Dynamic characteristics of strongly coupled classical one-component Coulomb and Yukawa plasmas are obtained within the nonperturbative model-free moment approach without any data input from simulations so that the dynamic structure factor (DSF) satisfies the first three nonvanishing sum rules automatically. The DSF, dispersion, decay, sound speed, and other characteristics of the collective modes are determined using exclusively the static structure factor calculated from various theoretical approaches including the hypernetted chain approximation. A good quantitative agreement with molecular dynamics simulation data is achieved. . SCPs and warm dense matter are highly relevant model systems for inertial fusion devices [6]. The common property of SCPs is that the interparticle potential energy dominates over the thermal energy. Many of the above-mentioned systems have been analyzed and their characteristic effects became understood within the framework of a seminal model system, the one-component plasma (OCP) model that considers explicitly only one type of charged species, while the presence and the effects of other charged species are expressed by the interaction potential φðrÞ.SCPs, as many-body dynamical systems, exhibit various collective excitations, of which the properties have been investigated both via theoretical approaches and numerical simulations. Numerical approaches provide direct access to the central quantity of collective effects, the dynamic structure factor (DSF). The most successful theoretical approach capable of describing strongly coupled plasmas, the quasilocalized charge approximation [7], is able to predict [from the static pair distribution function (PDF)] the dispersion relations of the collective modes; however, it cannot predict the lifetime (decay) of the modes and the form of the DSF itself. Here we demonstrate that the method of moments theoretical approach [8] is able to predict the form and structure of the DSF of the OCP, based on static data only, i.e., the PDF or the static structure factor (SSF). As both the PDF and the SSF can be obtained theoretically as well [e.g., within the hypernetted chain (HNC) approximation and its modifications including the bridge function] the present approach provides a purely theoretical access to the full DSF and a full quantitative description of the collective modes, including their decay and other characteristics, without the necessity to use simulation data as input, as it was done in [9,10].The moment approach is nonperturbative, nonparametric, and model free. Thus it is perfectly applicable to a broad class of fluids characterized by response functions like semidegenerate multicomponent Coulomb systems or even simple liquids. Because of the rigorous mathematical background, the method is based on automatic satisfaction of sum rules and other exact relations. An empirical guidance is plugged directly into the intermediate step of theoretical computations, thus closing the approach and permitting us, in addition, to determine the dynamic...

The formation of visible layered structures that develop at the anodic zone of a constricted glow discharge is reported. They are composed of several tridimensional double layers with axial symmetry enclosing different plasma coronas. The dependence of the number and size of plasma shells with the conditions of the discharge is discussed, as well as the nature of these double layers. The experimental results evidence the effect of the distribution of neutrals in the volume of the discharge for the development of double layers.

The electron attracting plasma sheath adjacent to the surfaces of a positively polarized electrode transforms into an anodic double layer over a threshold bias potential. The proposed one-dimensional model for this transition considers the contribution of the low production of charges by electron impact in the sheath, which develops a positive space charge in front of the electrode. The stationary electric field of this ionizing plasma sheath as well as the plasma potential spatial profile are obtained from the numerical solutions of a nonlinear integral equation derived from the Poisson equation. The stationary transition process is governed by a bifurcation driven by the bias potential of the electrode, which is the parameter controlled in the experiments. Below a bias potential threshold a single and stable ionizing plasma sheath is obtained. Past this critical voltage two possible values are found for the electric field close to the surface of the electrode. The double layer space plasma profile corresponds to low electric fields while a ionizing plasma sheath is found for higher values. It is conjectured that the abrupt transition occurs when the plasma sheath becomes unstable for bias voltage over a threshold and the double layer develops. The discontinuities in the current voltage characteristic curves observed in the experiments as the double layer upsurges or disappears would be explained as jumps between the two possible branches of this bifurcation.

The interaction between an electron emissive wall, electrically biased in a plasma, is revisited through a simple fluid model. We search for realistic conditions of the existence of a non-monotonic plasma potential profile with a virtual cathode as it is observed in several experiments. We mainly focus our attention on thermionic emission related to the operation of emissive probes for plasma diagnostics, although most conclusions also apply to other electron emission processes. An extended Bohm criterion is derived involving the ratio between the two different electron densities at the potential minimum and at the background plasma. The model allows a phase-diagram analysis, which confirms the existence of the non-monotonic potential profiles with a virtual cathode. This analysis shows that the formation of the potential well critically depends on the emitted electron current and on the velocity at the sheath edge of cold ions flowing from the bulk plasma. As a consequence, a threshold value of the governing parameter is required, in accordance to the physical nature of the electron emission process. The latter is a threshold wall temperature in the case of thermionic electrons. Experimental evidence supports our numerical calculations of this threshold temperature. Besides this, the potential well becomes deeper with increasing electron emission, retaining a fraction of the released current which limits the extent of the bulk plasma perturbation. This noninvasive property would explain the reliable measurements of plasma potential by using the floating potential method of emissive probes operating in the so-called strong emission regime.

An analytical expression is derived for the electron thermionic current from heated metals by using a non equilibrium, modified Kappa energy distribution for electrons. This isotropic distribution characterizes the long high energy tails in the electron energy spectrum for low values of the index K and also accounts for the Fermi energy for the metal electrons. The limit for large K recovers the classical equilibrium Fermi-Dirac distribution. The predicted electron thermionic current for low K increases between four and five orders of magnitude with respect to the predictions of the equilibrium Richardson-Dushmann current. The observed departures from this classical expression, also recovered for large K, would correspond to moderate values of this index. The strong increments predicted by the thermionic emission currents suggest that, under appropriate conditions, materials with non equilibrium electron populations would become more efficient electron emitters at low temperatures.