Plasma Expansion In Vacuum Research Articles

Recombination Processes of Multi-Charge Ions of a Laser Plasma

The presence of an obstacle on the path of laser plasma expansion in vacuum leads to an increase in the ion charge multiplicity, an expansion of the energy spectrum, and an increase in the total number of ions. The peculiarities of the interaction with a solid-state obstacle are largely associated with the appearance of a shock wave in it, which affects the course of recombination processes. It is shown that it is possible to control the parameters of a recombining laser plasma by changing the expansion dynamics at later stages using solid-state obstacles.

Grid coupling mechanism in the semi-implicit adaptive Multi-Level Multi-Domain method

The Multi-Level Multi-Domain (MLMD) method is a semi-implicit adaptive method for Particle-In-Cell plasma simulations. It has been demonstrated in the past in simulations of Maxwellian plasmas, electrostatic and electromagnetic instabilities, plasma expansion in vacuum, magnetic reconnection [1, 2, 3]. In multiple occasions, it has been commented on the coupling between the coarse and the refined grid solutions. The coupling mechanism itself, however, has never been explored in depth. Here, we investigate the theoretical bases of grid coupling in the MLMD system. We obtain an evolution law for the electric field solution in the overlap area of the MLMD system which highlights a dependance on the densities and currents from both the coarse and the refined grid, rather than from the coarse grid alone: grid coupling is obtained via densities and currents.

Numerical simulations of stable explosive-emission center plasma expansion in vacuum

We present the results of our numerical simulations of the stable cathode-flare expansion stage in the vacuum-breakdown switching period. We used the model of two-fluid hydrodynamics with corrections that allowed it to be applied to a consistent description of the electron and ion transport in plasma and the electron transport in a plasma-anode vacuum gap without imposing any joining conditions at the expanding plasma boundary. We have analyzed the dynamics of the density, directed velocity, and temperature profiles for both components and the influence of various factors on the plasma-cloud expansion velocity.

Multi-level multi-domain algorithm implementation for two-dimensional multiscale particle in cell simulations

There are a number of modeling challenges posed by space weather simulations. Most of them arise from the multiscale and multiphysics aspects of the problem. The multiple scales dramatically increase the requirements, in terms of computational resources, because of the need of performing large scale simulations with the proper small-scales resolution. Lately, several suggestions have been made to overcome this difficulty by using various refinement methods which consist in splitting the domain into regions of different resolutions separated by well defined interfaces. The multiphysics issues are generally treated in a similar way: interfaces separate the regions where different equations are solved.This paper presents an innovative approach based on the coexistence of several levels of description, which differ by their resolutions or, potentially, by their physics. Instead of interacting through interfaces, these levels are entirely simulated and are interlocked over the complete extension of the overlap area. This scheme has been applied to a parallelized, two-dimensional, Implicit Moment Method Particle in Cell code in order to investigate its multiscale description capabilities. Simulations of magnetic reconnection and plasma expansion in vacuum are presented and possible implementation options for this scheme on very large systems are also discussed.

Characterization of 1064 nm Nd:YAG laser-produced cu plasma

The plasma was produced by focusing Nd:YAG laser pulses of 1064 nm wavelength on to a copper target at laser fluences of 5.35, 6.95, and 9.33 J/cm2. An ion collector placed along the target surface normal was used to record the time-of-flight (TOF) ion signal during plasma expansion in vacuum. The TOF ion pulses were deconvoluted using the Coulomb-Boltzmann-shifted function to estimate the available Cu ion charge states, equivalent plasma ion temperature, and accelerating potential in the nonequilibrium plasma. The maximum available ion charge state, equivalent plasma ion temperature, and accelerating potential are found to increase with laser fluence. In the local thermal equilibrium conditions, the accelerating potential can be supposed to apply across a distance of the order of the Debye length. The Debye length and, hence, the electric field in the laser produced plasma at three laser fluences values were estimated. The electric field was in the range of 1 MV/cm and increased with laser fluence. In the laser fluence range used in this work, the sum of thermal and adiabatic energy of the ion was slightly higher than its Coulomb energy.

Angular distributions of flux and energy of the ions emitted during pulsed laser ablation of copper

An experimental study on the pulsed laser ablation of copper by using Nd-YAG laser radiation of 1064 nm wavelength at a fluence of 13 J/cm2 is reported. A time-resolving plane Langmuir probe, placed at various angles with respect to the target surface normal, is used to record temporal variation of ion currents during the plasma expansion in vacuum. The measured angular distributions of integrated ion yields are strongly peaked in forward direction. The experimentally determined plume expansion coefficient Zinf/Xinf = 2.1±0.2 is in good agreement with the previous studies. Time-of-flight measurements indicated that the energy of various ion components is highest along target surface normal and decreases with increase of the angle, however the effect of angle is more pronounced on the faster ions. The energy spread of the ions decreases approximately from ±670 eV to ±19 eV as the probe angle increases from 0° to 60°. The measured angular dependence of ion yield and most probable ion energy nicely follows the trends predicted by Anisimov's plume expansion model.

Langmuir Probe Measurements of Nd-YAG Laser-Produced Copper Plasmas

The plasma was produced by focusing Nd-YAG laser pulses of 1064-nm wavelength and 10-ns duration onto a copper target. A time-resolving plane Langmuir probe was used to record the electron and ion currents during the plasma expansion in vacuum. The Langmuir probe theory was used to determine the temporal variation of the plasma potential, electron temperature, and ion density. At the time of maximum ion current, the estimated plasma potential, electron temperature, and ion density were 2.42 V, 3.28 eV, and 2.30 × 1012 cm-3, respectively. In addition, a time-of-flight signal was used to determine the ion density and velocity of the various ion components as a function of laser irradiance and probe angle w.r.t. target surface normal. For the range of laser irradiance, 4-13 × 108 W/cm2, we found an ion density in the range of 6.88 × 1010-2.64 × 1012 cm-3 and an ion velocity in the range of 2.2-4.6 × 106 cm s-1 at the time of maximum ion current. In particular, the velocity of the fastest plume component was most affected by the irradiance. The estimated threshold irradiance for the onset of plasma was 3.95 × 108 W/cm2. The experimental scaling laws for the variation of ion velocity and ion charge with the laser irradiance and probe angle were proposed.

Investigation of laser-produced aluminum plasma

Abstract At DMFCI of Catania University, where a Quanta System Nd:YAG laser 600 mJ of energy, 1064 nm wavelength and 6 ns pulse length operates, experiments about plasma expansion in vacuum (

Data elaboration of proton beams produced by high-energy laser-generated plasmas

The proton beam production from high-energy laser-generated plasma is increasingly becoming of special interest for investigations in the field of new techniques of ion acceleration, nuclear physics, astrophysics and radiotherapy. The evolution of short-pulsed lasers, from the nanosecond to the femtosecond pulse scale, has allowed for an increase in intensity from about 1010 W/cm2 to about 1020 W/cm2 with a consequent increase of the kinetic energy of the plasma-generated ions. Thus proton energy has increased from about 100 eV at low intensity to about 100 MeV at the actual femtosecond-terawatt lasers. Although the emitted ions are multi-energetic, the use of thin hydrogenated targets and a high repetition rate can be employed to obtain high proton energy, narrow energy spread, high ion directivity and high current. Literature data indicate that the proton energy, the equivalent plasma temperature and the Coulomb acceleration increase with the pulse intensity. The use of femtosecond-terawatt lasers may produce very intense electric fields in the non-equilibrium plasma, which accelerate ions up to tens of MeV/amu. Ponderomotive forces, supersonic plasma expansion in vacuum, self-focusing effects and the high plasma temperature influence the ion plasma acceleration. Literature data can be fitted by Coulomb–Boltzmann-shifted functions which permit a separation of the thermal contribution from the Coulomb one. The latter increases at very high laser intensities to a greater extent than its thermal counterpart.

Laser induced fluorescence of the ferroelectric plasma source assisted hollow anode discharge

Parameters of the plasma produced by a ferroelectric plasma source (FPS) assisted high-current (∼1 kA), hollow anode (HA), low-pressure (10−4 Torr) Ar gas discharge were studied using a time- and space-resolved laser induced fluorescence (LIF) diagnostic technique. It was shown that the plasma filling of the HA cavity occurs due to the expansion of the plasma flows generated by the FPSs with a gradual time-dependent increase in the plasma density along the length of the HA cavity. These data were verified by the results of one-dimensional modeling of the plasma expansion in vacuum and time-dependent collisional-radiative modeling. Also, LIF diagnostics, which was tested on the saturation effect both experimentally and numerically, showed that the plasma ion temperature gradually increases during the discharge reaching ∼9 eV at its end. Various phenomena (plasma kinetic instabilities, charge-exchange processes during the plasma ion interaction with the HA walls, and the model of neutral atoms ionization in...

Characterization of a controlled plasma expansion in vacuum for laser driven ion acceleration

We present experimental and numerical results on the formation of a controlled plasma density gradient in front of a solid target irradiated with a subpicosecond, moderate intensity laser pulse. Interferometry with femtosecond probe is used to map the temporal evolution of the spatial density distribution of the generated plasma. Experimental results are found to be in good agreement with 1D1/2 hydrodynamic simulations. Moreover, these numerical simulations enable us to determine the impact of such a heating beam on the target rear surface and to correlate the plasma gradient that can be produced on the illuminated surface with the position of the shock wave in the bulk.

A volume of fluid method for a two-dimensional plasma expansion problem

This paper is devoted to the numerical study of a two-dimensional model for plasma expansion in vacuum. The plasma, constituted of ions and electrons, is injected from a part of the cathode and undergoes a thermal expansion. Due to the positive anode potential, electrons are emitted from the plasma–vacuum interface, forming an electron beam. Moreover, electron emission produces a reaction-pressure force which slows down the plasma expansion. Previous works [P. Degond, C. Parzani, M.H. Vignal, Un modéle d’expansion de plasma dans le vide, C. R. Acad. Sci. Paris 335 (2002) 399; P. Degond, C. Parzani, M.H. Vignal, Plasma expansion in vacuum: modeling the breakdown of quasineutrality, SIAM, Multiscale Model. Simul. 2 (2003) 158; P. Degond, C. Parzani, M. H. Vignal, A model for plasma expansion in the vacuum, in: Proceedings of the Conference “Free Boundary Problems 2002”, Trento, June 2002] have been realized to describe this process in the one-dimensional case. One of the main goal is to get a precise description of the interface motion. The aim of the present work is to explore more realistic cases investigating a two-dimensional model. However, considering upper dimensions yields to new difficulties essentially from a numerical point of view. Indeed, in the 2D space case, the plasma–vacuum interface is no more a point but a curve. Therefore, in this work, after proposing a two-dimensional model, we focus on the interface tracking using a volume of fluid method. We perform numerical simulations on two test cases. The first test case consists in a two-dimensional fluid compression for which an analytic solution is known. The second test case is the plasma bubble expansion between two electrodes.

An asymptotic preserving scheme for the two-fluid Euler–Poisson model in the quasineutral limit

This paper deals with the modeling of a plasma in the quasineutral limit using the two-fluid Euler–Poisson system. In this limit, explicit numerical schemes suffer from severe numerical constraints related to the small Debye length and large plasma frequency. Here, we propose an implicit scheme which reduces to a scheme for the quasineutral Euler model in the quasineutral limit. Such a property is referred to as “asymptotic preservation”. One of the distinctive features of this scheme is that it has a comparable numerical cost to that of an explicit scheme: simply the Poisson equation is replaced by a different (but formally equivalent) elliptic problem. We present numerical simulations for two different one-dimensional test-cases. They confirm the expected stability of the scheme in the quasineutral limit. They also show that this scheme has some accuracy problems in the limit of small electron to ion mass ratio in reproducing the correct electron velocity. But this problem is already present in the results of the classical algorithm. Numerical simulations are also performed for a two-dimensional problem of a plasma expansion in vacuum between two electrodes.

Quasi-neutral fluid models for current-carrying plasmas

In this paper, we propose three formulations of a model describing a quasi-neutral plasma with non-vanishing current. These formulations are obtained by exploring the quasi-neutral limit of a two-fluid isentropic Euler system coupled with the Poisson equation. In order to study and compare the numerical efficiency of each formulation, two test-problems are implemented in one dimension. The first one is a periodic perturbation of a uniform stationary plasma. The second one is a case of plasma expansion in vacuum between two electrodes.

Trois formulations d'un modèle de plasma quasi-neutre avec courant non nul

In this Note, we propose three formulations of a model describing a quasi-neutral plasma with non-vanishing current. In order to study and compare the numerical efficiency of each formulation, two test-problems are implemented in one dimension. The first is a periodic perturbation of a uniform stationary plasma. The second is a case of plasma expansion in vacuum between two electrodes. To cite this article: P. Crispel et al., C. R. Acad. Sci. Paris, Ser. I 338 (2004).

Plasma Expansion in Vacuum: Modeling the Breakdown of Quasi Neutrality

We consider a system consisting of a vacuum gap delimited by two electrodes. A quasi-neutral plasma (ions and electrons) is injected from the cathode and expands. Electrons are emitted from the plasma-vacuum interface to the anode forming a beam. In this paper, from a two-fluid isentropic system coupled with the Poisson equation, we perform a formal asymptotic analysis. This leads to a quasi-neutral model for the plasma region and a Child--Langmuir model for the beam region. The main point of the analysis is the connection between these two models. This is done by studying a transmission layer problem. Finally, we numerically show the accuracy of the asymptotic model, comparing it to the original two-fluid model.

Dynamics of aluminum plasma produced by a nitrogen laser

13 mJ laser pulses from a nitrogen laser were focused onto an aluminum target in air. The target surface was perpendicular to the axis of the laser beam. A peak energy density of 1.3 J/cm2 and a power density of 80 MW/cm2 were achieved with a laser pulse duration of 16 ns. The high power density produced a transient plasma cloud that expanded explosively into the surrounding atmosphere. An initial electron density of about 1 × 1019 cm3 and an electron temperature of about 2eV were determined by optical spectroscopy. The line of sight was parallel to the surface and perpendicular to the laser beam axis. The height of the line of sight above the target surface was varied in order to gather data about the whole plasma cloud. In about 500 ns the plasma cloud expands to about 0.5 mm above the target surface, cools down to about 1.2eV and is tenfold reduced in electron density. The initial expansion velocity was determined to be about 2km/s. The experimentally determined plasma parameters were input into numerical models of target heating and plasma expansion. The numerical results outrule the so called outflow model of plasma expansion and show reasonable agreement with an effusion model. The observed discrepancies in observed and calculated plasma parameters are attributed to the fact that the theoretical models describe the plasma expansion in vacuum only.

Self-similar expansion of a plasma into a vacuum

The Boltzmann equilibrium for electrons has been an ad-hoc assumption of previous work about self-similar plasma expansion in vacuum. Using Boltzmann’s relation, one finds a linear electrostatic potential as a solution of the self-similar expansion. It is first shown that in such a potential, the electron behavior is exactly solvable. As a result, one finds that the exact electron density differs substantially from the Boltzmann equilibrium for moderate values of the self-similar parameter. The complete calculations of the self-similar expansion, without any assumption about the equation of state of the electrons, is presented. It is shown, in particular, that half the electron density depletion in logarithmic units is compensated for by the self-consistent modification of the electric potential. Finally, the effect is analyzed in terms of energy exchange between the electrons and the ions in the expansion.

522. Plasma expansion in vacuum and the flow of a collisionless plasma stream around a plate

522. Plasma expansion in vacuum and the flow of a collisionless plasma stream around a plate