Condensation mode instability in a heat-releasing weakly ionized gas in a magnetic field

Linear equations and dispersion relations describing the condensation mode in weakly ionized plasma with heat release, being in an external magnetic field, are derived. The conditions of the instability onset of the condensation mode of the ion component are found.     

Current induced Kerr effect in weakly ionized gases in the presence of a magnetic field

The current induced Kerr effect in the presence of a homogeneous magnetic field is treated for binary mixtures of neutral molecules and ions. The starting point is a system of moment equations derived from the linearized Waldmann-Snider equation. The dialectric tensor is calculated and studied in particular for a lorentzian mixture in perpendicular electric and magnetic fields. It is shown that the magnetic field causes a decrease of briefringence as well as a rotation of the principal axes of the dielectric tensor.     

Electron density measurements in a gas discharge subjected to a rotating magnetic field

Measurements of the electron density within an axial CO₂ laser discharge subjected to a transverse rotating magnetic field are presented. Experiments were performed with a single Langmuir probe. Electron density is evaluated using Su and lam's thick sheath expression for a stationary plasma. Results are presented for a 2.7 kPa (20 torr) discharge with external pre-ionization and for a 0.7 kPa (5 torr) self-sustained discharge.     

Kinetic approach to the propagation of electromagnetic waves in a weakly ionized plasma

Summary High-frequency wave phenomena in a partially ionized plasma are analysed in the frame of the kinetic theory without resorting to perturbation techniques. In particular, we obtain the electron distribution function in an external electric field alternating in both time and position, and then the electrical conductivity and the dispersion relation. Corrections to the results of the macroscopic theory are evaluated up to any desired order.

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Riassunto Il fenomeno della propagazione di un'onda elettromagnetica in un plasma parzialmente ionizzato è analizzato nell'ambito della teoria cinetica. Il metodo proposto consente di ricavare la funzione di distribuzione degli elettroni senza dover ricorrere a tecniche perturbative. Si riportano le espressioni esatte della conducibilità elettrica e della legge di dispersione e, quindi, le correzioni da apportare ai risultati ottenuti con la teoria macroscopica.

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Резюме В рамках кинетической теории анализизируется явление распространения электромагнитных волн в частично ионизованной плазме. Предложенный метод позволяет получить электронную функцию распределения во внешнем электрическом поле без использования теории возмущений. Затем определяются электрическая проводимость и дисперсионное соотношение. Поправки к резулятатам макроскопической теории оцениваются в любом желаемом порядке.

     

弱电离等离子体对电磁波吸收的物理模型和数值求解

从物理基本方程、理论证明和数值分析三方面说明了在一维平板模型中，含时波动方程和亥 姆霍兹方程是等价的，即使电磁波波长小于等离子体的尺度，电磁波的全波解也具有简谐形 式. 对电磁波在弱电离强碰撞等离子体中的传播特性进行了数值研究，结果表明，弱电离强 碰撞等离子体对电磁波具有很强的吸收特性. 关键词： 电磁波 弱电离等离子体 过阻尼     

A collisional-radiative model for helium and its application to a discharge plasma

For the collisional-radiative model applied to helium, two alternative formulations are presented in which non-linear process such as ionization due to metastable-metastable collisions may be included. The atomic data, including dielectronic,recombination, employed in the calculations are summarized. The collisional-radiative calculation is applied to a positive-column plasma for which both the nonlinear processes and radiation trapping are taken into account. The calculated population densities of excited levels for a low-pressure and low-current discharge plasma show good agreement with a measurement made using the hook method. The population density distribution among excited levels is interpreted in terms of excitation-ionization mechanisms in the plasma. This leads to a grouping of the excited levels into two phases for the discharge plasma considered: the corona phase applies to the lower-lying levels and the quasi-saturation phase to the higher-lying levels. The importance of the ladder-like excitation-ionization mechanism is noted for this class of plasmas.     

Resonant tunneling in weakly coupled GaAs/AlGaAs superlattices in a transverse magnetic field: A probe of electronic distribution function

A method is proposed to get information about carrier distribution function in superlattices and multiple quantum-well structures from the analysis of the vertical transport experiments in a transverse magnetic field. The method was applied to the GaAs/AlGaAs superlattices with wide quantum wells in strong (B=0–7 T) magnetic fields. It was shown that the distribution function of electron is nonequilibrium Boltzmann-like, with electronic temperature T=10–20 K.     

Impact of nonisotropic elastic and inelastic scattering on the electron velocity distribution in weakly ionized plasmas

Summary By using appropriate angular distributions for elastic and inelastic scattering of electrons with gas atoms, the effect of nonisotropic elastic and/or inelastic collision processes on electron velocity distribution and corresponding macroscopic quantities, and also on their variations when increasing the approximation orders, is studied for a convenient model plasma. The study is made possible by the use of a new technique for the solution of the Boltzmann equation at elevated orders of approximation based on an appropriate Legendre polynomial expansion of the velocity distribution function. It is found that large variations of the distribution function and relevant macroscopic quantities occur when passing from isotropic scattering to narrow angular distributions of forward scattering in elastic collisions or in both kinds of collision processes. The simultaneous action of the two anisotropies leads to a pronounced amplification of the effect while backward scattering produces less important changes. The effects remarkably increase when decreasing the energy loss per inelastic collision. A microphysical interpretation of the impact of nonisotropic scattering is given in terms of the competing actions of field acceleration and collisional dissipation, which is modified by nonisotropic scattering, and of the reflections on the structure of the hierarchy of equations describing the electron behaviour.

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Riassunto Facendo ricorso ad appropriate distribuzioni angolari relative allo scattering elastico ed anelastico di elettroni da parte degli atomi di un conveniente gas modello, è stato studiato l’effetto che processi di collisione elastici e/o anelastici anisotropi hanno su distribuzione elettronica delle velocità e corrispondenti parametri macroscopici, nonché sulle variazioni che dette grandezze macroscopiche subiscono quando viene elevato l’ordine di approssimazione. Lo studio è stato reso possibile dall’uso di una nuova tecnica che permette la soluzione dell’equazione di Boltzmann ad elevati ordini di approssimazione con un’opportuna espansione in polinomi di Legendre della distribuzione delle velocità. è stato così possibile osservare che grandi variazioni sia della distribuzione delle velocità che delle grandezze macroscopiche si hanno allorché si passa da scattering isotropo a scattering marcatamente in avanti nelle collisioni elastiche o in entrambi i tipi d’urto. La simultanea azione delle due anisotropie porta ad una pronunciata amplificazione dell’effetto mentre lo scattering all’indietro produce cambiamenti meno importanti. è stato anche messo in luce come l’effetto dipenda dall’energia persa negli urti anelastici e come esso generalmente aumenti considerevolmente se la perdita anelastica decresce. Viene anche data una interpretazione fisica dell’effetto prodotto dall’anisotropia dello scattering in termini delle azioni competitive del campo e degli urti e dei riflessi che lo scattering anisotropo ha sulla struttura della gerarchia di equazioni che descrivono il comportamento elettronico.

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Резюме Используя соответствующие угловые распределения для упругого и неупругого рассеяния электронов на атомах газа, для обычной модельной плазмы исследуется влияние процессов неизотропных упругих и/или неупругих соударений на распределение электронов по скоростям и на соответствующие макроскопические величины, а также их изменение при увеличении порядка аппроксимации. При исследовании используется новая техника решения уравнения Больцмана в соответствующих порядках аппроксимации, основанная на разложении по полиномам Лежандра функции распределения электронов по скоростям. Получено, что больщие изменения функции распределения и соответствующих макроскопических величин возникают при переходе от изотропного рассеяния к узким угловым распределениям рассеяния вперед в упругих соударениях или в обоих типах процесса соударения. Одновременное действие двух анизотропий приводит к заметному усилению эффекта, тогда как рассеяние назад вызывает менее существенные изменения. Эффект значительно увеличивается при уменьшении энергетических потерь в неупругом соударении. Предлагается микрофизическая интерпретация влияния неизотропного рассеяния в терминах конкурирующих процессов ускорения полем и столкновительной диссипации, которые изменяются за счет неизотропного рассеяния, а также изменений структуры иерархии уравнений, описывающих поведение электронов.

     

Ionic recombination in a weakly ionized gas : I. A stochastic approach to the recombination rate problem

Using the framework of a stochastic approach to the reaction-kinetic problem originating from Teramoto and Shigesada equations for the phase-space evolution of the ionic part in a diluted ternary gas mixture composed of positively and negatively charged ions as well as of neutrals are derived. On the basis of the stationary solution of the reactive ion-pair equation an operator expression for the recombination constant α is defined and discussed with regard to the effect of the center-of-mass motion. By iteration a formally exact α-expansion in terms of multiple ion-pair neutral collisions is derived for the case that non-thermal center-of-mass effects can be neglected. This expansion has to be specified to meet the conditions of well-known models for ion-pair stabilization (absorbing sphere, critical energy barrier).     

Raman scattering from a two-dimensional electron gas in a weakly and periodically modulated magnetic field

An analysis of light scattering from a two-dimensional electron gas (2DEG) subject to aweak periodicmagnetic modulation of strengthB_mand to a perpendicular uniform magnetic fieldBof arbitrary strength is presented. Raman spectra are calculated for (i) electron inter-Landau-level transitions, which result in a Raman shift ∼  2ω_c, and (ii) inter-Landau-level collective electron excitations at a hybridized magnetoplasmon frequency and at anewlow-frequency, intra-Landau-level plasmon mode induced by the modulation. The dependence of the Raman cross sections on the strength ofBandB_mis assessed. The effect of a weakB_mon the Raman spectrum is similar to that of a weak electric modulation but the signals from the magnetically modulated 2DEG are much stronger. The combined effect of the electric and magnetic modulations is also considered.     

弱磁场中弱相互作用费米气体的有限粒子数效应(英文)

由弱磁场中弱相互作用费米气体的配分函数,导出有限粒子数条件下系统的配分函数G(β,N ).在此基础上,运用统计平均方法求解有限粒子数弱相互作用费米气体热力学量的解析表达式,给出各种温度条件下的热力学性质.研究结果表明,有限粒子数效应使各个热力学量都产生了一个修正项,除温度趋于0外,粒子数对化学势的修正项有直接影响,对内能和热容量的修正项并不产生直接影响.并且有限粒子数效应总是降低化学势,从而使化学势的0点向低温漂移,粒子数增大,会削弱这种效应,粒子间的相互排斥会加强这种效应.     

The time dependent electron velocity distribution in a fully ionized gas under the action of electric and magnetic field

The Boltzmann's equation in crossed electric and magnetic fields is solved provided that the electron-electron collisions are neglected. The velocity distribution fucntion is obtained in the analytic form; the runaway rate is calculated in dependence on the magnetic field and time.The author wishes to express his thanks to Prof. J. Kracik, DrSc. for valuable advice and suggestions.     

A combined system for generating a uniform magnetic field and its application in the investigation of Efimov physics

We propose a scheme to produce a uniform magnetic field with a system comprising a pair of coils and an atom chip.After optimizing the parameters of the chip wires, we improve the homogeneity of the magnetic field by two orders of magnitude. We exhibit that this method can be applied in the investigation of Efimov physics in ~(87)Rb-~(40)K mixture.     

A simplified model joining the sheath and the plasma in electronegative plasmas

An extension of the previous work which only dealt with the sheath zone is used to analyze the wall-plasma interaction in electronegative plasmas. Ionization is introduced as the presheath mechanism. This extension includes the joining of the sheath and the plasma solutions. For certain plasma parameters a stratified presheath is obtained. In this case, the plasma and the sheath solutions are matched in a very simplified way, by introducing a discontinuity in the electric field. This discontinuity is equivalent to consideration of a negatively charged layer between the presheath and the sheath. The parameter space region in which this matching should be made has been delimited. The model includes the previous one in the limiting case of no ionization.     

The experimental observation of T-layers in a moving plasma interacting with the magnetic field

This paper presents the experimental results of a study of the interaction of plasma bunches injected from an independent source into a parallel plate rail-tube (Hereafter referred to as a railtron) with the magnetic field decelerating their motion. A process of the formation of the stratified plasma structure regular in character has been detected.