Collisional relaxation of superthermal electrons generated by relativistic laser pulses in dense plasma

Energy relaxation of the hot electron population generated by relativistic laser pulses in overdense plasma is analyzed for densities ranging from below to 1000 times solid density. It is predicted that longitudinal beam-plasma instabilities, which dominate energy transfer between hot electrons and plasma at lower densities, are suppressed by collisions beyond solid density. The respective roles of collisional energy transfer modes, i.e., direct collisions, diffusion, and resistive return current heating, are identified with respect to plasma density. The transition between the kinetic and the collisional regimes and scalings of collisional process are demonstrated by a fully integrated one-dimensional collisional particle simulation.     

Plasma heating by a modulated relativistic electron beam-plasma interaction

We study experimentally the interaction of a current-modulated relativistic electron beam with a mirror-confined plasma. A high-power transmitter (500 MHz, 1 GW) is developed. Rapid heating takes place up to ≈ 900 eV, which is interpreted as a lower-hybrid parametric instability.     

Relativistic electron beams and beam-plasma interaction

The interaction of a (relativistic) electron beam with a plasma is discussed. In the introduction the history of the field and related topics are reviewed. Next the momentum space distribution of a relativistic electron beam (REB) is treated. Then, taking into account the kinetic properties of a REB, linear wave dispersion in a REB-plasma system is surveyed. Dispersion diagrams are calculated and presented for a number of representative sets of parameters. Finally a discussion is given of the dispersive properties of unstable waves. Criteria are developed to discriminate between the various types of possible non-linear behaviour of the waves as they grow to their saturation level.     

A simple model of non-linear beam-plasma interaction

A microscopic Lagrangian and Hamiltonian is derived for the waves on a beam-plasma system with the reaction of the waves on the background self-consistently taken into account. Numerical integration of the corresponding canonical equations confirms that even a model of only several degrees of freedom suffices to describe the basic non-linear phenomena of beam-plasma interaction.     

Shock waves in magnetized plasmas with superthermal trapped electrons.

Formation of ion-acoustic shock waves (IAShWs) and their propagation nature in a magnetized plasma in the presence of superthermal trapped electrons are investigated for the first time via the fluid dynamical approach. A magnetized plasma system, comprising of inertial ions and non-inertial electrons following $\kappa$-superthermal trapped distribution, is considered to examine the basic features (amplitude, width, phase speed, etc.) of IAShWs in such a plasma. A diffusion effect (due to the ion kinematic viscosity) is taken into account. The reductive perturbation technique is adopted to derive the modified Korteweg de-Vries Burgers’ (mKdVB) equation and the solution of mKdVB equation (derived by adopting the tangent hyperbolic method) is used to investigate the dynamical and structural characteristics (speed, amplitude, width, etc.) of IAShWs. The influence of relevant plasma (configuration) parameters (e.g., the superthermality index $\kappa ,$ concentration of trapped electrons, external magnetic field, and obliquity angle, etc.) on the nature of IAShWs is examined. The applications of the results in space and laboratory plasma environments, where nonthermal trapped electrons are available, are briefly discussed.     

Effect of superthermal electrons on dust-acoustic Gardner solitons in nonplanar geometry

The properties of nonplanar (cylindrical and spherical) dust-acoustic solitary waves (DASWs) in an unmagnetized, collisionless three-component dusty plasma, whose constituents are negatively charged cold dust fluid, superthermal/non-Maxwellian electrons (represented by kappa distribution) and Boltzmann distributed ions, are investigated by deriving the modified Gardner (MG) equation. The well-known reductive perturbation method is employed to derive the MG equation. The basic features of nonplanar DA Gardner solitons (GSs) are discussed. It is seen that the properties of nonplanar DAGSs (positive and negative) significantly differ as the value of spectral index κ changes.     

Self-consistent modelling of plasma-solid interaction

In the paper the transport of electrons and ions in plasma is studied by computer simulation. The main goal of the modelling was to establish an exact form of energy distributions of charged particles near the metal substrates immersed into plasma and to analyse changes in their distributions during the transport through both the presheath and the sheath for various voltage biases and substrate geometries. Further results concern the probe characteristics both in inert gas and chemically active plasma and the distribution of potential and space charge in the vicinity of metal electrodes. As a simulation technique the combination of molecular dynamics and Monte Carlo methods was used. The movement of charged particles in self-consistent electric field was studied under the assumption of internal symmetry of the problem, which enabled to reduce the number of necessary coordinates to four (either 1d3v or 2d2v).     

Optical phonon generation by photoexcited electrons

Optical-phonon generation rate of photoexcited electrons via polarization and deformation electron-phonon interaction is calculated. The electron distribution function at energies higher than the optical-phonon energy is found.     

Electron-scale electrostatic solitary waves and shocks: the role of superthermal electrons

The propagation of electron-acoustic solitary waves and shock structures is investigated in a plasma characterized by a superthermal electron population. A three-component plasma model configuration is employed, consisting of inertial (“cold”) electrons, inertialess κ (kappa) distributed superthermal (“hot”) electrons and stationary ions. A multiscale method is employed, leading to a Korteweg-de Vries (KdV) equation for the electrostatic potential (in the absence of dissipation). Taking into account dissipation, a hybrid Korteweg-de Vries-Burgers (KdVB) equation is derived. Exact negative-potential pulse- and kink-shaped solutions (shocks) are obtained. The relative strength among dispersion, nonlinearity and damping coefficients is discussed. Excitations formed in superthermal plasma (finite κ) are narrower and steeper, compared to the Maxwellian case (infinite κ). A series of numerical simulations confirms that energy initially stored in a solitary pulse which propagates in a stable manner for large κ (Maxwellian plasma) may break down to smaller structures or/and to random oscillations, when it encounters a small-κ (nonthermal) region. On the other hand, shock structures used as initial conditions for numerical simulations were shown to be robust, essentially responding to changed in the environment by a simple profile change (in width).     

HL-1M装置电子回旋加热过程中的超热电子测量

在HL-1M托卡马克上进行的电子圆旋共振加热实验表明,在低等离子体密度加热过程中。产生大量的超热电子。由Si(Li)和碘化汞(HgI2)半导体探测器阵列测量到的软X射线和中能(15～150keV)X射线能谱,得到超热电子的温度在30～60keV范围内。中能X射线辐射强度测量结果证实,等离子体对电子圆麓波的吸收是定域性的。在超热电子对MHD的相互作用中,主要的m／n=2/1模没有增强或抑制现象。     

Nonlinear theory of resonant beam-plasma interaction: Nonrelativistic case

Analytic and numerical methods are used to study the nonlinear dynamics of the resonant interaction between a dense nonrelativistic electron beam and a plasma in a spatially bounded system. Regimes such as collective (Raman) and single-particle (Thomson) Cherenkov effects are considered. It is shown that in the first case, the motion of both the beam and plasma electrons exhibits significant nonlinearities. However, because of the weak coupling between the beam and the plasma, the nonlinear dynamics of the instability can be studied analytically and it can be strictly shown that saturation of instability is caused by a nonlinear shift of the radiation frequency and loss of resonance. In the second case, the nonlinear instability dynamics can only be studied numerically. In this regime, at low beam densities significant nonlinearity is only observed in the motion of the beam electrons while the plasma remains linear and saturation of the instability is caused by trapping of beam electrons in the field of the beam-excited plasma wave.     

Self-consistent current motion of electrons and ions inhigh-current plasma channel

This paper analyses a self-consistent current motion of charged particles in high-current plasma channel. Application of the results obtained to real current channels is possible provided that pair collisions do not considerably affect the current motion of plasma charged particles and the depth of the current layer is small as compared to the channel radius. The approximation adopted in this paper can be considered to be true, for instance, in the case of hydrogen channels with millimeter radius and electron energy of the order of 10 keV provided that the plasma concentration in them is in the range of 10 ¹⁷ cm^-3e<10²⁰ cm^-3. In the present paper, advantage is taken of a kinetic plasma model with electrons and ions in the form of particle beams whose motion is governed by the resulting self-consistent electromagnetic field. It is shown that in a plasma with sufficiently high particle concentration, when the collisionless skin depth is small as compared to the channel radius, the ion motion results in the negative electron contribution to the total channel current. Moreover, the ion component of the current exceeds the total current. This is accompanied by high-speed plasma motion in the form of the electroneutral axial flux, whose direction coincides with that of the total channel current     

Effects of bi-kappa distributed electrons on dust-ion-acoustic shock waves in dusty superthermal plasmas

The basic properties of dust-ion-acoustic （DIA） shock waves in an unmagnetized dusty plasma （containing inertial ions, kappa distributed electrons with two distinct temperatures, and negatively charged immobile dust grains） are investi- gated both numerically and analytically. The hydrodynamic equation for inertial ions has been used to derive the Burgers equation. The effects of superthermal bi-kappa electrons and ion kinematic viscosity, which are found to modify the basic features of DIA shock waves significantly, are briefly discussed.     

Third harmonic generation by hot electrons in metals

The weak nonlinear response of a metal to the action of low-intensity laser radiation was studied under the normal skin-effect conditions. We have shown that temperature variations with a double frequency emerging during the electron heating lead to the generation of the third harmonic of the fundamental wave. The density of the radiation flux at the tripled frequency was calculated. By measuring this flux one can determine the frequency of the electron-electron collisions with the umklapp of the quasimomentum. Talk presented at the oral issue of J. Russ. Laser Res. dedicated to the memory of Professor Vladimir A. Isakov, Professor Alexander S. Shumovsky, and Professor Andrei V. Vinogradov held in Moscow February 21–22, 2008.     

Features of relativistic electron beam-plasma interaction under high beam current

The specific features of the beam-plasma instability in waveguide under very high beam current are shown analytically. The differences (as compared to conventional case of beam-plasma instability under low beam current) are due to change of physical mechanisms of beam-plasma interaction.