Post-solitons and electron vortices generated by femtosecond intense laser interacting with uniform near-critical-density plasmas

Generation of nonlinear structures, such as stimulated Raman side scattering waves, post-solitons and electron vortices, during ultra-short intense laser pulse transportation in near-critical-density (NCD) plasmas is studied by using multi-dimensional particle-in-cell (PIC) simulations. In two-dimensional geometries, both P- and S-polarized laser pulses are used to drive these nonlinear structures and to check the polarization effects on them. In the S-polarized case, the scattered waves can be captured by surrounding plasmas leading to the generation of post-solitons, while the main pulse excites convective electric currents leading to the formation of electron vortices through Kelvin-Helmholtz instability (KHI). In the P-polarized case, the scattered waves dissipate their energy by heating surrounding plasmas. Electron vortices are excited due to the hosing instability of the drive laser. These polarization dependent physical processes are reproduced in two different planes perpendicular to the laser propagation direction in three-dimensional simulation with linearly polarized laser driver. The current work provides inspiration for future experiments of laser-NCD plasma interactions.     

Filaments in high-speed counter-streaming plasma interactions driven by high-power laser pulses

Interactions of two counter-streaming plasmas driven by high power laser pulses are studied on Shenguang II laser facility.Filamentary structures were observed in the interaction region after the electrostatic shockwave decay.Theoretical analysis and observations indicate that the filaments are because of collisionless mechanisms,which are caused by the electromagnetic instability,such as the beam-Weibel instability.Collision experiments were also carried out for comparison and no filaments were generated.     

Ion-acoustic turbulence and anomalous transport

We present results for the dynamics of evolution of non-linear state plasmas in a d.c. electric field which causes ion-acoustic turbulence (IAT). We look at (1) the time variation of the drift electron velocity and of the effective collision frequency, (2) features of the redistribution and heating of resonance ions, (3) the evolution of the spectral and angular distribution of turbulent pulsations, (4) processes of heating of the bulk of the particles. The results of an analytical IAT theory are compared with computer simulations.Special attention is paid to the theory of inhomogeneous plasmas with IAT. A self-consistent theory of anomalous transport is presented. We discuss the anisotropy of anomalous transport and the influence of non-Maxwellian particle velocity distributions on the transport processes. The electromagnetic properties, self-organization and hydrodynamic instability of plasmas with IAT are discussed.     

Measurement of peeling mode edge current profile dynamics

Peeling modes, an instability mechanism underlying deleterious edge localized mode (ELM) activity in fusion-grade plasmas, are observed at the edge of limited plasmas in a low aspect ratio tokamak under conditions of high edge current density (J(edge) ～ 0.1 MA/m2) and low magnetic field (B ～ 0.1 T). They generate edge-localized, electromagnetic activity with low toroidal mode numbers n≤3 and amplitudes that scale strongly with measured J(edge)/B instability drive, consistent with theory. ELM-like field-aligned, current-carrying filaments form from an initial current-hole J(edge) perturbation that detach and propagate outward.     

Renormalized turbulence theory for the ion acoustic problem

Renormalized kinetic theory for the long range collective oscillations of turbulent plasmas is developed through infinite order summations of the interactions in the Vlasov-Poisson self-consistent field equations. Three levels of renormalized turbulence theory are derived, and the simply renormalized equations are solved for the problem of ion acoustic instability. The physical predictions of renormalized turbulence theory are discussed and used to interpret several experiments on ion acoustic turbulence.     

The role of self-consistency in double layer calculations

In a number of calculations involving nonlinear structures such as double layers and solitons, the Korteweg-de Vries theory is applied beyond its range of validity or approximations are made which are not self-consistent. Some situations arising in the theory of double layers in fluid multispecies plasmas are pointed out and attention is drawn to arbitrary-amplitude numerical calculations which yield results that are physically very different from those of the approximate theories. In particular, severe restrictions on the occurrence of ion-acoustic double layers in negative-ion plasmas and of electron-acoustic double layers in two-electron-component plasmas are found     

离子通道摇摆电子束流激发的纵向慢波不稳定性

考虑相对论电子束入射等离子体所产生的离子通道的具体结构,利用线性电磁流体力学理论对离子通道摇摆电子束激发的纵向慢波电磁不稳定性进行研究.通过对导出的系统色散关系的数值分析,给出了系统中电磁波、空间电荷波以及两者在一定条件下互作用形成的电磁-静电混合模式的传播特性.研究发现系统在慢波区域存在电磁不稳定性,并揭示此慢波不稳定性是由电子束的betatron振荡所导致,且系统的不稳定性程度与betatron振动频率密切相关.对betatron振荡激发的慢波电磁不稳定性物理机理进行了分析,并给出了不稳定性存在的条件 关键词： 离子通道 betatron振荡 电磁不稳定性     

Nonequilibrium MHD plasma flow in a high-interaction disk generator

Nonequilibrium MHD plasma flow in a high-interaction disk-type MHD generator is examined by numerical simulations based on the two-temperature model equations. The simulations are performed for the generators driven by working gases: He-Cs and He-K. Homogeneous and inhomogeneous plasma behavior is observed with change of the load resistance, and it is found that the structures of the inhomogeneous plasma differ for different seed materials. The plasma structures associated with both the partial ionization instability and the magnetoacoustic instability are discussed for both plasmas     

Electromagnetic instabilities in weakly relativistic plasmas

The spin-orbit coupling effects on the velocity space electromagnetic instabilities have been analytically studied. In this order, first, a suitable form of the kinetic theory is introduced and then, results are investigated for real ICF and astrophysical plasmas. For the ICF plasmas, Low intensity magnetic field can not provide a suitable field for effectiveness of the particle’s spin, while transmission to astrophysical subjects is different. For astrophysical applications, the spin-orbit coupling effects can lead to addition free energy so that, it can overcoming the non relativistic effects and leads to increasing the instability growth rate.     

Drift waves and counter rotating vortices in pair-ion plasmas

Linear dispersion relation has been found for drift and acoustic waves in pair-ion-electron plasmas. The stationary solution in the form of counter rotating vortices has been obtained in the presence of equilibrium potential profile. It is noticed that the speed of nonlinear structures is reduced with the increase of electrons concentration in pair-ion plasmas. Linear instability condition has also been found in the presence of shear flow. It is pointed out that the present results can be useful for future pair-ion plasma experiments.     

反常电子粘滞性引起的线性双撕裂模研究

用圆柱位形的磁流体动力学方程对由反常电子粘滞性引起的双撕裂模的线性行为做了数值研究.分析了两个有理面的间距、粘滞率大小和极向模数对双撕裂模模式结构的影响,给出了各种情况下双撕裂模线性增长率跟表征反常电子粘滞率大小的电子雷诺数的定标关系.     

Opacity calculations for Non-Local-Thermodynamic-Equilibrium plasmas

In this paper, we presented a method to calculate the spectral-resolved opacity for Non-Local-Thermodynamic-Equilibrium (non-LTE) plasmas. By solving the rate equations, we get the population. In the rate equations, configuration-averaged rate coefficients are used and the cross sections are calculated based on the first-perturbation theory. Using the detailed configuration accounting with the term structures treated by the unresolved transition array model, we calculated the spectral-resolved opacity of Al plasmas. The results are compared with those of other theoretical models. From the comparison, we can see that the present results fit well with other models for low-Z plasmas. For high-Z plasmas, we will give detailed discussion in the future.     

On the current-driven electrostatic ion-cyclotron instability: areview

Theoretical, numerical, and experimental investigations of the electrostatic ion-cyclotron instability (EICI) are critically reviewed. The discussion of theory focuses mainly on the linear theories, with particular attention to those that have been used in explaining experimental observations, but a short account of various nonlinear theories is also given. Numerical simulation results are surveyed. Experimental investigations in Q-machine plasmas and their interpretation in terms of various theories are then examined     

Oscillatory Turing patterns in reaction-diffusion systems with two coupled layers

A model reaction-diffusion system with two coupled layers yields oscillatory Turing patterns when oscillation occurs in one layer and the other supports stationary Turing structures. Patterns include "twinkling eyes," where oscillating Turing spots are arranged as a hexagonal lattice, and localized spiral or concentric waves within spot-like or stripe-like Turing structures. A new approach to generating the short-wave instability is proposed.     

Nonlinear Theory of the Instability of a Modulated Electron Beam of Low Density in a Plasma. V. Excitation of Waves in Strong Dissipative Plasmas by a Monoenergetic Beam

A system of nonlinear equations derived in a previous paper which describes the evolution of the beam-plasma instability in strong dissipative plasmas is solved numerically. It is shown that there are three characteristic solutions of the system of equations: the resonant dissipative instability, the nonresonant instability with strong dissipation and the nonresonant dissipative instability. A physical interpretation of essential features of these instabilities is given. The interaction of resonant and nonresonant waves in the system electron beam-strong dissipative plasma is examined. Some conclusions for the transport problem of electron beams in strong dissipative plasmas are obtained in this paper.     

Convective instability of the thermovibrational flow of binary mixture in the presence of the Soret effect

The convective instability of the thermovibration flow in a plane horizontal layer filled with an incompressible binary gaseous mixture is investigated. The study takes into account the effect of thermal diffusion or the Ludwig-Soret effect. Several instability mechanisms are discussed. To determine the instability threshold with respect to cell and long-wave perturbations, the Floquet theory was applied to the linearized equations of convection formulated in the Boussinesq approximation. We found that regime parametric instability can occur owing to the finite frequency vibrations. The evolution of plane, spiral and three-dimensional disturbances is studied. We demonstrated that, because of the properties of the system, the subharmonic response of plane disturbances to the external periodic action cannot be observed. The instability can be associated only with synchronous or quasiperiodic modes. Depending on the vibration parameters, modulations can stabilize or destabilize the base state. For spiral perturbations the stability boundary does not depend on the amplitude and frequency of vibrations. In the case of long-wave instability we apply the regular perturbation approach with the wavenumber as a small parameter in power expansions. The stability boundaries are found.     

Modulational instability of ultra-intense linearly polarized laser pulse in electron–positron plasmas

Based on the wave equation of ultra-intense linearly polarized laser pulse propagating in electron–positron plasmas, the modulational instability is investigated. The nonlinear dispersion relation and the growth rate of instability are derived. The effects of plasmas number density, temperature, and laser intensity on the growth rate are analyzed. Results show that in an electron–positron plasma with certain background density, the intensity of the modulation instability is mainly determined by the competition between the nonlinearity in the interaction and the relativistic light ponderomotive driven density responses.     

Experiments on plasma-physical aspects of closed cycle MHD power generation

In this paper, important laboratory experiments in closed-cycle magneto-hydrodynamic (MHD) generator plasmas are discussed. The following aspects are treated: electron temperature elevation and nonequilibrium ionization, fluctuations and nonuniformity, streamers as the nonlinear appearance of ionization instability, inlet relaxation, and fully ionized seed as a concept to suppress ionization instability. Conclusions are presented on electrical transport parameters in nonuniform plasmas, streamer fine structure, streamer velocity, streamer initiation in relation to inlet relaxation, and the fully ionized seed concept.