Plasma Plume Expansion Research Articles

Target-Plasma Expansion Induced by 20-MeV Intense Electron Beam

The typical response of an X-ray converter material to the passage of a high-current relativistic electron beam is ionization and rapid dispersal. Experiments have been performed on the Dragon-I linear induction accelerator to study this phenomenon. In this paper, we report the fast photography and Faraday cup experiments performed to quantify the plasma-plume expansion and velocities of ions. Monte Carlo simulation shows that the energy deposition in a multilayer target is about 7 kJ/g. By solving the Saha equation, the ionization degree of the plasma was figured out to be only 14%.

Al and Zn film deposition using a vacuum arc plasma source with a refractory anode

The radially expanding plasma plume generated in a Hot Refractory Anode Vacuum Arc was used to deposit thin Al and Zn films on glass substrates. The electrode separation was 10mm, arc time varied up to 165s, and current (I) was 100–225A. The cathode was a water-cooled Al or Zn cylinder. A graphite anode with 9 or 30mm height was used with the Al cathode, and 10 or 30mm height Mo anode was used with the Zn cathode. A mechanical shutter controlled the substrate exposure onset and duration (15s) to the anodic plasma. The distance from the arc axis to the substrate (L) was varied between 80 and 165mm. The film thickness was measured with a profilometer, and macroparticle (MP) presence on the coating surface was examined by optical microscopy.It was found that the deposition rate increased as a function of time to a peak, and then decreased to a steady-state value. The peak occurred sooner using the 9mm anode than with the 30mm anode. The peak deposition rate increased and the peak time decreased with I. The steady-state deposition rate was larger for Zn (~2μm/min) than for Al cathodes (~1μm/min) at I=225A and L=110mm. The arc voltage for Al was ~20–22V and for Zn it was 11V. The deposition rate peak appeared due to MPs evaporating from the hot anode, where they had initially condensed during the conventional arc stage when the anode was still cold. This effect was significant with low melting temperature Al and Zn cathodes, and negligible with Cu and Ti cathodes studied previously.

Plasma dynamics of a confined extreme ultraviolet light source

Laser plasmas were generated by ablation of aluminum targets via a Nd:YAG glass laser, of pulse energy 0.8 J, and duration 15 ns (full width at half maximum) at the fundamental wavelength (1.064 μm). Emission lines in the wavelength range of 27–32 nm (45–37.8 eV) were mapped over a spatial range extending out 1.8 mm from the target surface and for a temporal range of 42 ns after the termination of the laser pulse. Two targets were utilized: a planar surface and a rectangular cavity. The latter was composed of a rectangular shaped cavity of depth 3 mm and height 1.2 mm, cut into an aluminum massive. An irradiance of Ip∼1011 W/cm2 was delivered to both targets and the confining influence of the rectangular cavity upon plasma formation and expansion was studied. Diagnostics of the emitted spectra reveal the unique dynamics of restricted plasma plume expansion, which results in plasma-surface collisions and subsequent plasma rebound within the cavity. These effects give rise to strong enhancement of both continuum and line emission in the contained plasma plume. These enhancements are especially evident for the more highly charged ions. Superior emission from plasma-surface collisions are associated with “forced recombination” during early time scales, while enhanced emission at later stages are associated with plasma plume component rebound and collision.

Material ablation and plasma plume expansion study from Fe and graphite targets in Ar gas atmosphere

Study of expansion dynamics of pulsed-laser ablation plasmas from Fe and graphite targets is presented. A 532 nm Q-switched Nd:YAG laser with fluence of 30 J cm−2 is used to ablate the Fe and graphite targets in various Ar ambient gas pressures. Plasma ablation parameters for the two target materials are estimated using snow-plow and shock-wave models, which show that the laser beam energy deposited to ablated species remains at 70% for both targets at all ambient pressures. The plume splitting was observed, more prominently, for Fe plasma as it moves faster compared to graphite plasma. The difference in plasma plume fronts’ speeds for different targets was attributed to the significant difference in mass of the ablated plasma for two targets, as estimated from simulation results.

Effect of ZnO plasma plume dynamics on laser ablation

The dynamic behaviors and optical properties of a ZnO plasma plume produced by pulsed laser ablation using a Nd:YAG laser (wavelength: 532 nm, pulse width: 3 ns) were studied by fast photography using a commercial gated charge coupled device (CCD) camera linked with a delay circuit and by optical emission spectroscopy at various ambient oxygen pressures. Fast photography was conducted with a resolving power of 0.25 μs and the expansion behaviors of the laser ablation plume were observed. Plasma plume expansion velocity decreased with oxygen partial pressure. The flow of the plasma plume in the early stage of expansion of up to 3 ms agreed well with the drag model.

Proton deflectometry of a magnetic reconnection geometry

Laser-driven magnetic reconnection is investigated using proton deflectometry. Two laser beams of nanosecond duration were focused in close proximity on a solid target to intensities of I∼1×1015 W cm−2. Through the well known ∇ne×∇Te mechanism, azimuthal magnetic fields are generated around each focal spot. During the expansion of the two plasmas, oppositely oriented field lines are brought together resulting in magnetic reconnection in the region between the two focal spots. The spatial scales and plasma parameters are consistent with the reconnection proceeding due to a Hall mechanism. An optimum focal spot separation for magnetic reconnection to occur is found to be ≈400±100 μm. Proton probing of the temporal evolution of the interaction shows the formation of the boundary layer between the two expanding plasma plumes and associated magnetic fields, as well as an instability later in the interaction. Such laboratory experiments provide an opportunity to investigate magnetic reconnection under unique conditions and have possible implications for multiple beam applications such as inertial confinement fusion experiments.

Characterization of plasma propulsion by Nd:YAG laser

Significant propulsion parameters, specific impulse and coupling coefficient for the different metallic pendulums are presented. 4 N (99.99%) pure, solid targets are in the form of foils of aluminium, copper and gold. The targets are irradiated by Q-switched pulsed Nd:YAG laser (1064 nm, 10 mJ, 1.1 MW, 9–14 ns) under standard conditions of temperature and pressure. Plasma plume of these targets is also observed by employing CCD (BOSCH LTC0510, monochrome camera) based, computer controlled image capturing system and it was seen that expansion of plasma plume for oscillating targets is anisotropic in air. The results reveal that not only very high exhaust velocity of propellant 10 6 m/s is achieved but also very specific impulse values of Al, Cu and Au targets (3.14 × 10 6 s, 1.37 × 10 7 s, 7.16 × 10 5 s respectively) are obtained. Coupling coefficients are for Al, Cu and Au were 1.54 × 10 3 (N-s/J), 1.88 × 10 3 (N-s/J), and 1.08 × 10 3 (N-s/J) respectively.

Synthesis and Characterization of Nanoparticles and Nanocrystalline Functional Films

This work reports on spectroscopic investigations of interaction of an expanding laser ablated plume of aluminum, zinc, graphite with ambient atmosphere of oxygen and nitrogen gas and the formation of nitrides and oxides. The ambient pressure and fluence dependence on the reactive process occurring in the ablated plume responsible for formation of oxides and nitrides is discussed. Fast photography/imaging technique using intensified charge coupled device (ICCD) is gaining importance as a diagnostic tool for understanding the dynamics of the expanding plasma plume and the gas phase nanoparticle synthesis, thus providing a novel way to understand the transportation of nanoparticles and of control of particle size. Two dimensional images of the expanding plasma plume were captured using ICCD to understand the role of vapor and shock temperature. A comprehensive study done on oxide and nitrides films using pulsed laser deposition technique for possible laser oscillations in UV region of electromagnetic spectrum is presented.

Parametric study of expanding plasma plume formed by laser-blow-off of thin film using triple Langmuir probe

The triple probe technique has been used to study the parameters of flowing plasma plume formed by laser-blow-off (LBO) of a multicomponent LiF–C target. The advantages of triple Langmuir probe over the single probe have been discussed with regard to the present study. Our results show that triple probe is better suited for parametric measurements close to the target. The spatiotemporal evolutions of electron density and temperature were measured in different ambient environments and for various laser fluences. The angular distribution of electron density and temperature was also measured. It was found that the presence of ambient gas drastically affects the electron density and temperature of the LBO plume. Large enhancement in ne and Te at intermediate pressures (10−2 Torr) is expected due to increase in collisional processes. On the other hand, laser fluence does not affect the observed ne and Te significantly. In vacuum, a new phenomenon, i.e., an oscillation in the trailing portion of the plasma plume at a closer distance from the target, is also reported.

Particles formation in an expanding plasma

Interaction of a laser beam with a target generates a high velocity expanding plasma plume, solid debris and liquid nano- and microparticles. They are produced from plasma recombination and vapor condensation and can be deposited on optical elements located nearby the target. Two distinct kinds of particles were observed depending on the temperature achieved in the plasma plume: large micrometer-size fragments for temperatures lower than the critical temperature, and very small nanometer-size particles for higher temperatures. The paper presents experimental observations of fragments and nanoparticles in plasma plumes and a comparison with models.

Measurement of the Vacuum Arc Plasma Force

The axial force carried by the expanding plasma plume from 50-250-A copper and aluminum vacuum arcs was measured using a pendulum whose axle was equipped with a rotary optical encoder. It was found that the force was a linear function of current. The electrode geometry was varied to find the maximum force. At maximum, the average forces per unit current were 21.4 dyn/A for aluminum cathodes and 36.1 dyn/A for copper cathodes. The Cu ion current fraction was measured to be 8.6%.

C 2 and CN dynamics and pulsed laser deposition of CNx films

The time-resolved optical emission studies of laser ablated carbon plasma in nitrogen ambient are carried out to understand the dynamic of formation of C2 and CN for depositing quality thin films. An optimum formation of C2 is observed at 3 mm from the target surface and 350 ns after the initiation of plasma. However, CN is formed at comparatively larger distance, 4 mm, and larger delay (850 ns). The expanding plasma plume splits/bifurcates into slow and fast moving two distinct components, with the faster components further splitting up at later times (>350 ns) into two components. The estimated plume front velocity from plume imaging in the nitrogen ambient of 1.2 mbars at a delay of 100 ns is 3.8×106 cm/s, consistent with spectroscopic measurement ∼3.0×106 cm/s. The CNx thin films deposited by pulsed laser deposition technique are characterized by x-ray diffraction, atomic force microscopy, and Raman spectroscopy. The high ID/IG ratio and peak position shift of G band to lower values in the films deposited for longer time indicates the high incorporation of nitrogen and increasing CN concentration within the film.

The Plasma Plume Emitted Onboard the International Space Station Under the Effect of the Geomagnetic Field

The International Space Station is equipped with the plasma-contactor unit that emits plasma. We demonstrate that the geomagnetic field strongly affects plasma-plume expansion, resulting in recurrent changes of Station plasma environment. We further present a method of calculating the plasma-plume characteristics and compare the prediction with the flight data.

Emission spectra investigation of fs induced NPs probed by the ns laser pulse of a fs/ns DP-LIBS orthogonal configuration

A dual-pulse fs/ns laser induced breakdown spectroscopy configuration, where an initial 250 fs ablating pulsed laser followed by a delayed ns laser beam placed at a fixed distance, orthogonally with the expanding plasma plume, has been used in air on a Al 65Cu 23Fe 12 quasicrystal. The obtained emission data were acquired with a set-up arrangement providing space detections, with a resolution up to 15 μm, of the ns laser pulse generated signals. Assuming the fulfillment of local thermodynamic equilibrium conditions, the role played by the time lag between the two laser beams on the induced plasma excitation temperatures and electronic densities, as well as a space resolved process survey, has been followed. The spatial and time resolved spectra show, almost, steady values of the determined elementary plasma features with the development of nanoparticles occurring during the fs laser pulsed ablation process. The ns laser probe of the dual-pulse LIBS configuration here presented confirms that the nanoparticles induced can be largely widespread in both space and time whose compositions, overall, could retain the starting target stoichiometry. It is shown that these nanoparticles formation can actually take place at different times following the initial ultra-short laser beam incidence and that, especially at long inter-pulse delays (>100 μs), modest compositional changes can be observed.

Nanostructured high valence silver oxide produced by pulsed laser deposition

Among silver oxides, Ag 4O 4, i.e. high valence Ag(I)Ag(III) oxide, is interesting for applications in high energy batteries and for the development of antimicrobial coatings. We here show that ns UV pulsed laser deposition (PLD) in an oxygen containing atmosphere allows the synthesis of pure Ag 4O 4 nanocrystalline thin films, permitting at the same time to control the morphology of the material at the sub-micrometer scale. Ag 4O 4 films with a crystalline domain size of the order of tens of nm can be deposited provided the deposition pressure is above a threshold (roughly 4 Pa pure O 2 or 20 Pa synthetic air). The formation of this particular high valence silver oxide is explained in terms of the reactions occurring during the expansion of the ablated species in the reactive atmosphere. In particular, expansion of the PLD plasma plume is accompanied by formation of low stability Ag–O dimers and atomic oxygen, providing reactive species at the substrate where the film grows. Evidence of reactive collisions in the expanding ablation plume is obtained by analysis of the plume visible shape in inert and reactive atmospheres. In addition, we show how the dimensionless deposition parameter L, relating the target-to-substrate distance to the ablation plume maximum expansion length, can be used to classify different growth regimes. It is thus possible to vary the stoichiometry and the morphology of the films, from compact and columnar to foam-like, by controlling both the gas pressure and the target-to-substrate distance.

A Numerical Algorithm for Magnetohydrodynamics of Ablated Materials

A numerical algorithm for the simulation of magnetohydrodynamics in partially ionized ablated material is described. For the hydro part, the hyperbolic conservation laws with electromagnetic terms is solved using techniques developed for free surface flows; for the electromagnetic part, the electrostatic approximation is applied and an elliptic equation for electric potential is solved. The algorithm has been implemented in the frame of front tracking, which explicitly tracks geometrically complex evolving interfaces. An elliptic solver based on the embedded boundary method were implemented for both two- and three-dimensional simulations. A surface model on the interface between the solid target and the ablated vapor has also been developed as well as a numerical model for the equation of state which accounts for atomic processes in the ablated material. The code has been applied to simulations of the pellet ablation in a magnetically confined plasma and the laser-ablated plasma plume expansion in magnetic fields.

Cluster growth in an ablation plume propagating through a buffer gas

A phenomenological mixed-propagation model that describes the expansion of an ablation plume through a buffer gas is introduced. Selected experiments including LaMnO3 and tin ablation in oxygen, as well as tungsten ablation in argon, are analysed. For given ablation conditions the expansion parameters required to model the growth of clusters in the expanding plasma plume are deduced and the average asymptotic size of the clusters is calculated and compared (for tungsten) with the size of clusters measured by transmission electron microscopy.

Modelling the propagation of an ablation plume in a gas

Pulsed laser ablation gives rise to an expanding microplasma that consists of the evaporated species, energised by the photons in the tail of the laser pulse. The values of the process parameters, including laser energy density, wavelength and pulse duration, besides the presence of a specific buffer gas at a given pressure, affect the expansion of the ablation plasma plume. After a discussion of the analytical models available in the literature to describe the propagation of an ablation plume, it is shown that by a combined-propagation model, based on a modification of the diffusion and the drag models, the characteristics of plume expansion can be predicted. Model parameters are directly extracted from the available experimental parameters. By combined-propagation model, the expansion of ablation plumes from elemental targets of silicon, silver, tin and tungsten, vapourised in inert gases and in oxygen at different pressures is analysed.

Experimental observations and modeling of nanoparticle formation in laser-produced expanding plasma

Interaction of a laser beam with a target may generate a high velocity expanding plasma plume, solid debris, and liquid nano- and microparticles. They can be produced from plasma recombination, vapor condensation or by a direct expulsion of the heated liquid phase. Two distinct sizes of particles are observed depending on the temperature achieved in the plasma plume: Micrometer-size fragments for temperatures lower than the critical temperature, and nanometer-size particles for higher temperatures. The paper presents experimental observations of fragments and nanoparticles in plasma plumes created from gold targets. These results are compared with theoretical models of vapor condensation and microparticle formation.

Influence of the focal point position of a focusing lens on a character of an ablative plasma expansion

This paper is devoted to explanation, why at a fixed spot diameter of the partly defocused laser beam on the target surface the possibility of creating plasma jets depends strongly on the relative position of the focusing lens focal point to the target surface, i.e. whether it is located inside or in front of the target. We demonstrate how the focal point position can influence properties of the expanding plasma plume and, therefore, substantially change conditions for plasma jet forming. The results of this paper have evidently proved that the plasma strongly modifies the initial distribution of the laser intensity. A change of the laser intensity distribution due to plasma interaction involves also changing the plasma properties, e.g. tendency to the plasma jet forming.