Plasma Plume Expansion Research Articles

Collisional heating and adiabatic expansion of warm dense matter with intense relativistic electrons.

Adiabatic expansion of a warm dense Ti plasma has been observed after isochoric heating of a 100-μm-thick Ti foil with an ∼100-ns-long intense relativistic electron bunch at an energy of 19.8 MeV and a current of 1.7kA. The expansion fits well with the analytical point-source solution. After 10 J is deposited and the plasma rapidly expands out of the warm dense phase, a stable degenerate plasma (T∼1.2eV) with n_{e}>10^{17}cm^{-3} is measured for >100 ns. This is the first temporal measurement of the generation and adiabatic expansion of a large volume (3×10^{-4}cm^{3}) of warm dense plasma isochorically heated by intense monochromatic electrons. The suite of diagnostics is presented, which includes time-resolved plasma plume expansion measurements on a single shot, visible spectroscopy measurements of the emission and absorption spectrum, measurements of the beam distribution, and plans for the future.

Two directional fast imaging of plasma plume in variable magnetic field: Structure and dynamics of the plume in diamagnetic and non-diamagnetic limits

A new experimental set-up which consists of a pulse magnetic field system has been developed to capture the different phases of expanding plasma plume across the transverse magnetic field, varying from 0 to 0.57 T. Two internally synchronized ICCD cameras mounted in the orthogonal direction have been used to record the two directional projections (across and along the magnetic field directions) of the plasma plume. The plume takes the conventional ellipsoidal shape in the absence of a magnetic field. Well-defined cavity-like structures have been observed in a plane perpendicular to the field direction, which are dominant at the early stage of the plasma and comparatively lower magnetic fields. As the time evolves, the cavity changes to jet/cone-like structures which in turn change to slab-like structures with a further increase in time delay. On the other hand, well separated intensity columns (striation-like structures) appeared in a plane parallel to the magnetic field direction, which are more apparent at a higher magnetic field. Based on the projections of plume images in two perpendicular planes, the three dimensional structure of the plasma plume is modeled as an elliptical cylinder-like structure. The time dependence of dynamics and geometry of the plasma plume in the presence of a magnetic field are correlated with the expansion in diamagnetic and non-diamagnetic regimes. The validity of plasma instability, which is responsible for observed striation-like structures, is also discussed.

Modeling of Plasma Expansion during Pulsed Electron Beam Ablation of Graphite

ABSTRACTPulsed electron beam ablation (PEBA) has proven to be a promising and powerful technique for the growth of high quality thin films. Pulsed electron beam film deposition consists of many physical processes including target material heating, target ablation, plasma plume expansion, and film growth on a substrate. Plasma plume expansion into a vacuum or an ambient gas is a fundamental issue in PEBA as the quality of thin films deposited onto the substrate depends on the composition, energy and density of particles ejected from the target. In the present study, gas-dynamics equations are solved to investigate plasma expansion induced by interaction of a nanosecond electron beam pulse (∼100 ns) with a graphite target in an argon atmosphere at reduced pressure. The spatio-temporal profiles of the temperature, pressure, velocity, and density of the plasma plume are numerically simulated for a beam efficiency of 0.6 and accelerating voltage of 15 kV. The preliminary results show a rich variety of behaviors. The model is validated by comparing some of the obtained simulation results with experimental data available in the literature.

Attitude Motion of Cylindrical Space Debris during Its Removal by Ion Beam

The paper is devoted to the problem of space debris mitigation. Contactless method of the space debris deorbiting is considered. It is assumed that ion thrusters on the active spacecraft create the ion flow, which blows the debris and slows it down. The objectives of this work are the development of mathematical models and the research of space debris motion under the action of the ion flow. It is supposed that the space debris is a rigid body of a cylindrical shape. Calculation of ion beam force and torque was performed for a self-similar model of plasma plume expansion using the hypothesis of ion fully diffused reflection from a surface. A mathematical model describing plane motions of the cylindrical space debris under the influence of gravity gradient torque and the ion flux was constructed. It was shown that motion of the space debris around its center of mass has a significant effect on its removal time. Phase portraits, describing the motion of the space debris relative to its center of mass, were constructed. Comparison of the descent times in different motion modes was carried out. The results can be used to create new effective systems of large space debris removal.

Laser-induced optical breakdown spectroscopy of polymer materials based on evaluation of molecular emission bands

Laser-induced breakdown spectroscopy (LIBS) for composition analysis of polymer materials results in optical spectra containing atomic and ionic emission lines as well as molecular emission bands. In the present work, the molecular bands are analyzed to obtain spectroscopic information about the plasma state in an effort to quantify the content of different elements in the polymers. Polyethylene (PE) and a rubber material from tire production are investigated employing 157nmF2 laser and 532nm Nd:YAG laser ablation in nitrogen and argon gas background or in air. The optical detection reaches from ultraviolet (UV) over the visible (VIS) to the near infrared (NIR) spectral range. In the UV/VIS range, intense molecular emissions, C2 Swan and CN violet bands, are measured with an Echelle spectrometer equipped with an intensified CCD camera. The measured molecular emission spectra can be fitted by vibrational-rotational transitions by open access programs and data sets with good agreement between measured and fitted spectra. The fits allow determining vibrational-rotational temperatures. A comparison to electronic temperatures Te derived earlier from atomic carbon vacuum-UV (VUV) emission lines show differences, which can be related to different locations of the atomic and molecular species in the expanding plasma plume. In the NIR spectral region, we also observe the CN red bands with a conventional CDD Czerny Turner spectrometer. The emission of the three strong atomic sulfur lines between 920 and 925nm is overlapped by these bands. Fitting of the CN red bands allows a separation of both spectral contributions. This makes a quantitative evaluation of sulfur contents in the start material in the order of 1wt% feasible.

Ion and extreme ultraviolet emission features of CO2 laser produced Sn and SnO2 plasmas

The plasma plume expansion, ion debris and extreme ultraviolet (EUV) emission features of CO2 laser-produced Sn and SnO2 plasmas are investigated in this work. The expansion parameters of laser-produced plasma (LPP) are estimated using a fast-gated intensified charge-coupled device (ICCD) imaging system, while the ion debris is detected using a Faraday cup and the time-of-flight (TOF) method. Additionally, the EUV emissions from CO2 laser-produced Sn and SnO2 plasmas are measured using a grazing incidence flat-field spectrograph and EUV photodiodes. The ICCD images show that the SnO2 plasma plume has a broader edge when compared with that of the Sn plasma. Because of the differences between the thermodynamic parameters of the samples, the total ion number and the kinetic energy were both higher for the SnO2 plasma than for the Sn plasma. The maximum estimated conversion efficiencies (CEs) of the Sn and SnO2 plasmas were 1.1% and 0.9%, respectively; the difference is due to the lower Sn fraction in SnO2. The results of the angularly-resolved EUV emission measurements showed that the detected EUV energy decreases as the angle with respect to the laser axis increases.

Heterogeneous (Cu-Ti) colliding plasma dynamics

Laser ablated copper-titanium colliding plasma plume expansion at 10−4, 10−2, and 100 mbar of oxygen ambient pressures has been investigated with a view to understanding heterogeneous colliding plasma plume dynamics and the formation of multi-element stagnation layers using optical emission spectroscopy and fast imaging of plume. The observation of Cu2(A−X) and TiO−γ bands and their ambient pressure dependent emission intensity opens up the possibility of the stoichiometrically controlled formation of nanoclusters/nanocomposites.

Analysis of Plasma Created by High-Speed Impact with Triple Probe

The mechanism of destruction of a material by high-speed impact is known to be complex, and it is hard to analyze the inner state of the material during the destruction process. In particular, it is difficult to measure the temperature changes within a material during a high-speed impact. In this study, we propose a new method for estimating this temperature change by measuring the plasma produced at the impact point using a triple probe. A plasma produced by laser ablation was measured to ascertain that the triple probe actually worked. Further, some of the parameters related to the triple probe were varied, and the obtained results were compared, in order to determine the optimal parameters for measuring plasmas. A pulsed Nd-YAG laser with a fundamental wavelength of 1064 nm was employed to produce laser ablation. The laser was irradiated on a thin A2024 plate coated with a black paint. The expanding plasma plume was recorded with a high-speed camera, and the signal from the plasma was measured with the triple probe.

Electric Propulsion Subsystem Optimization for “Ion Beam Shepherd” Missions

The ion beam shepherd is an innovative contactless technique for space debris removal in which an impulse transfer thruster pushes the debris object through the action of a plasma plume and an impulse compensation thruster maintains formation flying. The optimal operational point of both thrusters strongly depends on their characteristics and on the physics of the plasma plume expansion into vacuum. With the use of dedicated thruster performance models, complemented with simplified plume expansion and plasma–debris interaction models, a system-level optimization study of the impulse transfer thruster alone and of the overall electric propulsion subsystem is presented for an ion beam shepherd mission example. An optimum design point is found for minimum overall power consumption in both cases.

The influence of plasma shielding effect on laser-ablated copper samples: a focus on signal-to-background ratio and plasma expansion

AbstractThe influence of plasma shielding effect induced by ambient gas pressure and laser intensity on the laser-produced Cu plasma parameters, signal-to-background ratio (S/B) and expansion are experimentally and numerically investigated. A Q-switched Nd:YAG laser at 1064 nm at various intensities ranging from 2 to 7.1 GW/cm2 intensity (40–150 mJ) is used to produce Cu plasma in air, argon (Ar), helium (He), and neon (Ne) ambient gas at various pressures ranging from 5 to 1000 mbar. Laser-induced breakdown spectroscopy reveals that spectral radiation, S/B, electron temperature, number density, and front edge velocity of the plasma have an increasing trend up to a certain value of laser intensity and gas pressure. Afterwards, a saturation trend is achieved, which is attributed to the shielding and self-regulation effect. The numerical modeling of the laser-produced Cu plasma in the presence of air at atmospheric pressure is carried out using the MULTI radiation hydrodynamics code. We have shown that the feature of plasma shielding effect observed in the experiments can be reproduced using a continuum hydrodynamics model. Laser intensity at about 3.5 GW/cm2 is found to produce the highest S/B at 1000 mbar air. He, Ne, air, and Ar show the best S/B, respectively and the best S/B is found for air, Ar, He, and Ne at 10, 5, 10, and 20 mbar, respectively. The expansion of plasma plume is studied using a simple and effective technique based on probe laser absorption and scattering method. The plasma plume expansion through He, Ne, air, and Ar at 1000 mbar pressure has the highest velocity, respectively. The simulated results of strong shock wave model and Rankine–Hugoniot jump condition are fitted to the experimental data, which are then used to estimate the values of the ablation parameters.

Desorption/ablation of lithium fluoride induced by extreme ultraviolet laser radiation

Abstract The availability of reliable modeling tools and input data required for the prediction of surface removal rate from the lithium fluoride targets irradiated by the intense photon beams is essential for many practical aspects. This study is motivated by the practical implementation of soft X-ray (SXR) or extreme ultraviolet (XUV) lasers for the pulsed ablation and thin film deposition. Specifically, it is focused on quantitative description of XUV laser-induced desorption/ablation from lithium fluoride, which is a reference large band-gap dielectric material with ionic crystalline structure. Computational framework was proposed and employed here for the reconstruction of plume expansion dynamics induced by the irradiation of lithium fluoride targets. The morphology of experimentally observed desorption/ablation craters were reproduced using idealized representation (two-zone approximation) of the laser fluence profile. The calculation of desorption/ablation rate was performed using one-dimensional thermomechanic model (XUV-ABLATOR code) taking into account laser heating and surface evaporation of the lithium fluoride target occurring on a nanosecond timescale. This step was followed by the application of two-dimensional hydrodynamic solver for description of laser-produced plasma plume expansion dynamics. The calculated plume lengths determined by numerical simulations were compared with a simple adiabatic expansion (blast-wave) model.

Influence of pulse width on the laser ablation of zinc in nitrogen ambient

Time-resolved spectroscopic measurements of expanding plasma plumes generated by irradiating a solid zinc target with laser pulses of 7 ns and 100 fs durations are carried out in the ambient pressure range of 0.05–200 Torr of nitrogen. At the relatively high input fluence of ~16 J/cm2, fast and slow atomic species are found to appear at different times in the optical time-of-flight (OTOF) spectra, the dynamics of which is primarily determined by the pulse duration of the excitation laser. In fs LPP, the average speed of fast species is unaffected by an increase in ambient pressure, while in ns LPP, the speed is found to reduce with pressure. The slow species shows a sharp peak in the OTOF spectra with a narrow velocity distribution for fs LPP, indicating a large number density and low electron temperature, which is consistent with optical emission spectroscopic (OES) studies. On the other hand, for ns LPP, the OTOF of slow species shows a more broadened profile which can be attributed to strong plume–laser interaction. The dynamics of slow species is heavily influenced by the presence of shock waves, which leads to the occurrence of much slower species at larger pressures.

The effects of using axial magnetic field in extreme ultraviolet photon sources for nanolithography – recent integrated simulation

AbstractWe developed a comprehensive model for simulating laser/target interaction in the presence of external axial magnetic fields. The model was integrated into the framework of the HEIGHTS-LPP computer simulation package and benchmarked with recent experimental results. The package was then used to study the angular distribution of extreme ultraviolet (EUV) photon output in plasmas produced in tin planar targets by a Nd:YAG laser. A moderate (0.5 T) permanent magnetic field does not affect EUV source evolution and output. More effective control of plasma plume expansion should be based on magnetic field gradients, that is, on the temporary varying magnetic fields as a magnetic pinch. Analysis of angular EUV output showed strong anisotropy of photon emissions. We found that the correct monitoring angle (i.e., at which the measured EUV flux corresponds to the averaged value after the correctly integrated angular distribution) does not depend on laser irradiance in the studied range and is equivalent to ~60°. We recommend arranging the EUV sensors accordingly in experiments with planar tin targets.

Positive and negative singly charged ion production of a laser induced plasma using a capillary graphite target.

A new type of laser ion source is being developed aiming at the production of positive and negative singly charged ions using a capillary graphite target structure. The initial results of the laser plasma produced inside of the 10 mm diameter conduit indicated the formation of the secondary charged particle production inside the target. A high speed camera clearly recorded the plasma plume expansion inside the target. The time-of-flight spectrum of the laser produced plasma in vacuum showed that the signal of the positive ions formed two peaks as the laser power density exceeded 10 GW/cm(2). The addition of neutral gas to the system produced a signal corresponding to negative ions after the positive signal.

Influence of surrounding gas, composition and pressure on plasma plume dynamics of nanosecond pulsed laser-induced aluminum plasmas

In this article, we present a comprehensive study of the plume dynamics of plasmas generated by laser ablation of an aluminum target. The effect of both ambient gas composition (helium, nitrogen or argon) and pressure (from ∼5 × 10−7 Torr up to atmosphere) is studied. The time- and space- resolved observation of the plasma plume are performed from spectrally integrated images using an intensified Charge Coupled Device (iCCD) camera. The iCCD images show that the ambient gas does not significantly influence the plume as long as the gas pressure is lower than 20 Torr and the time delay below 300 ns. However, for pressures higher than 20 Torr, the effect of the ambient gas becomes important, the shortest plasma plume length being observed when the gas mass species is highest. On the other hand, space- and time- resolved emission spectroscopy of aluminum ions at λ = 281.6 nm are used to determine the Time-Of-Flight (TOF) profiles. The effect of the ambient gas on the TOF profiles and therefore on the propagation velocity of Al ions is discussed. A correlation between the plasma plume expansion velocity deduced from the iCCD images and that estimated from the TOF profiles is presented. The observed differences are attributed mainly to the different physical mechanisms governing the two diagnostic techniques.

The flip-over effect in pulsed laser deposition: Is it relevant at high background gas pressures?

In pulsed laser deposition the use of a rectangular or elliptical beam spot with a non 1:1 aspect ratio leads to the so called flip-over effect. Here, the longest dimension of the laser spot results in the shortest direction of plasma plume expansion. This effect has been mainly reported for vacuum depositions of single element targets and is particularly noticeable when the aspect ratio of the beam spot is large.We investigate the flip-over effect in vacuum and at three relevant background-gas pressures for pulsed laser deposition using a La0.4Ca0.6MnO3 target by measuring the thickness dependence of the deposited material as a function of angle. The film thicknesses and compositions are determined by Rutherford backscattering and argon is used to reduce the influence of additional chemical reactions in the plasma. The results show the prevalence of the flip-over effect for all pressures except for the highest, i.e. 1×10−1mbar, where the film thickness is constant for all angles. The composition profiles show noticeable compositional variations of up to 30% with respect to the target material depending on the background gas pressure, the angular location, and the laser spot dimensions.

Element- and charge-state-resolved ion energies in the cathodic arc plasma from composite AlCr cathodes in argon, nitrogen and oxygen atmospheres

The energy distribution functions of ions in the cathodic arc plasma using composite AlCr cathodes were measured as a function of the background gas pressure in the range 0.5 to 3.5Pa for different cathode compositions and gas atmospheres. The most abundant aluminium ions were Al+ regardless of the background gas species, whereas Cr2+ ions were dominating in Ar and N2 and Cr+ in O2 atmospheres. The energy distributions of the aluminium and chromium ions typically consisted of a high-energy fraction due to acceleration in the expanding plasma plume from the cathode spot and thermalised ions that were subjected to collisions in the plasma cloud. The fraction of the latter increased with increasing background gas pressure. Atomic nitrogen and oxygen ions showed similar energy distributions as the aluminium and chromium ions, whereas the argon and molecular nitrogen and oxygen ions were formed at greater distance from the cathode spot and thus less subject to accelerating gradients. In addition to the positively charged metal and gas ions, negatively charged oxygen and oxygen-containing ions were observed in O2 atmosphere. The obtained results are intended to provide a comprehensive overview of the ion energies and charge states in the arc plasma of AlCr composite cathodes in different gas atmospheres as such plasmas are frequently used to deposit thin films and coatings.

Optimizing the synthesis of vanadium–oxygen nanostructures by plasma plume dynamics using optical imaging

The effect of an oxygen atmosphere on the expansion dynamics of a laser-produced vanadium-oxygen plasma has been investigated using a fast intensified charged-coupled device camera. We find regimes of the plasma plume expansion ranging from a free plume at vacuum and low oxygen pressures, through collisional and shock-wave-like hydrodynamic regimes at intermediate oxygen pressure, finally reaching a confined plume with subsequent thermalization of the plume particles at the highest pressure of the oxygen gas. Vanadium oxide nanostructures thin films were synthesized from this plasma and the resulting vanadium oxide phases studied as a function of the plume dynamics. We found monoclinic vanadium dioxide (VO2) (M1) and VO2 (B) nanoparticles in thin films deposited at 0.05 mbar. Pure phases of vanadium trioxide (V2O3) smooth and pentoxide (V2O5) nanorods thin films were detected at 0.01 and 0.1 to 0.2 mbar, respectively. Thin films containing VO2 (M1) were found to have a reversible metal-to-insulator transition at 61°C. This work paves the way to VO phase control by judicious choice of laser and plasma conditions.

Laser ablation dynamics in liquid phase: The effects of magnetic field and electrolyte

We examined the laser ablation dynamics of silver target in aqueous phase to explore the effects of laser power, ambient electrolytes, and magnetic field on the formation and expansion of laser-induced plasma plume, bubbles, and nanoparticles. The lifetime of the plasma emission increased with magnetic field and electrolytes, while they had no influence on the conversion of laser energy to the energy of laser-induced bubbles formed thereafter. The size of the bubbles was dependent only on the laser power.

Monte Carlo Collision method for low temperature plasma simulation

This work shows the basic foundation of the particle-based representation of low temperature plasma description. In particular, the Monte Carlo Collision (MCC) recipe has been described for the case of electron-atom and ion-atom collisions. The model has been applied to the problem of plasma plume expansion from an electric Hall-effect type thruster. The presence of low energy secondary electrons from electron-atom ionization on the electron energy distribution function (EEDF) have been identified in the first 3 mm from the exit plane where, due to the azimuthal heating the ionization continues to play an important role. In addition, low energy charge-exchange ions from ion-atom electron transfer collisions are evident in the ion energy distribution functions (IEDF) 1 m from the exit plane.