collisionless electrostatic shock wave have been observed experimentally during the ablation of an aluminium foil by a femtosecond laser pulse. We have performed numerical simulations of the dynamics of this phenomena developing alongside the generation of a package of ion-acoustic waves, exposed to a continual flow of energetic electrons, in a collisionless plasma. We present the physical interpretation of the observed effects and show that the bump consists of transit particles, namely, the accelerated ions from the dense plasma layer, and th…
Recent observations of the successive formations of the 4=1; 3=1, and 2=1 magnetic islands as well as the subsequent braking of the 2=1 mode during a low-Z impurity penetration process in EAST experiments are well reproduced in our 3D resistive MHD simulations. The enhanced parallel current perturbation induced by impurity radiation predominately contributes to the tearing mode growth, and the 2=1 island rotation is mainly damped by the impurity accumulation as results of the influence from high n modes.
We present the first observations of a square lattice formation in a monodisperse complex plasma system - a configurational transition phenomenon that has long been an experimental challenge in the field. The experiments are conducted in a tabletop L-shaped Dusty Plasma Experimental (DPEx-II) device in a DC glow discharge Argon plasma environment. By a careful control of the vertical potential confining the charged particles as well as the strength of the ion wake charge interactions with the dust particles we are able to steer the system towards a crystalline phase that exhibits a square latt…
Positive and negative ions forming so-called pair plasma differing in sign of their charge and asymmetric in mass and temperature support a new electrostatic mode. Bernstein mode for a pair ions and pair ions with contribution of electrons in pair plasma both cases are investigated. By solving the linearized Vlasov equation along Maxwell equations, a generalized expression for the Bernstein waves is derived by employing the Maxwell distribution function. In paper we discuss the different types of ions Bernstein waves and comparison of the symmetry and asymmetry on these ions Bernstein waves. W…
It is well known that when a short laser pulse propagates in an underdense plasma, it induces longitudinal plasma oscillations at the plasma frequency after the pulse, typically referred to as the 'wakefield'. However, for plasma densities approaching the critical density wakefield generation is suppressed, and instead the EM-pulse undergoes nonlinear self-modulation. In this article we have studied the transition from the wakefield generation to formation of quasi-solitons as the plasma density is increased. For this purpose we have applied a one dimensional (1D) relativistic cold fluid model…
A model of a stable plasma formation, based on radial quantum oscillations of charged particles, is discussed. The given plasmoid is described with the help of the nonlinear Schrödinger equation. A new phenomenon of the effective attraction between oscillating charged particles is considered within the framework of the proposed model. The possible existence of a composite plasma structure is also discussed. Hypothesis about using the obtained results to describe natural long-lived plasma formations, which can serve as alternative energy sources, is put forward.
The ultra low frequency modes associated to the activated dust specie in a bounded cylinder orientation plasma has been investigated here. Here flow of all plasma particles is assumed along the axial coordinates where gradients in velocity are set to be along radial direction. This analysis has been carried out for both Maxwellian and non-Maxwellian (Kappa and Carins) dusty plasma where coupling of electrostatic dust acoustic and drift modes drives global vortex formations. The coefficients of the vortex solution has been affected strongly by the presence of superthermal particles. Significanc…
The additional pumping of energy into arc plasma flow by the self-consistently formed radially directed beam of high-energy electrons for evaporation of micro-droplets is considered. The radial beam appears near the inner cylindrical surface by secondary ion - electron emission at this surface bombardment by peripheral arc plasma flow ions. The beam is accelerated by electric potential jump, appeared in a cylindrical channel of the plasma-optical system in crossed radial electrical and longitudinal magnetic fields. The high-energy electrons pump, during the time of micro-droplet movement throu…
There is a new effect that can limit the lifetime of a weakly nonlinear wakefield in a radially bounded plasma. If the drive beam is narrow, some of the plasma electrons fall out of the collective motion and leave the plasma radially, forming a negatively charged halo around it. These electrons repeatedly return to the plasma under the action of the charge separation field, interact with the plasma wave and cause its damping. The lowest-energy halo electrons take the energy from the wave more efficiently, because their trajectories are bent by the plasma wave towards the regions of the stronge…
