Two-temperature Hydrodynamic Model Research Articles

Динамика и неравновесный ионный состав плазмы многозарядных ионов, создаваемой при взаимодействии мощного импульса лазерного излучения с цилиндрической плазменной мишенью

Based on the numerical simulation results in the framework of a nonstationary one-dimensional (1D) two-temperature (2T) radiative hydrodynamic (RHD) model, the main physical processes that determine the formation of cylindrical plasma bunches with a non-equilibrium charge containing high ionized ions at laser intensity QL≤10^14 W/cm^2 and energy EL~10 J/cm are analyzed. The results of the work are devoted to the creation of active media for lasers generating in the extreme ultraviolet (EUV) and soft X-ray (SXR) spectral ranges.

Research and modeling of laser ablation by ultra-short laser pulses for metal targets

In this article a new mathematical model for a laser metal ablation by ultra-short duration laser pulses is proposed. The computational process is based on a two-temperature hydrodynamic model for electrons and ions. Some improvements are made and wide-range equation of state for metals is included in model. The results of the computer simulation of ablation depth for aluminum and copper are compared with experimental data at a different laser fluency values. We obtained a good agreement between the experimental and calculated data on the ablation depth.

Simulation of multi-pulse laser ablation for laser-induced breakdown spectroscopy applications

Using a two-temperature hydrodynamic model, we analyze the regimes of multi-pulse laser ablation of aluminum by focusing on long-term plasma plume parameters. It is demonstrated that the plasma luminosity in single-, double- and multi-pulse ablation regimes may vary by two orders of magnitude. We also show that the double-pulse ablation regime with 5 J/ $$\hbox {cm}^2$$ fluence of each pulse and 100-ps inter-pulse delay is the most effective case giving rise to 250 times increase of the plasma brightness with respect to a single-pulse ablation regime with the same incident energy.

Beyond equilibrium thermodynamics in the low temperature plasma processor

Low temperature plasmas are open driven thermodynamic systems capable of increasing the free energy of the mass that flows through them. An interesting thing about low temperature plasmas is that different species have different temperatures at the same location in space. Since thermal equilibrium cannot be assumed, many of the familiar results of equilibrium thermodynamics cannot be applied in their familiar form to predict, e.g., the direction of a chemical reaction. From the perspective of classical processing governed by thermal equilibrium, examples of highly unexpected gas-phase chemical reactions (CO2 dissociation, NO, N2H4, O3 synthesis) and solid material transformations (surface activation, size-focusing, and hyperdoping) promoted by low temperature plasmas are presented. The lack of a known chemical reaction equilibrium criterion prevents assessment of predictive kinetics models of low temperature plasmas, to ensure that they comply with the laws of thermodynamics. There is a need for a general method to predict chemical reaction equilibrium in low temperature plasmas or an alternative method to establish the thermodynamic admissibility of a proposed kinetics model. Toward those ends, two ideas are explored in this work. The first idea is that chemical reactions in low temperature plasmas proceed toward a thermal equilibrium state at an effective temperature intermediate between the neutral gas temperature and the electron temperature. The effective temperature hypothesis is simple, and surprisingly is adequate for elucidation in some systems, but it lacks generality. The general equation for nonequilibrium reversible–irreversible coupling (GENERIC) is a general beyond equilibrium thermodynamics framework that can be used to rigorously establish the thermodynamic admissibility of a set of dynamic modeling equations, such as a kinetic model, without knowledge of the final state that the system is tending toward. The use of GENERIC is described by way of example using a two-temperature hydrodynamic model from the literature. The conclusion of the GENERIC analysis presented in this work is that the concept of superlocal equilibrium is thermodynamically admissible and may be applied to describe low temperature plasmas, provided that appropriate terms are included for exchange of internal energy and momentum between different species that may have different temperatures and bulk velocities at the same location in space. The concept of superlocal equilibrium is expected to be of utility in future work focused on deriving equilibrium criteria for low temperature plasmas.

Equation of state for computer simulation of metal ablation by femtosecond laser pulses

In this paper a wide-range equation of state for computer simulation of metal ablation by femtosecond laser pulses is proposed. The simulation results are compared with experimental data for several metals (Al, Au, Cu, Ni). A good agreement for numerical results with experimental data shows that this equation of state together with two-temperature hydrodynamic model can be employed for choosing laser parameters to receive better accuracy in simulation of metal ablation.

Hydrodynamic modeling of hot-carrier effects in a PN junction solar cell

This article presents a one-dimensional two-temperature hydrodynamic model to study the thermal and electrical behavior of a gallium arsenide (GaAs) PN junction solar cell. This model treats both electron and heat transfer on equal footing and includes Gauss’s law, continuity and momentum equations for electrons and holes, and energy balance using temperature for both carriers and lattice. A zero-order system of equations is obtained using asymptotic series expansions based on the electron Reynolds number for steady-state conditions. An iterative scheme is implemented to solve the zero-order system. The results show the influence of carriers and lattice temperatures in the electrical performance of a GaAs PN junction solar cell. Higher values of power output are obtained with low lattice temperature and hot energy carriers. This modeling contributes to improve the thermal control in photovoltaic technologies.

Electron acceleration at grazing incidence of a subpicosecond intense laser pulse onto a plane solid target

AbstractGeneration of hot electrons at grazing incidence of a subpicosecond relativistic-intense laser pulse onto a plane solid target is analyzed for the parameters of petawatt class laser systems. We study preplasma formation on the surface of solid aluminum targets produced by laser prepulses with a different time structure. For modeling of the preplasma dynamics, we use a wide-range two-temperature hydrodynamic model. As a result of simulations, the preplasma expansion under the action of the laser prepulse and the plasma density profiles for different contrast ratios of the nanosecond pedestal are found. These density profiles are used as the initial density distributions in three-dimensional particle-in-cell simulations of electron acceleration by the main P-polarized laser pulse. Results of modeling demonstrate a substantial increase of the characteristic energy and number of accelerated electrons for the grazing incidence of a subpicosecond intense laser pulse in comparison with the ponderomotive scaling of laser–target interaction.

Laser electron acceleration in the prepulse produced plasma corona

The generation of hot electrons at grazing incidence of a subpicosecond relativistic-intense laser pulse onto the plane solid target is analyzed for the parameters of the petawatt class laser systems. We study the preplasma formation on the surface of solid Al target produced by the laser prepulses with different time structure. For modeling of the preplasma dynamics we use a wide-range two-temperature hydrodynamic model. As a result of simulations, the preplasma expansion under the action of the laser prepulse and the plasma density profiles for different contrast ratios of the nanosecond pedestal are found. These density profiles were used as the initial density distributions in 3-D PIC simulations of electron acceleration by the main P-polarized laser pulse. Results of modeling demonstrate the substantial increase of the characteristic energy and number of accelerated electrons for the grazing incidence of a subpicosecond intense laser pulse in comparison with the laser-target interaction at normal incidence.

Collision of plane thermonuclear detonation waves in a preliminarily compressed DT mixture

The paper deals with a one-dimensional problem on symmetric irradiation of a plane DT fuel layer with a thickness 2H and density ρ0 ⩽ 100ρs (where ρs is the density of the DT fuel in the solid state at atmospheric pressure and a temperature of 4 K) by two identical monoenergetic proton beams with a kinetic energy of 1 MeV, an intensity of 1019 W/cm2, and a duration of 50 ps. The problem is solved in the framework of one-fluid two-temperature hydrodynamic model that takes into account the equation of state for hydrogen, electron and ion heat conductivities, kinetics of the DT reaction, plasma self-radiation, and plasma heating by α-particles. The irradiation of the fuel results in the appearance of two counterpropagating detonation waves to the fronts of which rarefaction waves are adjacent. The efficiency of the DT reaction after the collision (reflection from the plane of symmetry) of the detonation waves depends on the spatial homogeneity of thermodynamic functions between the fronts of the reflected detonation waves. At Hρ0 ≈ 1 g/cm2, the gain factor is G ≈ 200, whereas at Hρ0 ≈ 5 g/cm2, it is G > 2000. As applied to a cylindrical target that is ignited from ends and in which the cylinder with the fuel is surrounded by a heavy magnetized shell, the obtained values of the burn-up and gain factors are maximum possible. To estimate the ignition energy Eig of a cylindrical target by using solutions to the one-dimensional problem, a quasi-one-dimensional model is developed. The model assumes that the main mechanism of target ignition is fuel heating by α-particles. The trajectories of α-particles are limited by a cylindrical surface with a given radius, which is a parameter of the model and is identified with the fuel radius in the target and the radii of the irradiating proton beams. This model reproduces the well-known theoretical dependence Eig ∼ ρ0−2 and yields Eig = 160 kJ as a lower estimate of the ignition energy for ρ0 = 100ρs ≈ 22 g/cm3.

Thermal influence on charge carrier transport in solar cells based on GaAs PN junctions

The electron and hole one-dimensional transport in a solar cell based on a Gallium Arsenide (GaAs) PN junction and its dependency with electron and lattice temperatures are studied here. Electrons and heat transport are treated on an equal footing, and a cell operating at high temperatures using concentrators is considered. The equations of a two-temperature hydrodynamic model are written in terms of asymptotic expansions for the dependent variables with the electron Reynolds number as a perturbation parameter. The dependency of the electron and hole densities through the junction with the temperature is analyzed solving the steady-state model at low Reynolds numbers. Lattice temperature distribution throughout the device is obtained considering the change of kinetic energy of electrons due to interactions with the lattice and heat absorbed from sunlight. In terms of performance, higher values of power output are obtained with low lattice temperature and hot energy carriers. This modeling contributes to improve the design of heat exchange devices and thermal management strategies in photovoltaic technologies.

A plasma jet produced in a segmented plasmatron: modelling and experiment

Nitrogen and argon plasmas with a small admixture of air produced in a segmented plasmatron are studied both experimentally and theoretically. A two-temperature hydrodynamic model is used to simulate the plasma flow inside the plasmatron. The calculated plasma temperature and electron density are in reasonable agreement with the experimental values obtained from emission spectroscopy. The electron temperatures are several thousand kelvins higher than the atom temperatures, showing that the plasmas produced in the segmented plasmatron are in non-equilibrium.

Electron‐Ion Relaxation, Phase Transitions, and Surface Nano‐Structuring Produced by Ultrashort Laser Pulses in Metals

AbstractFundamental physical phenomena in metals irradiated by ultrashort laser pulses with absorbed fluences higher than few tens of mJ/cm2 are investigated. For those fluences, laser‐produced electron distribution function relaxes to equilibrium Fermi distribution with electron temperature Te within a short time of 10‐100 fs. Because the electron subsystem has Te highly exceeding much the ion subsystem temperature Ti the well‐known twotemperature hydrodynamic model (2T‐HD) is used to evaluate heat propagation associated with hot conductive electron diffusion and electron‐ion energy exchange. The model coefficients of electron heat conductivity κ (ϱ, Te, Ti) and electron‐ion coupling parameter α (ϱ, Te) together with 2T equation of state E (ϱ, Te, Ti) and P (ϱ, Te, Ti) are calculated.Modeling with 2T‐HD code shows transition of electron heat wave from supersonic to subsonic regime of prop‐agation. At the moment of transition the heat wave emits a compression wave moving into the bulk of met al. Nonlinear evolution of the compression wave after its separation from the subsonic heat wave till spallation of rear‐side layer of a film is traced in both 2T‐HD modeling and molecular dynamics (MD) simulation.For fluences above some threshold the nucleation of voids in frontal surface layer is initiated by strong tensile wave following the compression wave. If the absorbed fluence is ∼30 % above the ablation threshold than void nucleation develops quickly to heavily foam the molten met al. Long‐term evolution of the metal foam including foam breaking and freezing is simulated. It is shown that surface nano‐structures observed in experiments are produced by very fast cooling of surface molten layer followed by recrystallization of supercooled liquid in disintegrating foam having complex geometry. Characteristic lengths of such surface nanostructures, including frozen pikes and bubbles, are of the order of thickness of molten layer formed right after laser irradiation. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Theoretical investigation of the decay of an SF6 gas-blast arc using a two-temperature hydrodynamic model

The behaviour of a decaying SF6 arc, which is representative of the approach to the final current-zero state of switching arcs in a high-voltage circuit breaker, is theoretically investigated by a two-temperature hydrodynamic model, taking into account the possible departure of the plasma state from local thermodynamic equilibrium (LTE). The model couples the plasma flow with electromagnetic fields in a self-consistent manner. The electrons and heavy species are assumed to have different temperatures. The species composition, thermodynamic properties and transport coefficients of the plasma under non-LTE conditions are calculated from fundamental theory. The model is then applied to a two-dimensional axisymmetric SF6 arc burning in a supersonic nozzle under well-controlled conditions; for this configuration, experimental results are available for comparison. The effect of turbulence is considered using the Prandtl mixing-length model. The edge absorption of the radiation emitted by the arc core is taken into account by a modified net emission coefficient approach. The complete set of conservation equations is discretized and solved using the finite volume method. The evolution of electron and heavy-particle temperatures and the total arc resistance, along with other physical quantities, is carefully analysed and compared with those of the LTE case. It is demonstrated that the electron and heavy-particle temperature diverge at all times in the plasma–cold-flow interaction region, in which strong gas flow exists, and further in the transient current-zero period, in which case the collision energy exchange is ineffective. This study quantitatively analyses the energy exchange mechanisms between electrons and heavy particles in the high-pressure supersonic SF6 arcs and provides the foundation for further theoretical investigation of transient SF6 arc behaviour as the current ramps down to zero in gas-blast circuit breakers.

Dynamics of thin metal foils irradiated by moderate-contrast high-intensity laser beams

Laser contrast is a crucial parameter in experiments with high-intensity high-energy pulses. For relativistic intensities of the main pulse ≳1019W/cm2, even high-contrast beams can produce plasma on the target surface due to a long nanosecond prepulse action which results in an undesirable early smearing of the target. In particular, dynamics of thin foils under the prepulse action is especially important for the laser ion acceleration technique and x-rays generation. To avoid the influence of the long laser prepulse, a thin foil can be arranged in front of the target. The analysis of the multi-stage foil dynamics is performed using a wide-range two-temperature hydrodynamic model, which correctly describes the foil expansion starting from the normal solid density at room temperature. Simulations show that varying the foil thickness, one can diminish the prepulse transmission through the foil material in many orders of magnitude and at the same time provide the total transparency of the foil plasma by the moment of the main high-intensity ultra-short pulse arrival. Modeling of shielded and unshielded target dynamics demonstrates the effectiveness of this technique. However, the prepulse energy re-emission by the shielding foil plasma can be sizable producing an undesirable early heating of the target placed behind the foil.

Temperature influence on hydrodynamic instabilities in a one-dimensional electron flow in semiconductors

Hydrodynamic instabilities in one-dimensional electron flow in semiconductor and their dependency with the electron and lattice temperatures are studied here. The driving force for the electrons is imposed by a voltage difference, and the hydrodynamic and electrostatic equations are linearized with respect to the steady-flow solution. A two-temperature hydrodynamic model predicts a stable electron flow through the semiconductor. A one-temperature hydrodynamic model is obtained by neglecting the electron energy losses due to heat conduction and scattering. This model shows that the electron flow can become unstable and establishes a criterion for that. Applied voltage and temperature can play the role of tunable parameters in the stability of the electron flow.

MHD simulation of high-current subsonic vacuum arc under different distributed axial magnetic fields

Based on two-temperature magnetic hydrodynamic (MHD) model, the influence of saddle-shaped distributed axial magnetic field (AMF, linearly increases along radial position) and bell-shaped distributed AMF (linearly decreases along radial position) on plasma loss and heat flux density to anode in subsonic high-current vacuum arc (HCVA) is simulated and analyzed. According to the simulation results, the saddle-shaped AMF can more effectively inhibit plasma loss from arc column than that of bell-shaped AMF. Comparisons between simulation results and experimental results further verify the correctness of model and simulation.

Effect of a near-cathode sheath on heat transfer in high-pressure arc plasmas

Numerical simulation of a high-pressure arc discharge has been performed with a self-consistent modelling of most of the components, including the electrodes, and the interactions between them. In particular, the arc column and the cathodic part of the discharge are simulated by means of a two-temperature hydrodynamic model and of a model of nonlinear surface heating, respectively. Simulation results are given for a free-burning arc in atmospheric-pressure argon in the range of arc currents from 10 to 200 A. It is found that the electric power deposited into the near-cathode layer is transported not only to the cathode but also to the arc column, an effect that cannot be described by the local thermodynamic equilibrium (LTE) model. The electron enthalpy transport substantially exceeds the net contribution of thermal conduction by the electrons and heavy particles and is thus the dominating mechanism of energy transfer from the near-cathode layer to the arc column. The predicted gas temperatures along the arc axis in the arc column using the LTE model are much higher than the calculated electron and heavy-particle temperatures (∼1000–2000 K or higher) under the same operation conditions using the non-equilibrium model with the consideration of the near-cathode sheath for the cases studied in the present paper. Studies on the influences of the cathode shapes and metal vapour contaminations on the arc characteristics will be conducted in future work.

Structure of the fronts of strong collisional shock waves in an ideal two-temperature electron-ion plasma with ions of arbitrary charge

Solutions in the form of plane running waves are investigated numerically in the framework of a two-temperature hydrodynamic model of a fully ionized ideal plasma with ions of arbitrary charge number Z0. Most simulations were carried out for simple boundary conditions corresponding to a cold immobile plasma at the front of a running wave. All the solutions obtained have a discontinuity in the form of an isoelectronic-thermal jump, whose parameters relax to their steady-state values in the course of calculation. The problem of finding numerical solutions in which all the quantities at infinity take on finite (equilibrium) values actually reduces to the problem of the front structure of a strong shock wave. For a plasma with singly changed ions (Z0 = 1), numerical solutions were found to coincide with the previously known solution. For a plasma with arbitrarily charged ions (Z0 > 1), numerical solutions were obtained for the first time on the basis of justified formulas for the electron thermal conductivity.

Decay and post-arc phases of a SF6 arc plasma: a thermal and chemicalnon-equilibrium model

After current zero in a high-voltage SF6 circuit breaker, therecovery voltage heats the remaining electrons, producing departures fromthermal equilibrium that may modify the electrical conductivity of the mediumand thus the interruption capability of the apparatus. In this study wepresent a two-temperature hydrodynamic model coupled with a kinetic model,applied to the extinction of a blown SF6 arc in a two-dimensional simplifiedgeometry. The free decay and the post-arc phase with the recovery voltage havebeen studied. The kinetic part of the modelling allows us to calculate theevolution of the electron number density. A simplified turbulence model hasbeen added to study its influence on the post-arc phase.The main results ofthis study reinforce the conclusions obtained taking into account only thechemical non-equilibrium: the departures from equilibrium tend to decrease theinterruption capability predicted by the model. This effect is due to the weakenergy exchange by elastic collisions between the electrons and the heavyparticles, leading to an electron temperature higher than the gas temperaturewhich favours the ionization of the medium submitted to a recovery voltage.

X-ray and pressure conditions on the first wall of a particle-beam inertial-confinement reactor

Because of the presence of a chamber gas in a particle-beam reactor cavity, non-neutron target debris created from thermonuclear burn will be modified or stopped before it reaches the first reactor wall.The resulting modified spectra and pulse lengths and the cavity overpressure created by the momentum and energy exchange between the debris and gas need to be calculated to determine their effect on the first wall.The purpose of this paper is to present results of the debris-background-gas problem obtained with a one-fluid,two-temperature plasma hydrodynamic computer code model which includes multi-frequency radiation transport.Spherical symmetry, ideal-gas equation-of-state, and LTE for each radiation frequency group were assumed.The transport of debris ions was not included, and all the debris energy was assumed to be in radiation. The calculated X-ray spectra and pulse lengths and the background overpressure are presented. The impact of the initial target spectra on these chamber conditions is discussed.