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Contributions to Plasma Physics

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ISSN (Print) 0863-1042 - ISSN (Online) 1521-3986
Published by John Wiley and Sons

[1587 journals]

Radiation Emission of Fast Electrons in Collisions with “Ion‐Sphere” in Dense Plasmas
- Authors: V. A. Astapenko; F. B. Rosmej, V. S. Lisitsa, Xiangdong Li
  Pages: n/a - n/a
  Abstract: Radiative emission of fast electrons in collision with an “ion‐sphere” electron distribution in dense plasmas is under consideration. The electron structure of the ion sphere is calculated ab initio using self‐consistent solution of both bound and free electron distribution inside the sphere. Two radiation channels are included: emission of the colliding electron itself in static potential (conventional or static Bremsstrahlung) and the emission of “ion sphere” medium due to its polarization by the colliding electron (polarization Bremsstrahlung). The last one is calculated in the frame of local plasma density approximation. Interference between conventional and polarization Bremsstrahlung is taken into account. It is shown that spectral cross section of the process has characteristic features depending on plasma density and ionization stage of plasma ions. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
  PubDate: 2013-02-26T06:10:29.845744-05:
  DOI: 10.1002/ctpp.201300002
A Report on H mode in Magnetic Pole Enhanced Inductively Coupled Nitrogen Plasmas
- Authors: F. Jan; A. W. Khan, A. Saeed, M. Zakaullah
  Pages: n/a - n/a
  Abstract: The properties of low pressure magnetic pole enhanced, inductively coupled nitrogen plasma were studied by using electrical probe (Langmuir probe) under the conditions of RF powers in the range of 50‐220 W and pressures of 15‐75 mTorr. The electron energy probability function (EEPF) and electron density (ne) obtained from the RF compensated Langmuir probe was compared with the theoretical results. The theoretical fits of the EEPF shows that the shapes of EEPF are evolved from generalised distribution to Maxwellian distribution function. It was also observed that at a low power (50 W) the discharge remains in inductive (H‐mode) mode for all the pressures (15‐75 mTorr). At a higher pressure and relatively low RF power, the measured EEPF show a hole near 3eV of energy. The intensities of the emission lines at 337.1nm (Second Positive System) and 391.4 nm (First Negative System) due to C3Πu → B3Πg and B2$\textstyle \sum_u^+$ → X2 $\textstyle \sum_g^+$ transitions respectively, closely follows the variation of ne with RF power and filling gas pressure. The stability of the H mode was also investigated using skin depth. Electron temperature and plasma potential indicate that the discharge at higher power (above 50 W) almost remain in H mode. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
  PubDate: 2013-02-26T06:10:23.376469-05:
  DOI: 10.1002/ctpp.201200019
Double Electrical Layer at the Plasma‐Solution Interface
- Authors: A. Khlyustova; A. Maksimov
  Pages: n/a - n/a
  Abstract: Plasma‐solution interface plays the important role in the systems of the electrical discharges with or in liquids (electrolyte solutions). Processes, which pass at this interface, influence on as plasma as liquid. In this paper, the theoretical and experimental results of studies of the double layer on the liquid surface are presented. Data of cathode region properties, kinetics of nonequilibrium vaporization, correlation between radiation intensity and fluxes from electrolyte cathode surface and energy consumptions per on one water molecule transfer are summarized. It is able to suggest the transfer mechanism at the plasma‐solution interface. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
  PubDate: 2013-02-26T06:10:18.320615-05:
  DOI: 10.1002/ctpp.201200105
On the Role of Capacitance Determination Accuracy for the Electrical Characterization of Pulsed Driven Dielectric Barrier Discharges
- Authors: A. V. Pipa; T. Hoder, R. Brandenburg
  Pages: n/a - n/a
  Abstract: A dielectric barrier discharge (DBD) of coaxial geometry has been investigated. The discharge cell was filled by 100 mbar of argon and driven by positive square voltage pulses with a rise time of 20 ns and 75 ns. The internal discharge characteristics such as the discharge current, the gas gap voltage, the instantaneous power and energy have been determined from measured current and voltage waveforms. The peculiarities of the experimental evaluation of the discharge parameters are discussed in detail. Special attention is paid to the accurate experimental determination of the key capacitance values of the DBD, namely the capacitance of the reactor cell Ccell and the capacitance of the dielectric barriers Cd. The influence of the capacitance value accuracy on precision of electrical characterization is demonstrated and it is shown that a small uncertainty in the Cd value leads to large errors in the evaluation of the gas gap voltage. Nevertheless, the obtained accuracy of the capacitance values allows the reliable comparison of the electrical DBD parameters. These are sensitive to the mode of discharge excitation. The shortening of the voltage rise time leads to the increase of the total and instantaneous energy as well as the peak power dissipated into the discharge. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
  PubDate: 2013-02-26T06:10:12.752137-05:
  DOI: 10.1002/ctpp.201200126
Static and Collective Properties of Dusty Non‐Equilibrium Plasmas
- Abstract: The static dielectric function and dust acoustic waves are considered of non‐equilibrium dusty plasmas. The dynamic characteristics are considered using an effective potential applicable at elevated pressure, but this is not a limitation. A three‐species model capable of describing the collective processes is suggested, and a first order phase transition in such systems is previewed. The OCP static characteristics are calculated within the HNC approach. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Dust Particles Behavior in an Electrodynamic Trap
- Abstract: The behavior of the charged dust particles in the linear Paul trap was simulated by Brownian dynamics for reasonable choice of the particle parameters and trap electrode voltages. Regions of these parameters needed for particle confinement at normal atmosphere conditions (pressure and temperatures) have been obtained. An influence of air viscosity, particle masses and charges, frequency and alternating voltage on regions of confinement were investigated. Obtained regions of the particle confinement agree with our experimental results for linear Paul trap. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Glow Discharge Positive Column with Dust Particles in Neon
- Abstract: Experimental and numerical study of positive column of glow discharge in neon with dust particles is presented. The influence of dust structures on integral parameters was measured and simulated. Spatial distributions of electrons and electric field configuration in presence of dust cloud are represented. The reverse radial electric field direction is shown to appear within the dust cloud at high dust particle concentration. The current‐voltage characteristics of discharge in neon with and without dust particles are represented. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The Diagnostics of Dusty Plasma in RF Discharge by Two Different Methods
- Abstract: This work consists of two parts. First part describes the results of optical spectral diagnostics of dusty plasma of carbonaceous gas mixtures in radio frequency discharge. The change in the emission spectrum of the plasma of mixture of argon and methane with introducing of the dust particles was observed. It was explained by the change in the electron temperature. The same effect was observed in other gases: argon, argon‐hydrogen mixture. The second part is about diagnostics of buffer plasma parameters on the basis of dust structure characteristics obtained in the experiments. The possibility of diagnostics of buffer plasma on the basis of experimental data of microscopic characteristics was shown. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Study of the Dust‐Free Region Near an Electric Probe and the Dust Particles Oscillations in Dusty Plasma
- Abstract: In this paper we consider the behavior of the dust particles around the electric probe with a negative potential. The size of the dust‐free region, which depends on the probe potential, was experimentally determined. Theoretical calculation of the size of the dust‐free region based on the energy balance was performed. Comparison of theoretical estimations with experimental results was made. Also in this work the results of the theoretical investigation of the oscillations of the dust particles based on the Fourier analysis of the velocity autocorrelation functions are presented. It is shown that real and imaginary parts of the spectral function have maximum near the plasma frequency of the dust particles at large values of coupling parameter and small values of friction coefficient. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Structural and Transport Properties of Dust Formation in Plasma of Noble Gases Mixture in Radio Frequency Discharge
- Abstract: In the present paper properties of dust formation in RF discharges of pure helium and helium‐argon mixture are investigated. Analysis of macroscopic properties of dust formation at different pressures of background gas reveals a change of properties of dust formation in the mixture of gases in comparison with discharge in pure helium. As possible mechanisms for observed behavior, a change of ion jet content and a friction of neutral component are considered. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Dielectric Model for Electromagnetic Waves Generated in the E‐Layer of the Earth's Ionosphere by Infrasound
- Abstract: A dielectric model for waves of the Earth's ionosphere is developed. In doing so, in comparison to the wellknown dielectric wave model by R.O. Dendy [1] for homogeneous systems, the stratification of the atmosphere is taken into account. Moreover, within the frame of many‐fluid magnetohydrodynamics also the momentum transfer between the charged and neutral particles is considered. Acoustic‐type waves causing the excitation of electromagnetic waves in the warm, weakly‐collisional E‐layer are introduced in the magnetohydrodynamic system by a fluctuating neutral‐particle component. Models of the altitudinal scales of the plasma parameters and the electromagnetic wave field are derived. In case of the electric wave field, a method is given to calculate the altitudinal scale based on the Poisson equation for the electric field and the magnetohydrodynamic description of the particles. Further, an expression is derived to estimate the temperatur changes in the E‐layer because of the propagation of acoustic‐type wave modes and the generation of the electromagnetic waves. And last not least, a formula is derived to determine the dispersion and polarisation of the excited electromagnetic waves, which is necessary to find quantitative results for the turbulent heating of the ionospheric E‐layer. The electromagnetic waves which may be obtained in the E‐layer by the newly developed dielectric model are, amongst others, Alfvén and magnetoacoustic modes, but also waves of the Farley‐Buneman type. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Influence of Polarization Phenomena on Radial Distribution Function of Dust Particles
- Abstract: A pseudopotential model of intergrain interaction in dusty plasmas is proposed to take into account both the electrostatic polarization and the screening phenomena. The derivation is entirely based on the renormalization theory of plasma particles interaction developed previously. Dust particles are assumed to be conductive such that the polarization phenomenon can strictly be treated in the charge‐image approximation. Such an assumption imposes no restraint on generality of the present consideration because the polarization effects are essential for accurate description of intergrain interaction potential. The pseudopotential model is then used in the hypernetted chain approximation (HNC) for the dust component to obtain the radial distribution function which reveals the non‐monotonic behavior at sufficiently large values of the dust coupling parameter. This can be viewed upon as a short‐ or even long‐range order formation in the dust component of the plasma. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
SAHA‐S Thermodynamic Model of Solar Plasma
- Abstract: The model SAHA‐S based on the chemical picture for the equation of state of the solar plasma is presented. The effects of Coulomb interaction, exchange and diffraction effects, free electron degeneracy, relativistic corrections, radiation pressure contributions are taken into account. The solar model based on SAHA‐S taking into account extended element composition and variation of heavy element abundance is represented and discussed. The comparison of the SAHA‐S equation of state data for a hydrogen plasma with the results of other models applicable to the description of the solar plasma equation of state and the results obtained with the first principle methods are demonstrated and discussed. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Electron Screening Effect on Stellar Thermonuclear Fusion
- Abstract: We study the impact of plasma correlation effects on nonresonant thermonuclear reactions for various stellar objects, namely in the liquid envelopes of neutron stars, and the interiors of white dwarfs, low‐mass stars, and substellar objects. We examine in particular the effect of electron screening on the enhancement of thermonuclear reactions in dense plasmas within and beyond the linear mixing rule approximation as well as the corrections due to quantum effects at high density. In addition, we examine some recent unconventional theoretical results on stellar thermonuclear fusions and show that these scenarios do not apply to stellar conditions. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optical Properties of Kelbg‐Pseudopotential‐Modelled Plasmas
- Abstract: Simulation data on hydrogen‐like plasmas, modelled with the Kelbg pseudopotential, are treated within the classical theory of moments. The possibility is analyzed for the model inverse dielectric function to satisfy five convergent sum rules and other exact relations. The sum rules are the power frequency moments of the loss function and the latter are calculated using the hypernetted chain approximation with the Kelbg interaction potential. An approach to the reconstruction of the Nevanlinna parameter function is proposed and successfully tested against the simulation data. Conclusions on the applicability of the Kelbg potential are drawn and a model is put forward to define the Coulomb dielectric function with the space dispersion taken into account. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Characterizing the Structure of Giant Planets
- Abstract: Advances in understanding the structure of giant planets are happening quickly on multiple fronts. New first‐principles equations of state calculations and cutting edge experiments for hydrogen, helium, water, and other planetary materials, are dramatically changing our view of the interior structure and thermal evolution of Jupiter, Saturn, Uranus, and Neptune. The field of transiting exoplanets has led to the addition of over 200 giant planets that can be studied is some detail, as their masses, radii, and bulk densities can be measured. This opens up the possibility of comparing and contrasting our own giant planets to these exoplanets, to better understand giant plants as a class of astrophysical object. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Dynamic Screening, Coulomb Singularity and Drude Model of Absorption
- Abstract: The Debye screening potential is generalized for an arbitrary isotropic distribution function and the dynamic screening for a cold streaming plasma is calculated. In both cases the structure of the screening length is the same, however the potentials are different. For the warm plasma under arbitrary drift the ballistic model is compared with the self consistent dielectric model. The validity of the Drude ansatz is shown to hold as long as the electron oscillations parallel to its motion are negligible. Their energy is by twice the Coulomb logarithm lower than in perpendicular direction. Finally, the problem of the Coulomb singularity is addressed. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Comparative Study on Ion‐Dynamics for Broadening of Lyman Lines in Dense Hydrogen Plasmas
- Abstract: Broadening of spectral lines by a plasma surrounding can be used for plasma diagnostics. Full hydrogen Lyman line profiles are calculated with a quantum‐statistical approach. The effects of plasma electrons and ions on the emitter states are considered separately. The influence of electrons is considered in a dynamically screened Born approximation (collision approximation). For the ions, we apply the quasi‐static approximation and two different approaches to account for ion‐dynamics, namely, the model microfield method (MMM) and the frequency fluctuation model (FFM). We compare resulting widths of Lyman lines in the temperature range T = 104 to 107 K and the free electron density range ne = 1023 to 1026 m–3. For Lα, the error made by neglecting ion‐dynamics increases with increasing temperature and decreasing density, and is at least –15%. Due to the double peaked structure of Lβ the situation is less systematic. However, a large region exists, where ion‐dynamics does not affect the line shape of Lβ. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Electron Transport Mediated by Nonlinear Excitations in Atomic Layers
- Abstract: We study the quantum dynamics in tight‐binding approximation (TBA) of an electron interacting with a classical nonlinear lattice of atoms. By computer simulations we show the existence of fast and nearly loss‐free motions of electrons along crystallographic axes of a two‐dimensional dynamic triangular lattice. Moving bound states between electrons and lattice solitons are formed. These so‐called solectrons allow to transfer charge which initially is localized at certain site to a different place along the same crystallographic axis, with negligible spreading of probability density. The relation to experimental findings about controlling electrons by surface acoustic waves (SAW) in piezoelectric materials is pointed out. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Low‐Density Equation of State for Water from a Chemical Model
- Abstract: We calculate the free energy and other basic thermodynamic properties of water within a model in the chemical picture. The respective mass‐action laws between several molecular, atomic, and ionic species are solved analytically, and purely temperature‐dependent partition functions are used for all species. It is shown that such an ideal gas‐like model is able to describe the thermodynamic properties in relatively good agreement with ab initio simulations, provided that the density of the system is sufficiently low. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Electron Kinetics in Femtosecond X‐Ray Irradiated SiO2
- Abstract: A theoretical study of the ultrafast electron kinetics in solid SiO2, irradiated with a femtosecond X‐ray laser pulse, is presented. A Monte Carlo code for event‐by‐event simulations of individual particles is applied to model the electron kinetics within the irradiated SiO2 bulk. The simulation includes photoionization, elastic and inelastic scatterings of electrons, Auger decays of core holes, and electron‐hole recombination via exciton self‐trapping mechanism. Transient electron density is followed, at different photon energies and pulse durations. The change of the optical properties (reflectance, transmittance) of the material is estimated with the help of the Drude model. The analysis of the results allows us to conclude that within the X‐ray excited dielectric, the holes in the valence band give the predominant contribution to the transient changes of optical properties within the material. The increase rate of the free electron density is limited by the duration of secondary electron cascading. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The Electron Transport Coefficients of Boron and Silicon Plasma
- Abstract: The conductivity, thermal conductivity and thermal power of Silicon and Boron plasma have been calculated within the relaxation time approximation. The plasma composition has been obtained by means of correspond‐ing system of coupled mass action laws. We have considered the atom ionization up to +4. The results of our simulations are in good agreement with recent measurement data at T ≥ 10 kK. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Benchmark of Simplified Formulations for the Electrical Conductivity of Non‐Ideal Plasmas
- Abstract: We discuss simplified formulations for the electrical conductivity [1] and compare them with experimental results of various expanded metals recently published [2]. We use formulations designed for fully ionized hydrogen in a broader range of non‐fully ionized materials of various atomic number through the use of an effective coupling parameter based on estimations of the ionization. The ionizations are deduced from average‐atom calculations and compared with faster Thomas‐Fermi‐Dirac estimations. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Thermodynamic Properties and Electrical Conductivity of Water Plasma
- Abstract: Composition, thermodynamic properties, and electrical conductivity of water plasma are calculated under the assumption of thermodynamic equilibrium. The plasma composition is calculated by stoichiometric approach in which chemical reactions and multiple ionizations are formulated by following mass action law and Saha's equation, respectively. Correction for weakly non‐ideal behavior at high density regime is conducted using the Debye‐Hückel theory. Based on the calculated composition, the electrical conductivities of water plasma, which is the most important parameter for various applications of pulsed spark discharges in water, are calculated at various mass densities and temperatures with the consideration of both electron‐neutral and electron‐ion collisions. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Atomistic Modelling and Simulation of Warm Dense Matter. Conductivity and Reflectivity
- Abstract: Warm dense matter conductivity and reflectivity are investigated by means of density functional theory. Both one‐ and two‐temperature cases are considered. One‐temperature mode is related to equilibrium state where temperature of electrons and ions are equal. As an example of one‐temperature system xenon plasma is studied. The reflectivity of shock‐compressed dense xenon plasma is calculated and compared with experimental data. Two‐temperature mode is associated with different temperature of electrons and ions. The thermal conductivity of aluminium and gold in such mode is examined. The comparison of obtained results with theoretical model based on Boltzmann equation is conducted. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Composition of Dense Beryllium, Boron and Carbon Plasmas
- Abstract: In the present paper we determine the composition of dense beryllium, boron and carbon plasma by solving the Saha equations with corrections due to non‐ideality. The lowering of the ionization potentials is calculated on the basis of effective potentials by taking into account screening and quantum diffraction effects. The considered range of density and temperature covers plasmas with a very low degree of ionization up to full ionization with ions having the maximum ionization state. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Hypernetted Chain Calculations for Multi‐Component and NonEquilibrium Plasmas
- Abstract: We solve the Ornstein‐Zernike equation within the hypernetted chain approximation for dense multi‐component plasmas using effective pair potentials. The method is used to study structural properties of plasmas, for instance in order to explain and predict X‐ray Thomson scattering spectra. Corresponding experiments are performed at free electron lasers such as FLASH Hamburg and LCLS Stanford, or at facilities using energetic optical lasers such as Omega in Rochester and Janus in Livermore. Results for pair distribution functions and static structure factors for dense hydrogen, beryllium, carbon and carbonhydride plasmas are presented. Furthermore, calculations for non‐equilibrium two‐temperature plasmas are performed as well, which are relevant for laserplasma interaction and relaxation phenomena on short time scales. We propose a consistent treatment for the electron‐ion coupling term which leads to a more realistic description of correlation effects. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Temperature‐Dependent Quantum Pair Potentials and Ionization in Helium‐Like Plasmas
- Abstract: Diffraction corrected effective and Coulomb electron‐ion interactions are worked out for helium‐like ions in plasmas of warm dense matter concern, through explicit wave functions derived within a suitable quantum defect frame work. Very significant departures from the corresponding and usual hydrogen‐like expressions are reported. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Ion Beam Driven High Energy Density Physics Studies at FAIR at Darmstadt: The HEDgeHOB Collaboration
- Abstract: High Energy Density (HED) physics spans over numerous areas of basic and applied physics, for example, astrophysics, planetary physics, geophysics, inertial fusion and many others. Due to this reason, it has been a subject of very active research over the past many decades. Static as well as dynamic methods have been applied to generate samples of HED matter in the laboratory. The most commonly used tool in the static techniques is the diamond anvil cell while the dynamic methods involve shock compression of matter. During the past fifteen years, great progress has been made on the development of bunched intense particle beams that have emerged as an additional new tool for studying HED physics. In this paper we present two experiment designs that have been worked out for HED physics studies at the Facility for Antiprotons and Ion Research (FAIR) at Darmstadt. This facility has entered into construction phase and will provide one of the largest and most powerful particle accelerators in the world. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Calculation of Canonical Properties of a Quantum System by Path Integral Numerical Methods
- Abstract: We propose a new approach in obtaining the partition function of a system of several interacting particles (fermions) in external field within path integral Monte Carlo method based on direct averaging of the exchange contributions over the positive weight determined by non‐closed trajectories. This procedure is performed at fixed temperatures, ranging to rather low values. The complete partition function for each temperature is then obtained within an expanded ensemble procedure. We found a good agreement of data obtained by the new method with results of previously proposed path‐integral‐expanded‐ensemble Monte Carlo calculations [1, 2]. The new approach allows to reach observably lower temperatures compared to method [1, 2], thus providing a significant reduce of the sign problem. It yields an independent way to treat thermal properties of quantum systems, so the good agreement with previous data [1, 2] allows us to test and state the validity of both approaches. Simulations for systems of 2 up to 5 non‐interacting particles and particles interacting with Coulomb repulsion in 3D harmonic field were performed. The presented approach allows one to carry out calculations for low temperatures that makes it possible to extract data for the ground‐state energy and low‐temperature thermodynamics. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Issue Information Picture: Contrib. Plasma Phys. 4–5/2013
Contents: Contrib. Plasma Phys. 4–5/2013
Preface: Contrib. Plasma Phys. 4–5/2013
Spatially Resolved Electronic Correlations in Nanoclusters
- Abstract: Recent experimental developments in the creation and diagnostic probing of metallic nanoclusters has made it possible to explore their interaction with electromagnetic radiation, thus revealing information on their electronic properties. Free electrons inside such clusters occupy a very small volume so their characteristics may exhibit significant differences to bulk matter in a similar thermodynamic state. Using high‐resolution molecular dynamics simulation, we study electronic correlations of laser‐excited, sodium‐like nanoclusters. To cover a broad range from nano‐ to microscale, the momentum autocorrelation function is evaluated for systems ranging from 150 to more than half a million electrons. The Coulomb force computation is accelerated by utilizing the parallel Barnes‐Hut tree code PEPC. Complex electronic resonances are found for finite‐sized clusters which do not appear in bulk systems. Analysis of these oscillation modes with a new diagnostic technique show that these are located in different spatial regions within the clusters. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Size Dependence of Minimum Charge of Excited Nano‐Plasmas
- Abstract: The charge of ionized metal clusters is investigated at high temperatures. Molecular Dynamics (MD) simulations are applied to describe the particle motion. While the electrons are treated as separate particles, the interaction with the ion cores is described as an external jellium potential. The final cluster charge is determined by classifying the particles into free and bound electrons. A relation between the cluster charge and cluster sizes as well as temperatures is derived from MD simulations and simple kinetic model calculations. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Cover Picture: Contrib. Plasma Phys. 4–5/2013
- Abstract: Particle‐in‐cell simulations for a liquid hydrogen droplet of 10 micrometer diameter that is irradiated (from left) with an ultra‐short laser pulse (duration 90 fs FWHM, wavelength 800 nm, energy 20 mJ, spot size 100 micrometer FWHM). The snapshot is taken 125 fs after the maximum of the laser pulse. The red region below the surface represents the hot plasma generated by the laser, while the interior of the droplet is still cold (blue). The temporal evolution of such inhomogeneous plasmas is studied at free electron laser facilities such as FLASH with x‐ray Thomson scattering. From: P. Sperling, PhD Thesis, University of Rostock, 2013. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
ESTELL: A Quasi‐Toroidally Symmetric Stellarator
- Abstract: This work presents the physics design for a simple quasi‐axially symmetric stellarator. A plasma configuration described by a modest number of Fourier coefficients was found to establish this symmetry with good accuracy. The low rotational transform results in a relatively simple coil set exhibiting low curvatures and comfortable clearance between adjacent coils. As another consequence, the maximum achievable plasma pressure will be limited to about 0.5%. An experiment along the lines proposed would allow an exploration of the confinement properties of a quasi‐axially symmetric configuration. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)