The occurrence and propagation of large amplitude dust-acoustic solitary waves (DASWs) are studied in a three-component plasma consisting of negatively charged dust grains and electron-positron pairs by employing a pseudopotential technique. Here, we focus on a superthermal plasma modeled by a -like distribution and consider a finite temperature for dust particulates. It is shown that the solitary waves with negative polarity are allowed in the system and there is a critical value for dust charge Z d above/below which the subsonic/supersonic solitary structures can propagate. In the case of negative fullerene ions, Z d = 1, it is observed that subsonic DASWs can propagate in the plasma. In addition, it is revealed that the propagation of double layers is not possible in this plasma system.
We study, beyond the well-known Akhiezer-Polovin model, plasma electrostatic wave and unmagnetized electron beam.Our investigation is based on a stricter theory in which a long-lasting misconception about zerotemperature fluid motion equation is removed. Our theory explains some authors' puzzle about why a narrowly focused (charged particles) beam is preserved in the presence of strong space charge forces. The interaction of such a unmagnetized charged particles beam with a plasma electrostatic wave is studied in details and some universal results are revealed. These exact information are crucial to accurate estimation of the quality of a plasma wakefield and hence its performance in acceleration.
Plasma echo theory is revisited and reviewed to apply it to a semi-bounded plasma. Spatial echoes in a semi- bounded plasma are investigated by calculating the electric field produced by external charges and satisfying the boundary conditions at the interface. We show that echoes can occur at various spots. The diversity of echo occurrence spots is due to the boundary terms. x ik e or ) / ( v x t i e . This modulation is called free streaming term since x = vt is the characteristic line of a free particle. This term makes the modulation of the distribution function more and more oscillatory as t or x increases, and consequently, fdv will become vanishingly small due to almost complete cancelations (phase-mixing). Therefore, the free streaming term yields no appreciable effect on macroscopic variable such as density perturbation.
This work introduces a conformal finite difference time domain (CFDTD) particle-in-cell (PIC) method to accurately and efficiently study electromagnetic or radio frequency (RF) structures and their interactions with charged particles.For illustration, the dispersion relation of an A6 relativistic magnetron has been determined and a preliminary hot test including electrons has been done.The accuracy of the CFDTD method is measured by comparing with calculations based on the finite element method.The results show that an accuracy of 99.4% can be achieved by using only 10,000 mesh points with the Dey-Mittra algorithm as implemented in the CFDTD method.By comparison, a mesh number of 250,000 is needed to preserve 99% accuracy using a staircased FDTD method.This suggests one can more efficiently and accurately study the hot tests of microwave tubes or the interactions of charged particles and RF structures using the CFDTD PIC method than a conventional FDTD one.
Whereas the energy loss of ions penetrating cold matter is understood and several theories, codes and tables exist, the interaction with plasma is scarcely investigated and only a few experimental data exist.Therefore the interaction of heavy ions penetrating hot and dense plasma is explored at the GSI Helmholtzzentrum für Schwerionenforschung using powerful lasers to create a plasma and ions from the UNILAC accelerator to probe the target.For the interpretation of the experimental data it is crucial to know the plasma parameters like density and temperature as a function of time and space.Therefore a multiframe laser interferometry has been developed to fulfil the requirements.The set up of the interferometry is presented as well as some results of the free electron density distribution of expanding carbon and aluminium plasma at different times.
In a magnetized inhomogeneous warm plasma having ionization/recombination, usual version of the KdV equation is found to be modified by two additional terms arising due to the inclusion of ionization/recombination and the density gradient in the plasma.The density gradient in the plasma shows its dependence on the ionization/recombination rate, ion-to-electron temperature ratio, obliqueness of the magnetic field and drift velocity of the ions.In the considered plasma, only the compressive solitary structures are found to propagate corresponding to two different types of modes.A significant effect of magnetic field and ion temperature is found on these structures in both the cases of ionization and recombination, though these structures show weak dependence on the charge of the ions.Interestingly the solitons with prominent tailing structures are evolved in the plasma under the effect of stronger density gradient and higher ionization or recombination.The tailing structure with bigger size evolves in the plasma in the case of only recombination, suggesting that the exchange/transfer of energy from the main soliton to its tail is on a greater scale in the case of recombination than the case of ionization.There exists a critical value of the ionization rate at which the tailing structure associated with only the fast (not slow) solitary structure is vanished.Similarly, the tailing structure associated with only the slow (not fast) solitary structure is disappeared at a critical value of recombination rate.
A numerical study is performed to assess the influence of thermochemical nonequilibrium on the transport coefficients used in Computational Fluid Dynamics (CFD) simulations of hypersonic external flowfields.An quantitative assessment is made of transport coefficients from simplified methods of Blottner curve fits and Variable Hard Sphere (VHS) model on the numerical solution of a Mach 23 flow past a sphere cone, the RAMC-II test case.The equations derived by Kustova [1] in the state kinetic approach for calculating transport coefficients from the Chapman-Enskog solution of the Wang-Chang Uhlenbeck equation were used to conduct a parametric study for assessment of the effect of the following parameters on the state-specific diffusion coefficients: (1) Widely different population distributions, (2) Atomic mass concentration, and (3) Binary atomic to molecular diffusion coefficient ratio.The present study is a first step to quantify the relative importance of the parameters considered for a future implementation of the computationally expensive state-kinetic transport coefficients in multi-dimensional fluid dynamic flow solvers for flow conditions where the more general state kinetic approach becomes necessary.
In this paper the importance of using accurate CFD simulations in the design of hypersonic vehicles is stressed.The attention is focused on the one hand on the need to providing the vehicle designer with the estimated error bars together with the nominal values of the design parameters.On the other hand it is underlined how, in the different design phases, different levels of accuracy can be used, from simple inviscid computations to complex viscous non-equilibrium modellization, depending on the problem that must be solved.Then, the attention is focused on the kinetic models, from the classic macroscopic to the advanced models based on the state-to-state approach.Some examples of test cases that were used in the last years to validate CFD codes with respect to the kinetic modeling are presented, with the aim of emphasizing the potential advantages in using the state-to-state approach.Finally, preliminary results of the numerical rebuilding of wind tunnel test cases that are currently being performed in the framework of the Phys4Entry Project for code validation are shown.
The paper presents radiation models developed to investigate radiation in entry in Earth, Mars and Jupiter atmospheres.The capacity of ASTEROID computing code to simulate elementary radiative processes, calculate spectral and groups optical properties, and also solve simple radiative heat transfer problems is presented for Earth entry.The large number of radiative processes involved in the radiative flux is put forward.The contributions of the different radiative processes encountered in Mars entry are studied using the HTGR spectroscopic database.The validity of this database with respect to diatomic molecules systems and CO 2 infrared radiation is illustrated through experimental validations.The accuracy of statistical narrow-band model to predict radiative flux is illustrated for an afterbody.Finally recent improvements of the model developed for the calculation of radiative properties of high-temperature H 2 /He mixtures representative of Jupiter atmosphere is presented.The model takes into account the most important radiative processes.
The physical properties of hot dense matter over a broad domain of the phase diagram are of interest in astrophysics, planetary physics, power engineering, controlled thermonuclear fusion, impulse technologies, enginery, and other applications.The present report reviews the contribution of modern experimental methods and theories to the problem of the equation of state (EOS) at extreme conditions.Experimental techniques for high pressures and high energy density cumulation, the drivers of intense shock waves, and methods for the fast diagnostics of high-energy matter are considered.It is pointed out that the available high pressure and temperature information covers a broad range of the phase diagram, but only irregularly and, as a rule, is not thermodynamically complete; its generalization can be done only in the form of a thermodynamically complete EOS.As a practical example, construction of multi-phase EOS for tungsten is presented.The model's results are shown for numerous shock-wave data, the high-pressure melting and evaporation regions and the critical point of tungsten.
Modern problems of radiative aerothermodynamics of entering space vehicles are demonstrated and analyzed in the paper.New radiative gas dynamic problems concerned to coupling processes of non-equilibrium dissociation with radiation heat transfer in shock layers generated above large scale re-entry space vehicles returning from orbital and super orbital space mission are considered in the first part.Three-dimensional numerical simulation data on radiative aerothermodynamics of Martian entry probes Pathfinder, Exomars and Mars Science Laboratory (MSL) are presented and analyzed in the second part.It is shown that integral radiative heating of leeward surface of the entry probes exceeds corresponding convective heating.The third part is dedicated to consideration preliminary numerical simulation results on radiative gas dynamics of Galileo probes.At first, a review of the available results obtained during the mission preparation and post-flight analyses has been undertaken to select a computational matrix.This matrix has been selected by accounting for previous numerical efforts from the literature to crosscheck the results.Then, a model based on previous efforts has been set up for computing the flow-field around the probe at high altitude.Finally the test case matrix has been computed and crosschecked with existing numerical predictions performed.Some possibilities of innovative magneto-hydrodynamic (MHD) technologies being applied to solve problems of re-entry vehicles heat protection are discussed in the fourth part.All presented data demonstrate necessity of further development of the radiative aerothermodynamics based on state-tostate approaches.
The usual full-field/scattered-field formulation is generalized to include a planar dielectric interface passing through the space. In this case, the source condition surrounding the central full-field region emits and captures waves consistent with scattering from a planar dielectric interface. Thus the wave in the outer scattered-field region represents just the part of the scattered wave that is due to non-planar dielectric or conductor geometry. The formulation is exact to machine precision, regardless of wavelength being smaller or larger than the simulation domain, and includes the exact second-order correction to the nominal scattering coefficients due to finite-difference truncation error. The method works even in the case of total internal reflection at the dielectric interface, that is, with the transmitted side exhibiting exponential decay rather than a propagating wave. A simple variation allows the dielectric to be a plasma, with correct scattering, regardless of whether the plasma is under-dense or over-dense. Possible applications for this facility range from RCS-type computations at hydrological or atmospheric interfaces, to geometry characterization or damage assessment of surfaces, to general boundary conditions for simulations of intermediate size EM phenomenon, e.g., L~ , to finally, an algorithm test-bed for the subject of cut-cell dielectric in the finite-difference representation.
Applying various stimuli to excite large-amplitude electrostatic structure within plasmas is a basic idea of plasma-based acceleration.However, because these stimuli are usually magnetized, whether or not their wakes within plasmas are purely electrostatic should be cautiously treated.By strict theory on self-consistent fields of charged particles, we make detailed investigations on the wakes of those magnetized stimuli and the acceleration by electromagnetic wakes.
Non-resonant, electron-impact, vibro-electronic excitation cross sections, involving vibrationally excited N 2 molecules, to the mixed valence-Rydberg b,c,o 1 Π u and ′ b , ′ c , ′ e 1 Σ u + singlet states are presented.These cross sections are calculated using the so-called similarity approach, accounting for the vibronic coupling among excited states, and compared with the experiments and different theoretical calculations.New cross sections for the electron-impact resonant vibrational excitation of CO 2 molecule are calculated, for the symmetric stretching mode, as a function of the incident electron energy and for the transitions (υ i ,0,0) → (υ f ,0,0) with υ i = 0,1,2 and for some selected value of υ f in the interval υ i ≤ υ f ≤ 10.A resonance potential curve and associated widths are calculated using the R-matrix method.Rate coefficients, calculated by assuming a Maxwellian electron energy distribution function, are also presented for the same (υ i ,0,0) → (υ f ,0,0) transitions.Electron-impact cross sections and rate coefficients for resonant vibrational excitations involving the diatomic species N 2 , NO, CO, O 2 and H 2 , for multi-quantic and mono-quantic transitions, are reviewed along with the cross sections and rates for the process of the dissociative electron attachment to H 2 molecule, involving a Rydberg excited resonant state of the ion.
This article presents an analytic investigation to calculate the width of the shock in pair plasma . A solitary elec- tromagnetic wave is propagated obliquely in the plasma where the wave direction is characterized by a propagation angle from direction of a background (constant) magnetic field . Based on Sagdeev method , the shock wave is determined by os- cillation of pseudo--particle in pseudo--potential well . It is shown that for any fixed value of the propagation angle , the width of the shock becomes an explicit function of Alfe'vn Mach number of plasma . Graphs of the width of the shock ver- sus Mach number represent a rapid montonous decreasing functions .
An experimental procedure to evaluate the dynamic yield strength of solids based on measuring the growth of the Richtmyer-Meshkov instability is proposed.To induce the Richtmyer-Meshkov instability in solids a shock is needed, so this technique is complementary to the one based on the Rayleigh-Taylor instability that is achieved by means of an isentropic compression.We have presented an analytical model elsewhere, validated against extensive finite element simulations, that describes the evolution of the Richtmyer-Meshkov instability in elastoplastic solids.The model shows that after reaching a maximum value, the time evolution of the perturbation at the solid interface remains oscillating.The maximum perturbation amplitude depends essentially on the yield strength of the material.The proposed technique needs only one experimental measurement that is related, through the scaling law given by the analytical model, to the yield strength of the material.
One of the most important advantages of particle simulation as compared to fluid simulation is the capacity for working with and tracing particles. In particle simulations, the test particle method is usually used to get some idea of the behavior of plasma or other substances. In this method, first, a small number of particles are injected into the frame of fixed electromagnetic fields. Then, movement of particles is investigated using the pattern of their electric fields. This method is useful; however, as we need to work with fixed fields in our system, it lacks precision. In this work, we adapted the particle simulations method, adding the flexibility of working with dynamic fields that come directly from the simulation. Here we have tried to investigate particle entry from the solar wind with northward Interpanetary Magnetic Filed (IMF) to the magnetospheric cusp. As our initial results shows, self consistent path of particles does not follow the magnetic field lines going to the cusp that is slightly in contrast to the conventional non self consistent results from test particle method.
We describe a particle advance algorithm for particle-in-cell simulation of highly magnetized charged particles that relaxes the time step constraint due to cyclotron motion.The method preserves the correct cyclotron radius for large time steps and corrects for magnetic field gradients without requiring explicit calculation of the particle magnetic moment.Application of the algorithm is illustrated with electron and ion single particle orbit calculations in a field reversed configuration with rotating magnetic fields.This technique is efficient and applicable to massively parallel simulation.
The aim of this work is to provide a relativistically correct characterization for the stability of counterstreaming plasma structures ubiquitous in fusion plasma experiments and astrophysical sources of nonthermal radiation.Here, in the first part of this work, a new relativistically correct approach is formulated for the counterstreaming plasmas in thermal equilibrium, on the basis of the relativistic Jüttner-Maxwell distribution function and a correct representation of this distribution in the laboratory frame of reference by using the appropriate Lorentz transformations for momentum and energy.The particle velocity resulting from the thermal motion and the bulk displacement of plasma particles is thus limited according to the relativistic theory to less than c (the speed of light in vacuum).New criteria are derived for the existence of counterstreams conditioned by the magnitude of their bulk velocity with respect to the thermal speed.Accurate simplified forms of the distribution functions derived here for different limits of the streaming velocity and the plasma temperature, will be invoked in the second part of this work as input to the stability analysis of these systems.
