Performance Portable Assembly For Plasma Fluid Equations.
Abstract not provided.
Bettencourt, Matthew Tyler↗
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Performance Portable Assembly For Plasma Fluid Equations.
Abstract not provided.
Bettencourt, Matthew Tyler↗
Parabola solitons for the nonautonomous KP equation in fluids and plasmas
Under investigation in this paper is a nonautonomous Kadomtsev–Petviashvili (KP) equation in fluids and plasmas. The integrability of this equation is examined via the Painlevé analysis and its multi-soliton solutions are constructed. A constraint is proposed to ensure the existence of parabola solitons for such KP equation. Based on the constructed solutions, the solitonic propagation and interaction, including the elastic interaction, inelastic interaction and soliton resonance for parabola solitons, are discussed. The results might be useful for shallow water wave and rogue wave.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
The B{sup −3/2} diffusion in magnetized plasma
Fluid equations with transport effects have been derived from summing up discrete particle effects in the configuration space. The diffusion coefficient takes a form different from, but equivalent to, the Kubo formula. By taking into account the decoherence along the field lines, the diffusive damping in the perpendicular direction, and the finite Larmor radius effect in the cyclotron resonance, it is shown that the diffusion of magnetized 3d plasma has a regime of B{sup −3/2} scaling which lies between the Bohm diffusion of B{sup −1} and the classical diffusion of B{sup −2}.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
High-order two-fluid plasma solver for direct numerical simulations of plasma flows with full transport phenomena
The two-fluid plasma equations for a single ion species, with full transport terms, including temperature and magnetic field dependent ion and electron viscous stresses and heat fluxes, frictional drag force, and ohmic heating terms, have been implemented in the CFDNS code and solved by using sixth-order non-dissipative compact finite differences for plasma flows in several different regimes. In order to be able to fully resolve all the dynamically relevant time and length scales, while maintaining computational feasibility, the assumptions of infinite speed of light and negligible electron inertia have been made. Non-dimensional analysis of the two-fluid plasma equations shows that, by varying the characteristic/background number density, length scale, temperature, and magnetic strength, the corresponding Hall, resistive, and ideal magnetohydrodynamic equations can be recovered as limiting cases. The accuracy and robustness of this two-fluid plasma solver in handling plasma flows in different regimes have been validated against four canonical problems: Alfven and whistler dispersion relations, electromagnetic plasma shock, and magnetic reconnection. For all test cases, by using physical dissipation and diffusion, with negligible numerical dissipation/diffusion, fully converged Direct Numerical Simulation (DNS)-like solutions are obtained when the ion Reynolds number based on the grid size is smaller than a threshold value which is about 2.3. For the magnetic reconnection problem, the results show that the magnetic flux saturation time and value converge when the ion and magnetic Reynolds numbers are large enough. Thus, the DNS-like results become relevant to practical problems with much larger Reynolds numbers.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
P24 Plasma Physics Summer School 2012 Los Alamos National Laboratory Summer lecture series for students [Slides]
This report covers the 2012 LANL summer lecture series for students. The lectures were: (1) Tom Intrator, P24 LANL: Kick off, Introduction - What is a plasma; (2) Bruno Bauer, Univ. Nevada-Reno: Derivation of plasma fluid equations; (3) Juan Fernandez, P24 LANL Overview of research being done in p-24; (4) Tom Intrator, P24 LANL: Intro to dynamo, reconnection, shocks; (5) Bill Daughton X-CP6 LANL: Intro to computational particle in cell methods; (6) Kirk Flippo, P24 LANL: High energy density plasmas; (7) Thom Weber, P24 LANL: Energy crisis, fission, fusion, non carbon fuel cycles; (8) Tom Awe, Sandia National Laboratory: Magneto Inertial Fusion; and (9) Yongho Kim, P24 LANL: Industrial technologies.
Astronomy & Astrophysics(79)↗
Model for a transformer-coupled toroidal plasma source
A two-dimensional fluid plasma model for a transformer-coupled toroidal plasma source is described. Ferrites are used in this device to improve the electromagnetic coupling between the primary coils carrying radio frequency (rf) current and a secondary plasma loop. Appropriate components of the Maxwell equations are solved to determine the electromagnetic fields and electron power deposition in the model. The effect of gas flow on species transport is also considered. The model is applied to 1 Torr Ar/NH{sub 3} plasma in this article. Rf electric field lines form a loop in the vacuum chamber and generate a plasma ring. Due to rapid dissociation of NH{sub 3}, NH{sub x}{sup +} ions are more prevalent near the gas inlet and Ar{sup +} ions are the dominant ions farther downstream. NH{sub 3} and its by-products rapidly dissociate into small fragments as the gas flows through the plasma. With increasing source power, NH{sub 3} dissociates more readily and NH{sub x}{sup +} ions are more tightly confined near the gas inlet. Gas flow rate significantly influences the plasma characteristics. With increasing gas flow rate, NH{sub 3} dissociation occurs farther from the gas inlet in regions with higher electron density. Consequently, more NH{sub 4}{sup +} ions are produced and dissociation by-products have higher concentrations near the outlet.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
The effect of dust charge variation, due to ion flow and electron depletion, on dust levitation
Using a fluid model, the plasma densities, electron temperature and ion Mach number in front of a powered electrode in different plasma discharges is computed. The dust charge is computed using OML theory for Maxwellian electrons and ions distributed according to a shifted-Maxwellian. By assuming force balance between gravity and the electrostatic force, the dust levitation height is obtained. The importance of the dust charge variation is investigated.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Novel approach to general curvilinear coordinates for plasma fluid applications
In general geometry, plasma fluid equations include nonlinear geometric sources associated with fictitious forces, which pose significant challenges to computer simulations. We reformulate the plasma fluid hierarchy to rigorously preserve geometry and conservation properties critical to numerical simulations, while concealing the geometric sources. In their discrete form, the reformulated models conserve mass, angular momentum, and energy naturally, by simple analogy with the continuum equations. These conservation properties have minimal requirements in discrete space, namely, the anti-symmetry of the first derivative and the orthogonality of the scalar and cross products. By decoupling magnetic geometry, coordinate systems, and numerical discretization, this enables maximum flexibility while preserving physics fidelity. As a testbed, we apply the novel representation to the resistive magnetohydrodynamic system, which involves a complete set of curvilinear operations. We verify the correctness of the approach using steady state liquid metal flows and the classic Orszag–Tang vortex.
Halpern, Federico D. [General Atomics, San Diego, ↗
Self-similar expansion of a warm dense plasma
The properties of an expanding plasma composed of degenerate electron fluid and non-degenerate ions are studied. For our purposes, we use fluid equations for ions together with the electron momentum equation that include quantum forces (e.g., the quantum statistical pressure, forces due to the electron-exchange and electron correlations effects) and the quasi-neutrality condition. The governing equation is written in a tractable form by using a self-similar transformation. Numerical results for typical beryllium plasma parameters revealed that, during the expansion, the ion acoustic speed decreases for both isothermal and adiabatic ion pressure. When compared with classical hydrodynamic plasma expansion model, the electrons and ions are found to initially escape faster in vacuum creating thus an intense electric field that accelerates most of the particles into the vacuum ahead of the plasma expansion. The relevancy of the present model to beryllium plasma produced by a femto-second laser is highlighted.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Experimental evidence of ion acoustic soliton chain formation and validation of nonlinear fluid theory
We perform one-dimensional fluid simulation of ion acoustic (IA) solitons propagating parallel to the magnetic field in electron-ion plasmas by assuming a large system length. To model the initial density perturbations (IDP), we employ a KdV soliton type solution. Our simulation demonstrates that the generation mechanism of IA solitons depends on the wavelength of the IDP. The short wavelength IDP evolve into two oppositely propagating identical IA solitons, whereas the long wavelength IDP develop into two indistinguishable chains of multiple IA solitons through a wave breaking process. The wave breaking occurs close to the time when electrostatic energy exceeds half of the kinetic energy of the electron fluid. The wave breaking amplitude and time of its initiation are found to be dependent on characteristics of the IDP. The strength of the IDP controls the number of IA solitons in the solitary chains. The speed, width, and amplitude of IA solitons estimated during their stable propagation in the simulation are in good agreement with the nonlinear fluid theory. This fluid simulation is the first to confirm the validity of the general nonlinear fluid theory, which is widely used in the study of solitary waves in laboratory and space plasmas.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Extended fluid models: Pressure tensor effects and equilibria
We consider the use of “extended fluid models” as a viable alternative to computationally demanding kinetic simulations in order to manage the global large scale evolution of a collisionless plasma while accounting for the main effects that come into play when spatial micro-scales of the order of the ion inertial scale d{sub i} and of the thermal ion Larmor radius ρ{sub i} are formed. We present an extended two-fluid model that retains finite Larmor radius (FLR) corrections to the ion pressure tensor while electron inertia terms and heat fluxes are neglected. Within this model we calculate analytic FLR plasma equilibria in the presence of a shear flow and elucidate the role of the magnetic field asymmetry. Using a Hybrid Vlasov code, we show that these analytic equilibria offer a significant improvement with respect to conventional magnetohydrodynamic shear-flow equilibria when initializing kinetic simulations.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
A primitive kinetic-fluid model for quasi-parallel propagating magnetohydrodynamic waves
The extension and limitation of the existing one-dimensional kinetic-fluid model (Vlasov-MHD (magnetohydrodynamic) model), which has been used to analyze parametric instabilities of parallel propagating Alfvén waves, are discussed. The inconsistency among the given velocity distribution functions in the past studies is resolved through the systematic derivation of the multi-dimensional Vlasov-MHD model. The linear dispersion analysis of the present model indicates that the collisionless damping of the slow modes is adequately evaluated in low beta plasmas, although the deviation between the present model and the full-Vlasov theory increases with increasing plasma beta and increasing propagation angle. This is because the transit-time damping is not correctly evaluated in the present model. It is also shown that the ponderomotive density fluctuations associated with the envelope-modulated quasi-parallel propagating Alfvén waves derived from the present model is not consistent with those derived from the other models such as the Landau-fluid model, except for low beta plasmas. The result indicates the present model would be useful to understand the linear and nonlinear development of the Alfvénic turbulence in the inner heliosphere, whose condition is relatively low beta, while the existing model and the present model are insufficient to discuss the parametric instabilities of Alfvén waves in high beta plasmas and the obliquely propagating waves.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Premixed Combustion Simulations with a Self-Consistent Plasma Model for Initiation
Combustion simulations of H2-O2 ignition are presented here, with a self-consistent plasma fluid model for ignition initiation. The plasma fluid equations for a nanosecond pulsed discharge are solved and coupled with the governing equations of combustion. The discharge operates with the propagation of cathode directed streamer, with radical species produced at streamer heads. These radical species play an important role in the ignition process. The streamer propagation speeds and radical production rates were found to be sensitive to gas temperature and fuel-oxidizer equivalence ratio. The oxygen radical production rates strongly depend on equivalence ratio and subsequently results in faster ignition of leaner mixtures.
97 MATHEMATICS AND COMPUTING↗
Hybrid equilibria of field-reversed configurations
This paper presents the first detailed model of hybrid equilibria relevant to field-reversed configuration experiments, leading to a system of equations that are solved for a range of fully two-dimensional equilibria. Several features of these highly kinetic objects are explored. The range of equilibria is primarily dependent on a single free parameter related to the flow shear. The level of flow shear has a profound effect on the structure, especially near the separatrix. This likely has a strong influence on both stability and transport properties. Higher flow shear is favorable in every respect. The key factor behind the influence of flow shear is the relatively rapid end loss of unconfined ions. Differences between hybrid and static-fluid equilibrium models are highlighted, including the integrity of surface functions, the effect of flow shear, and the scrape-off layer thickness.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
An asymptotic preserving automatic domain decomposition method for the Vlasov–Poisson–BGK system with applications to plasmas
In this work we present an efficient strategy to deal with plasma physics simulations in which localized departures from thermodynamical equilibrium are present. The method is based on the introduction of intermediate regions which allows smooth transitions between kinetic and fluid zones. In this paper we extend Domain Decomposition techniques, obtained through dynamic coupling and buffer zones, to the study of plasmas and, moreover, we combine them with Asymptotic Preserving and Asymptotically Accurate strategies for the time integration. We use a hybrid scheme in which both kinetic and fluid descriptions are considered and coupled together while the kinetic model is solved by asymptotic preserving and accurate methods, in order to guarantee high efficiency and accuracy in all regimes. The numerical scheme is validated and its performances are analyzed by numerical simulations.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
1-D fluid model of atmospheric-pressure rf He+O{sub 2} cold plasmas: Parametric study and critical evaluation
In this paper atmospheric-pressure rf He+O{sub 2} cold plasmas are studied by means of a 1-D fluid model. 17 species and 60 key reactions selected from a study of 250+ reactions are incorporated in the model. O{sub 2}{sup +}, O{sub 3}{sup -}, and O are the dominant positive ion, negative ion, and reactive oxygen species, respectively. Ground state O is mainly generated by electron induced reactions and quenching of atomic and molecular oxygen metastables, while three-body reactions leading to the formation of O{sub 2} and O{sub 3} are the main mechanisms responsible for O destruction. The fraction of input power dissipated by ions is {approx}20%. For the conditions considered in the study {approx}6% of the input power is coupled to ions in the bulk and this amount will increase with increasing electronegativity. Radial and electrode losses of neutral species are in most cases negligible when compared to gas phase processes as these losses are diffusion limited due to the large collisionality of the plasma. The electrode loss rate of neutral species is found to be nearly independent of the surface adsorption probability p for p > 0.001 and therefore plasma dosage can be quantified even if p is not known precisely.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
The recovery of glow-plasma structure in atmospheric radio frequency microplasmas at very small gaps
In atmospheric radio frequency discharges at 13.56 MHz, with the electrode gap reduced, the sheath region eventually occupies a main portion of the electrode spacing and the bulk plasma region is significantly compressed. The computational results in this letter based on a one-dimensional fluid model show that by increasing the excitation frequency over 13.56 MHz, the traditional glow-plasma structure could gradually recover even at very small sizes with a well defined quasineutral plasma region, and the electron density is improved but the electric fields in sheath region are reduced. This study indicates that the excitation frequency can be used to modulate the discharge structure and then tailor the plasma-surface interaction in atmospheric microplasmas.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗