Nonlinear Effects Related to the Simultaneous Excitation of Three Instabiities in Magnetized Plasma

Experimental results are presented on the nonlinear effects related to the simultaneous excitation of three low‐frequency instabilities in the magnetized plasma column of a Q‐machine, namely the potential relaxation instability, the electrostatic ion‐cyclotron instability and the Kelvin‐Helmholtz instability. The influence of electron drift and magnetic field intensity on appearance, dynamics and mutual interaction of these instabilities was investigated (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of Radial Density Profile on Resonance Absorption in Laser‐Cluster Interaction

The spatial non‐uniformities in the hydrodynamic parameters of an expanding plasma in laser‐cluster interaction plays an important role in determining the region of resonance absorption. It is shown that, in the case of uniform density, the surface resonance at three times the critical density is responsible for laser absorption. However, it is volume resonance at critical density responsible for the laser absorption, if the non‐uniform nature of plasma density inside the hydrodynamically expanding cluster is taken into account (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A Kinetic Code System to Study Impurity Deposition and Fuel Retention in Gaps Between Divertor Tiles

For the purpose of investigating impurity deposition and fuel retention in gaps between divertor tiles, we combine a three‐dimensional Monte Carlo impurity transport code ITCD with a Particle‐In‐Cell Monte Carlo collision code plus a plasma‐surface interaction (PSI) code. The simulation results show that a potential hill formed near the entrance of the gap can prevent the ionized eroded carbon species from entering the gap. It is found that carbon sources for the co‐deposition in gaps are mainly located at the plasma‐closest edges of the gap, and this finding indicates that special measures associated with the engineering issues should be taken to minimize fuel retention in gaps. The smaller scale of carbon sources inside the gap and the existence of the potential hill near the entrance of the gap are the reasons why the eroded carbon species spatial density is lower inside the gap than outside the gap. Through the study on several scenarios with different substrate and plasma temperatures, the simulation with the combined code can deepen the understanding of fuel retention in the codeposited layers in gaps (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Instabilities in Yukawa Liquids

A strongly coupled Yukawa liquid is a system of charged particles which interact via a screened Coulomb interaction and in which the electrostatic energy between neighboring particles is larger than their thermal energy but not large enough for crystallization. Various plasma systems including ultracold neutral plasmas and complex (dusty) plasmas can exist in this strongly coupled liquid phase.Here we investigate instabilities driven by the relative streaming of plasma components in three‐dimensional Yukawa liquids with a focus on complex plasmas. This includes a dust acoustic instability driven by weakly coupled ions streaming through the dust liquid, and a dust‐dust instability driven by the counter‐streaming of strongly coupled dust grains. Compared to the Vlasov behavior we find there can be a substantial modification of the unstable wavenumber spectrum due to strong coupling effects (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Nonideal Plasma Thermodynamics: Separate Account of Short‐ and Long‐Range Interaction

The method is developed to calculate the thermodynamic functions of strongly non‐ideal plasma by separate treating of short‐ and long‐range interaction contributions, the border of the separation depending on the charge number density as ∼n^1/3. The result for one‐component plasma (OCP) reproduce the Monte Carlo results in the overall interval of non‐ideality parameter values. The method is generalized to treat two‐component plasma (TCP) in the most essential range of non‐ideality parameter. The existence of a double‐phase domain in the pressure‐volume plane is discussed.     

Generation of THz Radiation by Laser Plasma Interaction

This paper presents the three wave parametric decay process to generate the Terahertz (THz) radiations in magnetized plasma. The pump wave (Laser beam) is considered in the extraordinary mode (x‐mode), propagating perpendicular to the background magnetic field. This pump wave decays into an upper hybrid wave and a THz wave which is in magnetosonic mode. The appropriate expressions for the coupling coefficients of the threewave interaction and THz wave amplitude have been derived. Subsequently, the growth rate of this decay instability is also calculated. Various laser and plasma parameters were optimized and we report efficiency of the order of ～1.4 × 10^–2 for current scheme. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Stability of surface waves at magnetized plasma – metal interface

The stability of high‐frequency potential surface waves at a dense magnetized plasma – metal interface with respect to a low‐frequency plasma density modulation is studied in the point of view of the surface waves control. The discussion is addressed to the situation, when an external steady magnetic field is directed perpendicularly to the interface. The nonlinear interaction process of the high‐frequency surface wave, its satellites and the low‐frequency plasma density perturbation is investigated. It is shown that the low‐frequency plasma density perturbation can be represented as a superposition of forced waves of surface and volume types and can lead to an additional attenuation of the surface waves. This attenuation arises when the surface wave amplitude exceeds the threshold value. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Plasma Diagnostics Using K‐Line Emission Profiles of Silicon

Modifications of K‐line profiles due to a warm dense plasma environment are a suitable tool for plasma diagnostics. We focus on Si K_α emissions due to an electron transfer from 2P to 1S shell. Besides 2P fine structure effects we also consider the influence of excited and higher ionized emitters. Generally spoken, a plasma of medium temperature and high density (warm dense matter) is created from bulk Si the greater part of atoms is ionized. The high energy of K_α x‐rays is necessary to penetrate and investigate the Si sample. The plasma effect influences the many‐particle system resulting in an energy shift due to electron‐ion and electron‐electron interaction. In our work we focus on pure Si using LS coupling. Non‐perturbative wave functions are calculated as well as ionization energies, binding energies and relevant emission energies using the chemical ab initio code Gaussian 03. The plasma effect is considered within a perturbative approach to the Hamiltonian. Using Roothaan‐Hartree‐Fock wave functions we calculate the screening effect within an ion‐sphere model. The different excitation and ionization probabilities of the electronic L‐shell and M‐shell lead to a charge state distribution. Using this distribution and a Lorentz profile convolution with a Gaussian instrument function we calculate spectral line profiles depending on the plasma parameters. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Modulation instability of lower hybrid waves leading to cusp solitons in electron–positron(hole)–ion Thomas Fermi plasma

Following the idea of three‐wave resonant interactions of lower hybrid waves, it is shown that quantum‐modified lower hybrid (QLH) wave in electron–positron–ion plasma with spatial dispersion can decay into another QLH wave (where electron and positrons are activated, whereas ions remain in the background) and another ultra‐low frequency quantum‐modified ultra‐low frequency Lower Hybrid (QULH) (where ions are mobile). Quantum effects like Bohm potential and Fermi pressure on the lower hybrid wave significantly reshaped the dispersion properties of these waves. Later, a set of non‐linear Zakharov equations were derived to consider the formation of QLH wave solitons, with the non‐linear contribution from the QLH waves. Furthermore, modulational instability of the lower hybrid wave solitons is investigated, and consequently, its growth rates are examined for different limiting cases. As the growth rate associated with the three‐wave resonant interaction is generally smaller than the growth associated with the modulational instability, only the latter have been investigated. Soliton solutions from the set of coupled Zakharov and NLS equations in the quasi‐stationary regime have been studied. Ordinary solitons are an attribute of non‐linearity, whereas a cusp soliton solution featured by nonlocal nonlinearity has also been studied. Such an approach to lower hybrid waves and cusp solitons study in Fermi gas comprising electron positron and ions is new and important. The general results obtained in this quantum plasma theory will have widespread applicability, particularly for processes in high‐energy plasma–laser interactions set for laboratory astrophysics and solid‐state plasmas.     

Investigations of Droplet‐Plasma Interaction using Multi‐Dimensional Coupled Model

Recently developed multi‐dimensional coupled fluid‐droplet model is used to investigate the behavior of complex interaction between the liquid precursor droplets and atmospheric pressure plasma (APP). The significance of this droplet‐plasma interaction is not well understood under diverse realm of working conditions in two‐phase flow. In this study, we explain the implication of vaporization of liquid droplets in APP which are subsequently responsible to control major characteristics of surface coating depositions. Coalescence of water droplets is more dominant than Hexamethyldisiloxane (HMDSO) droplets because of its sluggish rate of evaporation. A disparity in the performance of evaporation is identified in two independent mediums, such as gas mixture and discharge plasma using HMDSO precursor. The length of evaporation of droplets is amplified by an increment of gas flow rate indicating with a reduction in the gas temperature and electron mean energy. In particular, the spatio‐temporal density distributions of charged particles show a clear pattern in which the typical nitrogen impurity ions are primarily effective as compared to other helium ionic species along the pulse of droplets in APP. Finally, we contrast the behavior of discharge species in the pure helium and He‐N2 gas mixtures revealing the importance of stepwise and Penning ionization processes. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Modelling of Carbon Erosion and Transport at Divertor Target Plate Using a Suite of Codes

To investigate carbon‐based material erosion and ensuing eroded carbon species density distribution, a Particle‐In‐Cell Monte Carlo collision code plus a plasma‐surface interaction code were combined with a Monte Carlo impurity transport code ITCD. It is found that a “density hill” forms at a distance of 3‐4 mm from divertor target plate under certain circumstances: high plasma temperature, small incident angle and strength of the magnetic field. By means of the study with the combined code on several scenarios with different plasma temperatures, the incident angles and strengths of the magnetic field, the simulation results reveal that they have a significant influence on the chemical erosion of carbon‐based material and the spatial distribution of eroded carbon species density above divertor target plate: the eroded carbon species density is smaller at a lower plasma temperature; the scenario with smaller incident angle and greater strength of the magnetic field can reduce the chemical erosion of carbon‐based material and the eroded carbon species density above divertor target plate evidently (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Interaction phenomena and effect of higher order dispersion on electron acoustic solitary waves in weakly relativistic regimes

The interaction phenomena of electron acoustic solitary waves (EASWs) and the higher order correction of Korteweg‐de Vries (KdV) equations (KdVEs) have investigated in unmagnetized collisionless plasma system consisting of relativistic cold electrons and electron beams, non‐relativistic Maxwellian hot electrons and stationary ions. To understand the physical issues concerned, the two‐sided KdVEs using extended Poincaré‐Lighthill‐Kue (ePLK) method are derived taking the higher order correction into consideration. The analyses reveal that the widths and amplitudes of EASWs (as obtain from KdVEs) are decreasing with plasma parameters. The plasma parameters are responsible for the modification of KdV‐soliton structure. It is found that the narrowness of width and the steepness of dip of the solitons become more pronounced and the electric field behaves like semi‐kink solitons due to the higher order correction of KdVEs. Dip shape rarefactive soliton becomes pronounced by plasma parameters. The phase shifts of EASWs are also enhanced due to the effects of plasma species temperatures and density ratios.     

The (3+1)‐dimensional dust‐acoustic waves in multi‐components magneto‐plasmas

A three‐dimensional four components magneto‐plasma system consists of super‐thermal κ‐distributed electrons and positrons, Maxwellian ions, and inertial massive negatively charged dust grains is considered to examine the modulational instability (MI) of the dust‐acoustic waves (DAWs), which propagates in such a magneto‐plasma system. The reductive perturbation method, which is valid for small but finite amplitude DAWs, is employed to derive the (3 + 1)‐dimensional non‐linear Schrödinger equation (NLSE). The NLSE leads to the MI of DAWs as well as the formation of dust‐acoustic rogue waves (DARWs) which are formed due to the effects of non‐linearity in the propagation of the DAWs. It is found that the basic features (viz. amplitude and width) of the DAWs and DARWs (which is formed in the unstable region) are significantly modified by the various plasma parameters such as κ‐distributed electrons and positrons, temperatures, and number densities of plasma species, and so on. The application of the results in both space and laboratory magneto‐plasma systems is briefly discussed.     

The Classical Binary and Triplet Distribution Functions for Two Component Plasma

The equilibrium properties of a multi‐component plasma of charged particles that interact through the coulomb and short‐range potentials are investigated. In particular, this article presents density expansions of the reduced distribution functions for more particles, our calculations are based on the Bogoliubov‐Born‐Green‐Kirkwood‐Yvon (BBGKY) hierarchy, we used the results to calculate the binary and triplet distribution functions. We obtained the analytical form of the classical triplet distribution functions for two component plasma; one of them is based on the Kirkwood superposition approximation (KSA) which is consisting of the assumption that the potential in a set of three particles is the sum of the three pair potentials, this is equivalent to assuming that the triplet distribution function is the product of the three radial distribution functions, and the other form is calculated by integration the triplet distribution function (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

THz Radiation Generation via the Interaction of Ultra‐short Laser Pulses with the Molecular Hydrogen Plasma

In this paper, a two dimensional Particle In Cell‐Monte Carlo Collision simulation scheme is used to examine the THz generation via the interaction of high intensity ultra‐short laser pulses with an underdense molecular hydrogen plasma slab. The influences of plasma density, laser pulse duration and its intensity on the induced plasma current density and the subsequent effects on the generated THz signal characteristics are studied. It is observed that the induced current density in the plasma medium and THz spectral intensity are increased at the higher laser pulse intensities, laser pulse durations and plasma densities. Moreover, the generated THz electric field amplitude is reduced at the higher laser pulse durations. A wider frequency range for the generated THz signal is shown at the lower laser pulse durations and higher plasma densities. Additionally, it is found that the induced current density in hydrogen plasma medium is the dominant factor influencing the generation of THz pulse radiation. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Plasma‐Substrate Interaction during Plasma Deposition on Polymers

The initial stage of film growth during plasma deposition on polymers determines many film properties such as morphology and structure, interphase formation and adhesion. Therefore, the plasma‐substrate interaction is investigated regarding the energy density during film growth, which is defined by the energy flux per depositing atom. The flux of film‐forming species and the flux of energetic particles were determined for metal sputtering (silver films) and plasma polymer deposition (amino‐functional hydrocarbon films). It is shown that enhanced energy densities can be obtained during the initial film growth due to reduced deposition rates and mixing with the polymer substrate (interphase formation). Thus, good adhesion on polymers such as polyethylene terephthalate (PET) has been achieved. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Quantum Color Dynamic Simulations of the Strongly Coupled Quark‐Gluon Plasma

A strongly coupled plasma of quark and gluon quasiparticles is studied by combination of Path integral Monte Carlo and quantum Wigner dynamics simulations. This method extends previous classical nonrelativistic simu‐lations based on a color Coulomb interaction to the quantum regime. First results for the momentum‐momentum autocorrelation function and diffusion constant are presented (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Characterization of 6‐propylthiouracil and its interaction with human serum albumin on Au surface by surface‐enhanced Raman scattering

In this study, surface‐enhanced Raman scattering (SERS) spectra of 6‐propylthiouracil (6‐PTU) on Au surface and the interaction between 6‐PTU and human serum albumin (HSA) were studied. The Raman bands were assigned by the density functional theory calculations at the B3LYP/6‐311++g(d,p) level. Furthermore, the effects of concentration on the SERS spectra of 6‐PTU were analyzed. It shows that with the changes of the concentrations of 6‐PTU, the SERS spectra of 6‐PTU present significant changes, and it can be concluded that with the changing of concentrations, the orientation of 6‐PTU on Au surface also changes. In addition, the SERS spectra of the interaction between 6‐PTU and HSA show that the binding sites of 6‐PTU to HSA are the functional groups N3H and CO. The information will not only be references to the study of the mechanism of the interaction between drugs and blood plasma or serum albumin but also a guidance to understand the metabolism of drugs in human body. Copyright © 2015 John Wiley & Sons, Ltd.     

Connection between the Dielectric and the Ballistic Treatment of Collisional Absorption

I this work two important models of treating collisional absorption in a laser driven plasma are compared, the dielectric and the ballistic model. We will see that there exists a remarkable connection between these basic approaches which could give a hint how to overcome the inherent limitations. The approximations made in the models are not identical and lead to different advantages and disadvantages. We notice that the dieletric model is able to handle screening in a selfconsistent manner, but is limited to first order in the electron‐ion interaction. The ballistic model calculates the electron‐ion collision exactly in each order of the interaction, but has to introduce a cut‐off to incorporate screening effects. This means in the context of kinetic theory that the electron‐ion correlation has to be calculated either in random phase or in ladder approximation, or, in other words, the linearized Lenard‐Balescu or Boltzmann collision term has to be used.     

Modeling of terahertz radiation emission from a free‐electron laser

In this article, we report the generation of terahertz (THz) radiation using the interaction of a laser‐modulated relativistic electron beam (REB) with a surface plasma wave. Two laser beams propagating through the modulator interact with the REB, leading to velocity modulation of the beam. This results in pre‐bunching of the REB. The pre‐bunched beam travels through the drift space, where the velocity modulation translates into density modulation. The density‐modulated beam, on interacting with the surface plasma pump wave, acquires an oscillatory velocity that couples with the modulated beam density to give rise to a nonlinear current density which acts as an antenna to give THz radiation. By optimizing the parameters of the beam and the wiggler, we obtain power of the order of 10⁻⁴ using the current scheme.