Nonlinear Evolution of Driven Electron Plasma Oscillations in Inhomogeneous Plasmas

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Electronic detection of collective modes of an ultracold plasma

Using a new technique to directly detect current induced on a nearby electrode, we measure plasma oscillations in ultracold plasmas, which are influenced by the inhomogeneous and time-varying density and changing neutrality. Electronic detection avoids heating and evaporation dynamics associated with previous measurements and allows us to test the importance of the plasma neutrality. We apply dc and pulsed electric fields to control the electron loss rate and find that the charge imbalance of the plasma has a significant effect on the resonant frequency, in excellent agreement with recent predictions suggesting coupling to an edge mode.     

Large Volume and High Density Surface Wave Plasmas Sustained by Two Microwave Launchers

Surface wave plasma （SWP） is an electromagnetic excitation along the planar interface between a dielectric and plasma medium when plasma density is so large that its permittivity becomes negative. An experiment SWP system consisting of two microwave launchers （upper and side microwave launcher） has been developed for producing large volume surface wave plasmas in our laboratory. The experimental investigation shows that comparable uniformity plasma with not only large volume but also high density properties has been obtained by the two launchers.     

Torque-balanced high-density steady states of single-component plasmas

Electron plasmas in a Penning-Malmberg trap are compressed radially using a rotating electric field (the "rotating-wall technique"). For large electric fields, plasmas can be compressed over a broad range of frequencies. This permits access to a novel high-density regime in which outward transport is insensitive to plasma density. The limiting density occurs when the plasma rotation frequency equals the rotating-wall frequency. Characteristics of the resulting torque-balanced steady states are described, and implications for high-density electron and positron plasma confinement are discussed.     

Plasmas meet plasmonics

The term ‘plasmon’ was first coined in 1956 to describe collective electronic oscillations in solids which were very similar to electronic oscillations/surface waves in a plasma discharge (effectively the same formulae can be used to describe the frequencies of these physical phenomena). Surface waves originating in a plasma were initially considered to be just a tool for basic research, until they were successfully used for the generation of large-area plasmas for nanoscale materials synthesis and processing. To demonstrate the synergies between ‘plasmons’ and ‘plasmas’, these large-area plasmas can be used to make plasmonic nanostructures which functionally enhance a range of emerging devices. The incorporation of plasma-fabricated metal-based nanostructures into plasmonic devices is the missing link needed to bridge not only surface waves from traditional plasma physics and surface plasmons from optics, but also, more topically, macroscopic gaseous and nanoscale metal plasmas. This article first presents a brief review of surface waves and surface plasmons, then describe how these areas of research may be linked through Plasma Nanoscience showing, by closely looking at the essential physics as well as current and future applications, how everything old, is new, once again.     

Kinetic temperature and charge of a dust grain in weakly ionized gas-discharge plasmas

Analytical relations are given for estimating the energy of the stochastic motion of an individual dust grain heated by electrostatic ion oscillations in a weakly ionized gas-discharge plasma. Dust grain charging processes are analyzed, and an empirical approximation is obtained for the ion current to the grain surface. The processes are simulated under conditions similar to those of laboratory experiments on dusty plasmas. It is found that the kinetic temperature of a dust grain heated by electrostatic ion oscillations in a gas-discharge plasma can exceed the background gas temperature.     

Observations of Nonlinear Behavior in a Low-Pressure Discharge Column

Sudden and abrupt jumps in the plasma density and discharge current of low-pressure magnetized argon and helium plasmas are observed. These jumps are found to depend on the discharge bias voltage, the neutral gas pressure, and the magnetic field strength and occur with a substantial hysteresis in those parameters. These jumps are accompanied by the onset of intense and coherent low-frequency plasma oscillations. In addition, under certain conditions, the radial density profile of the plasma is found to be significantly different following a jump. Some possibly related plasma instabilities are discussed.     

An analysis of acoustic oscillations in dust plasma structures

Low-frequency oscillations in the density of dust particles, which are spontaneously excited in the standing plasma column of a dc glow discharge in neon, were experimentally studied. The longitudinal waves were monitored by a special visualization technique, and the dust sound oscillation characteristics were determined and analyzed using specially developed algorithm and data processing software. It was established that the longitudinal waves propagate from anode to cathode, the frequency and wavevector of the dust sound oscillations being dependent on the discharge current, gas pressure, particle density in the dust cloud, and spatial coordinates. Two-dimensional (2D) fields of the main wave characteristics were studied using an original algorithm. The possible mechanisms of excitation of the dust sound oscillations is discussed. The experimental spatial distributions of the wave parameters are compared to the patterns obtained within the framework of various theoretical models.     

Generation of Uniform Plasmas for Beat Wave Experiments

The laser plasma "beat wave" mechanism for the generation of ultrahigh electric fields requires plasmas of several meters length with density uniformity of about 1 percent. Multiphoton ionization of molecular hydrogen gas at a pressure of a few torr provides a scalable mechanism for generating these plasmas using the same laser beams that drive the beat wave. We describe measurements of electron density, temperature, and uniformity of plasmas generated by a frequency doubled Neodymium glass laser, at an irradiance of about 1014 W · cm-2. The plasma density corresponds to 100-percent ionization and is measured to be uniform to within the measurement errors over a length of 8 mm.     

含温有界原子模型下电子与离子碰撞激发和电离截面的理论研究

采用扭曲波玻恩交换近似方法，在自由原子模型下计算了电子与离子碰撞激发、电离截面，计算值与实验一致；在含温有界平均原子模型下，系统研究了不同温度、密度等离子体中离子的电子碰撞直接电离截面，发现由于温度、密度效应导致离子的能级漂移，引起等离子体中离子的碰撞电离截面比自由原子情形发生较大变化. 关键词： 平均原子模型 扭曲波波恩交换近似 电离截面     

Thomson散射诊断技术的新进展

Thomson散射是一种主动而无干扰地对等离子体进行诊断的方法．它能够以较高的时空分辨率测量等离子体的参数，如电子与离子温度、密度以及等离子体的膨胀速度、电离程度、热流等参数．文章从Thomson散射基本概念出发，介绍了Thomson散射诊断方法在研究激光与等离子体相互作用中的重要意义，并分别介绍了近年来Thomson散射诊断技术的新进展，如对高Z等离子体、两种离子种类的等离子体、多种形态等离子体以及高密度等离子体的研究．文章最后对国内Thomson散射诊断技术的发展状况进行了简述．     

[Russian Text Ignored]

The stability of the electromagnetic plasma confinement by powerful external s-polarized pump waves is considered. The parametric excitation of standing electromagnetic waves along the plasma boundary with frequencies close to the frequency of the pump wave leads to a periodic density modulation of the plasma boundary. The density disturbances along the direction of the external wave field are connected to the excitation of transverse p-polarized surface waves while the modulation in the direction perpendicular to the pump field are created by the parametric interaction between the external wave and s-polarized trapped leaking oscillations. Only when the leaking waves are excited the scale length of the modulation is larger than half the free space wave length of the incident radiation.     

Corona discharge as a temperature probe of atmospheric air microwave plasma jet

We developed and tested a new method for temperature measurements of near-LTE air plasmas at atmospheric pressure. This method is specifically suitable for plasmas at relatively low gas temperature (800–1700 K) with no appropriate radiation for direct spectroscopic temperature measurements. Corona discharge producing cold non-equilibrium plasma is employed as a source of excitation and is placed into the microwave plasma jet. The gas temperature of the microwave plasma jet is determined as the rotational temperature of N₂? produced in the corona discharge. The corona probe temperature measurement was tested by the use of a thermocouple. We found a fairly good agreement between the two methods after correcting the thermocouple measured temperatures for radiative losses. The corona probe method can be generally applied to determine the temperature of the near-LTE plasmas and contrary to the thermocouple it can be used for higher plasma temperatures and is not affected by radiative losses and problems of interaction with the microwave plasma and electromagnetic fields.     

Electromagnetic Plasma Modes at ?pe

The problem of the electromagnetic plasma radiation near the electron plasma frequency ?pe is studied in the absence of an external magnetic field. Maxwell's equations together with the fluid equations, which include thermal effects, are solved for an infinite geometry as well as for a finite geometry, and the problem of the eigenmodes at a plasma frequency ? ?pe is studied. The excitation of these modes by a small density relativistic beam is discussed. It is shown that the presence of a small density beam with finite ?o/c (where ?o is the beam velocity and c the velocity of light in a vacuum) in a plasma of finite thermal velocity, can couple linearly the plasma oscillations excited by the beam with the electromagnetic plasma mode at ?pe. It is also shown that surface waves at a frequency ? ?pe can be excited by the beam.     

A method of cyclic canonical variables for calculation of electrostatic plasma waves

A method is derived, in which cyclic canonical variables (the generalized momenta of which are constants of the unperturbed motion) are used, for the calculation of the oscillations of a collisionless plasma in external fields. The plasma and the fields are assumed to be generally inhomogeneous. In the approximation of an electrostatic plane wave propagating in the plasma, a general dispersion equation for a weakly inhomogeneous plasma is then derived. The advantage of this method is in its great simplicity in contrast with the usual approach, where thex, v-representation is used. Moreover, all resuits are given in a simple, symmetric form. The application of this method is especially convenient for plasmas confined by external fields to a finite volume.     

Fluid turbulence in quantum plasmas

Nonlinear fluid simulations are developed by us to investigate the properties of fully developed two-dimensional (2D) electron fluid turbulence in a very dense Fermi (quantum) plasma. We find that a 2D quantum electron plasma exhibits dual cascades, in which the electron number density cascades towards smaller turbulent scales, while the electrostatic potential forms larger scale eddies. The characteristic turbulent spectrum associated with the nonlinear electron plasma oscillations (EPO) is determined critically by a ratio of the energy density of the EPOs and the electron kinetic energy density of quantum plasmas. The turbulent transport corresponding to the large-scale potential distribution is predominant in comparison with the small-scale electron number density variation, a result that is consistent with the classical diffusion theory.     

Quantum effects on propagation of surface Langmuir oscillations in semi-bounded quantum plasmas

The quantum effects on the propagation of surface Langmuir oscillations are investigated in semi-bounded quantum plasmas. The specular reflection method is employed to obtain the dispersion relation of the surface Langmuir oscillations. The results show that the surface Langmuir oscillations can be propagated due to the quantum effects. It is also shown that the quantum effect enhances the propagation velocity. However, in high wave number domains, the group velocity of the propagation of surface Langmuir oscillations decreases with increasing the wave number. In addition, the electrostatic fast surface oscillating mode is found in the semi-bounded cold quantum plasmas.     

Kinetic energy oscillations in annular regions of ultracold neutral plasmas

A study of ion equilibration in annular regions of ultracold strontium plasmas is reported. Plasmas are formed by photoionizing laser-cooled atoms with a pulsed dye laser. The experimental probe is spatially-resolved absorption spectroscopy using the ²S_1/2-²P_1/2 transition of the Sr⁺ ion. The kinetic energy of the ions is calculated from the Doppler broadening of the spectrum, and it displays clear oscillations during the first microsecond after plasma formation. The oscillations, which are a characteristic of strong coulomb coupling, are fit with a simple phenomenological model incorporating damping and density variation in the plasma.     

Enhanced Beat Wave Saturation Amplitude in an Ionizing Plasma

The excitation of a plasma wave by two laser beams, whose frequency difference is near the plasma frequency, is studied in a plasma with a density that is slowly increasing with time due to ongoing ionization as appropriate for experiments done in laser breakdown plasmas. Numerical integration of the relativistic equation for the evolution of the wave amplitude reveals that for a rate of increase of the plasma density of approximately 1017 cm-3/ns at a laser intensity I = 1014 W/cm2, the wave amplitude can rise considerably above the relativistic saturation limit of Rosenbluth and Liu which was obtained for a plasma of constant density. This increase in plasma density compensates the reduction in plasma frequency caused by the relativistic electron mass increase when the wave amplitude is large. The frequency and phase excursions of the plasma wave are reduced for an optimum time increasing density. We find that moderate damping can stabilize both the amplitude and the phase of the plasma wave with respect to the pump.