Ablated Plasma Plume Research Articles

Enabling direct kinetic simulation of dense plasma plume expansion for laser ablation plasma thrusters

Laser ablation plasma thrusters are an emerging space propulsion concept that provides promise for lightweight payload delivery. Predicting the lifetime and performance of these thrusters hinges on a comprehensive characterization of the expansion dynamics of the ablated plasma plume. While state-of-the-art techniques for simulating plasmas are often particle-based, a grid-based direct kinetic solver confers advantages in such a transient and inhomogeneous problem by eliminating statistical noise. A direct kinetic solver including interparticle collisions is employed on a plume expansion model problem spanning one dimension each in configuration and velocity space. The high degree of thermodynamic nonequilibrium inherent in plume expansion is characterized, justifying the need for a kinetic rather than a hybrid or fluid solver. Thruster-relevant metrics such as the momentum flux are also computed. The plume dynamics are observed to be highly inhomogeneous in space with insufficient time for thermalization in the region preceding the expansion front, and the theoretical possibility of reducing the local grid resolution by up to two orders of magnitude at the far end of the domain is established. These grid-point requirements are verified via the employment of nonuniform grids of various expansion ratios, several of which also employ coarsening in velocity space. Longer domain lengths are explored to characterize thruster-scale phenomena and larger ambient pressures are simulated as a testbed to probe facility effects due to collisions with background particles.

Fast imaging of laser ablation of cerium: Dependence of plasma plume dynamics and structure on native oxide growth

We have imaged the evolution of plasma following nanosecond pulsed laser ablation of cerium in air with sub-10 ns resolution. We find the ablated plasma plume expansion and shape to be strongly dependent on the time after mechanical polishing of the sample surface. After an initial shock front common to both new and aged samples (velocities up to 16 km s−1), we observe a second front that is relatively localized to the surface vicinity of newly polished samples, but in the case of older samples it moves outward at velocities of up to 4 km s−1. We attribute this behavior to the formation and growth of a native oxide layer on the order of hours after polishing. These results demonstrate that plasma imaging can be used to diagnose the presence of, and evaluate the extent of, thin surface oxides or other compounds that form soon after exposure to some atmosphere. These findings also highlight the need to explicitly consider the presence of such overlayers when modeling laser/metal interaction, when making measurements of vapor phase chemistry, and when analyzing the composition, phase, and morphology of solid particulates formed after the ablation of reactive metals.

Growth of Al-doped ZnO nanostructures in low pressure background gas by pulsed laser deposition

In this work, the deposition of nanostructures by room temperature pulsed laser deposition (PLD) in low pressure (2.6 Pa) O2, N2, He, and Ar at different substrate positions are studied. The substrates are placed at the normal on-axis/center position; and off-axis i.e. 4.5 cm above and below the center position. Optical emission spectra and ion velocity are measured by using spectrometer and ion probe. The overall intensity of optical emission is in the order of Ar > O2/N2 > He while the ion velocity is in the reverse order. The inverse relation of optical emission and ion velocity suggest that collisions of the ablated specie possibly result in strong emission and impede the ion velocity at the same time. Amorphous films are obtained for the substrates placed at on-axis/center in all the background gases and at the bottom position for O2. However, crystalline ZnO and Zn nanostructures are deposited at the bottom position in N2, He, and Ar. Larger structures are deposited in Ar and the presence of nanorods are detected by TEM. The results further suggest that in N2, He or Ar, the ablated plasma plume is spatially and thermally confined; governed by the properties of the gas. Nucleation of nanostructures occurred in the plasma plume even at low background pressure and deposited on the substrates that are placed at the bottom position. Between the two inert gases, Ar with higher atomic mass and lower thermal conductivity results in high collisions and thermal confinement that leads to some large structure as compared to those obtained in He. In addition, in the presence of N2, He or Ar, Zn crystallites are also detected, which can act as catalyst for nanostructure formation.

Long-range oscillations of a laser-produced carbon plasma recorded by an electrostatic energy analyzer

Understanding peculiar dynamics in transient laser-produced plasmas is of great importance for a number of applications such as energetic ion production, ion implantation, laser micro-machining, etc. Continuing a series of papers on the electrical and optical characterization of laser ablation plasma plumes, we report here on the observation of oscillations in the ionic and electronic currents at a long distance (17.5 cm) from the ablation target. An electrostatic energy analyzer was used to finely probe the dynamics of charge carriers in a carbon plasma generated in vacuum by KrF excimer laser ablation of a graphite target. A short-time Fourier transform data processing approach was applied to extract valuable information from the recorded currents. This method not only reveals different frequencies for two distinct expanding plasma structures, but also unveils different trends in their temporal evolution. These new experimental results corroborate previous studies supporting a scenario based on the plasma structuring in multiple double layers. A discussion with respect to an alternative scenario based on low-frequency sheath instabilities is also presented.

Influence of cavity configuration parameters on discharge characteristics of capillary discharge based pulsed plasma thruster

Capillary discharge based pulsed plasma thrusters have great prospects of applications in in-orbit maneuvering of<bold/> micro-nano satellites. In this paper, the influence of different capillary cavity structure parameters on the thruster's energy deposition process, ablation characteristics, output thrust parameters and plasma plume parameters under an energy level of 5 J were studied. The experimental results indicate that the increase of the inner diameter of the capillary cavity will significantly reduce the discharge current density, which leads the deposition energy and equivalent power to decrease; the increase of the cavity length helps to improve the energy transfer efficiency. The influence of cavity structure on the ablation characteristics is reflected in the influence of deposition energy per unit area on the tube wall temperature. When the inner diameter of the capillary increases from 1 mm to 3 mm, the ablation mass decreases significantly, and then the equivalent ablation mass remains approximately unchanged as the inner diameter of the cavity increases further; the ablation mass continues to increase as the capillary length increases, while the ablation mass per unit area continues to decrease. The impulse bit depends on the ablation mass and plasma plume velocity, and the difference in ablation characteristic further affects the plasma in the cavity. The density and equivalent pressure determine the plasma electrothermal acceleration process. The continuous increase in the diameter and length of the capillary cavity will induce the acceleration process to lag behind the discharge and ablation process. And the decrease of the deposited energy impedes the electrothermal acceleration process, which results in the decrease of the impulse bit, specific impulse, and the overall efficiency. Furthermore, the overall efficiency transfer model analysis indicates the influence of the capillary inner diameter on thruster efficiency is mainly reflected in the energy transfer efficiency, and the capillary length change mainly affects the electrothermal acceleration efficiency. The overall efficiency optimization of the thruster needs to start from increasing both energy deposition efficiency and acceleration efficiency.

A Brief Overview about Laser-Ablated Molybdenum Plasma Properties

First step in molybdenum isotope separation for medical purposes project, based in laser ablation followed by electromagnetic separation methods, is the characterization of ablated plasma plume. In this work, a depth profile emission spectroscopy study of laser-ablated molybdenum plasma expanding on air at atmospheric pressure was performed, considering Local Thermodynamic Equilibrium and one-dimensional uniform expanding models. Plasma temperature, electron density, electron population distribution and electron impact width parameter were evaluated along plasma expansion axis and reach average values of 15000 K,1018cm-3, 1% of electron populationat 4d45s6sstate and (0.017±0.008) nm, respectively. Furthermore, mean velocity of (5.0±0.7) km/sand the plasma lifetime that was (160± 14)ns for length equal to (1.80±0.05) mm weremeasured. So, this work includes a description of mainly plasma plume parameters, which permits a discussion for isotope separation methods related to laser ablation.

Synthesis of platinum nanoparticles by nanosecond laser irradiation of bulk Pt in different polar solvents

Formation of platinum nanoparticles (Pt NPs) by Nd:YAG laser ablation of a platinum target in polar solvents, viz. distilled water (DW), absolute ethanol (ET), acetone (AC), and ethylene glycol (EG), was investigated. Characterization of the NPs in terms of size distribution, shape, optical properties, phase structure, crystalline nature, and molecular structure was carried out as a function of the nature of the liquid by transmission electron microscopy, scanning electron microscopy, ultraviolet–visible (UV–Vis) absorption spectroscopy, X-ray diffraction analysis, selected-area electron diffraction analysis, Raman spectroscopy, and Fourier-transform infrared spectroscopy. The interaction of the ablation plasma plume species with species produced by decomposition of the liquid resulted in formation of spherical Pt and PtO NPs with diameter ranging from 5 nm up to a maximum of 104 nm. The results evidence that the properties of the NPs were affected by the nature of the liquid, including thermodynamic parameters such as the dipole moment, boiling point, and viscosity.

Investigation of Intermixing/Implantation in Pulsed Laser Deposited Metallic Cr/Ni80Fe20 and Ni80Fe20/Polypyrrole Multilayer Thin Films

Cr/Ni80Fe20 and Ni80Fe20/Polypyrrole multilayer thin films were prepared by pulsed laser deposition in vacuum and in Argon background gas at different pressures. Intermixing/implantation at their interfaces were investigated by scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS) analysis. Surface morphology (step height and roughness) of these samples were carried out by atomic force microscopy (AFM) and magnetic property (saturation magnetic flux) measurement by hysteresis loop tracer. The magnetic and surface morphology characterisations were used to calculate the interfacial mixing and/or implantation depth which have been found to agree with direct measured values. A correlation of these intermixing depths with Monte Carlo simulations of ion bombardment in the deposition process, using Stopping range of ion in matter (SRIM) incorporated with Transport of ion in matter (TRIM) gave the energy of the most implanted ionic species in a very simple way. Under high vacuum pressure, intermixing/implantation depth at the interfaces was high and occurs due to the presence of energetic species in the ablated plasma plume. With Argon gas background of increasing pressure, a reduction in energetic species energy is followed with a decrease in intermixing/implantation depth and the scattering of the ablated species leads to a decrease in the growth rate of Cr. An Argon background gas pressure of 20 mTorr gave the kinetic energy of the most energetic Cr species as 150 eV (from simulation) with 0.61 nm intermixing/implantation depth, while the vacuum pressure of 1.3 × 10− 7Torr gave the most energetic Cr energy as 3.2 keV with 2.38 nm depth of intermixing. Vacuum pressure 5 × 10− 7Torr with deposition of Permalloy (Py) Ni80Fe20 into polypyrrole gave measured intermixing/implantation depths of 6.81 nm with Ni80Fe20 energy of about 800 eV. The surface of the Py/polypyrrole (Ppy) was very rough at vacuum pressure 5 × 10− 3 Torr deposition as confirmed by the atomic force microscope measurement and STEM image than under background gas pressure 1 × 10− 3 Torr deposition. This is helpful for stoichiometric preparation of metallic multilayer thin films with well defined individual sharp interfaces and surface.

Oxide or carbide nanoparticles synthesized by laser ablation of a bulk Hf target in liquids and their structural, optical, and dielectric properties

Laser ablation of a bulk Hf target in deionized (DI) water, ethanol, or toluene was carried out for the production of nanoparticles' colloidal solutions. Due to the interaction of the ablation plasma plume species with the species which are produced by the liquid decomposition at the plume-liquid interface, hafnia (HfO2) nanoparticles are synthesized in DI water, hafnium carbide (HfC) nanoparticles in toluene, and a mixture of these in ethanol. The hafnia nanoparticles are in the monoclinic low temperature phase and in the tetragonal and fcc high temperature phases. Their size distribution follows log-normal function with a median diameter in the range of 4.3–5.3 nm. Nanoparticles synthesized in DI water have band gaps of 5.6 and 5.4 eV, in ethanol 5.72 and 5.65 eV (using low and high pulse energy), and in toluene 3 eV. The values for the relative permittivity in the range of 7.74–8.90 were measured for hafnia nanoparticles' thin films deposited on substrates by drop-casting (self-assembled layers) in parallel plate capacitor structures.

Characterization of Carbon Plasma Evolution Using Laser Ablation TOF Mass Spectrometry**supported by the National Magnetic Confinement Fusion Science Program of China (No. 2013GB109005) and National Natural Science Foundation of China (No. 11175035), Chinesisch-Deutsches Forschungs Project (GZ768), the Fundamental Research Funds for the Central Universities of China (Nos. DUT12ZD(G)01, DUT14ZD(G)04) and MMLab Research Project (DP1051208)

In this work, a time-of-flight (TOF) mass spectrometer has been used to investigate the distribution of intermediate species and formation process of carbon clusters. The graphite sample was ablated by Nd:YAG laser (532 nm and 1064 nm). The results indicate that the maximum size distribution shifted towards small cluster ions as the laser fluence increased, which happened because of the fragmentation of larger clusters in the hot plume. The temporal evolution of ions was measured by varying the delay time of the ion extraction pulse with respect to the laser irradiation, which was used to provide distribution information of the species in the ablated plasma plume. When the laser fluence decreased, the yield of all of the clusters obviously dropped.

Discriminating between the Role of Phase Matching and that of the Single-Atom Response in Resonance Plasma-Plume High-Order Harmonic Generation.

Resonance enhancement of high-order harmonic generation has recently been found in the interaction of intense ultrashort laser pulses with laser ablated plasma plumes. It is a promising route towards the production of an intense and coherent extreme ultraviolet radiation source. However, the mechanism of this resonance enhancement is still not clear. There are two possible explanations; one relies on a better recombination cross section through an autoionization state in the single-atom response. The other relies on improved phase matching conditions around the resonance. Here, we try to discriminate between these two conjectures by measuring coherence lengths of the harmonics, both on resonance and off resonance. Our findings support the single-atom response hypothesis.

Plasma plume behavior of laser ablated cerium oxide: Effect of oxygen partial pressure

AbstractThis paper describes the spatial and temporal investigation of laser ablated plasma plume of cerium oxide target using Langmuir probe. Cerium oxide target was ablated using a KrF (λ ~ 248 nm) gas laser. Experimental studies confirmed that oxygen partial pressure of 2 × 10−2mbar is sufficient enough to get good quality films of cerium oxide. At this pressure, plume was diagnosed for their spatial and temporal behavior. Spatial distribution was investigated at a distance of 15 mm, 30 mm, and up to a maximum distance of 45 mm from the target, whereas temporal behavior has been recorded in the range of 0 to 50 µS with an interval of 0.5 µS. The average electron densities are found to be maximum at 30 mm from the target position and the plasma current of the laser ablated ceria is found to be maximum at 22 µS.

Time evolution of the infrared laser ablation plasma plume of SiO

The spatio-temporal evolution of the silicon monoxide SiO plasma produced by a high-power CO2 pulsed laser has been investigated using optical emission spectroscopy (OES) and imaging methods. The formed plasma was found to be strongly ionized, yielding Si+, O+, Si2+, O2+ and Si3+ species, rich in neutral silicon and oxygen atoms, and very weak molecular bands of SiO time-integrated and time-resolved two-dimensional OES plasma profiles were recorded as a function of emitted wavelength and distance from the target. The temporal behavior of specific emission lines of Si, Si+, O+, Si2+ and O2+ was characterized. The results show a faster decay of O2+ and Si2+ than that of O+, Si+ and Si. The Stark broadening of isolated single-ionized silicon emission lines was employed for deducing the electron density during the plasma expansion. The relative intensities of two Si2+ lines were used to calculate the time evolution of the plasma temperature.

Laser ablated copper plasmas in liquid and gas ambient

The dynamics of copper ablated plasma plumes generated using laser ablation of copper targets in both liquid (de-ionized water) and gas (air) ambients is reported. Using time and space resolved visible emission spectroscopy (450-650 nm), the plasma plumes parameters are investigated. The electron density (ne) determined using Stark broadening of the Cu I (3d104d1 2D3/2-3d104p1 2P3/2 at 521.8 nm) line is estimated and compared for both plasma plumes. The electron temperature (Te) was estimated using the relative line emission intensities of the neutral copper transitions. Field emission scanning electron microscopy and energy dispersive x-ray spectral analysis of the ablated copper surface indicated abundance of spherical nanoparticles in liquid while those in air are amalgamates of irregular shapes. The nanoparticles suspended in the confining liquid form aggregates and exhibit a surface plasmon resonance at ∼590 nm.

Femtosecond envelope of the high-harmonic emission from ablation plasmas

We characterize the temporal profile of the high-order harmonic emission from ablation plasma plumes using cross-correlations with the infrared (IR) laser beam provided by two-photon harmonic+IR ionization of rare gas atoms. We study both non-resonant plasmas (lead, gold and chrome) and resonant plasmas (indium and tin), i.e. plasmas presenting in the singly charged ions a strong radiative transition coinciding with a harmonic order. The cross-correlation traces are found to be very similar for all harmonic orders and all plasma targets. The recovered harmonic pulse durations are very similar to the driving laser, with a tendency towards being shorter, demonstrating that the emission is a directly laser-driven process even in the case of resonant harmonics. This provides a valuable input for theories describing resonant-harmonic emission and opens the perspective of a very high flux tabletop XUV source for applications.

Material Dependence on Plasma Shielding Induced by Laser Ablation

Plasma shielding is an important concept to study if the material damage could be suppressed with plasma layer properly prepared by absorbing the incoming plasma flux onto a divertor target in MFE or the first wall in IFE reactors. First experimental evidence of this effect is reported. Two plasma plumes (n∼ 1012/cm3, Te ∼ 1 eV) are created with two laser beams. The laser ablation plasma plumes are created at laser energy density up to 10 J/cm2 and are crossed each other. 12∼59 % of the incoming plasma particles are shielded with the collisions of the other plasma plume. By observing the material dependence of colliding effects, the effect to plasma shielding is discussed. c © 2012 The Japan Society of Plasma Science and Nuclear Fusion Research

Aerosol formation and hydrogen co-deposition by colliding ablation plasma plumes of lithium and lead

In a high-repetition inertial fusion reactor, along with pellet implosions, the interior of target chamber is to be exposed to high-energy, short pulses of X-ray, unburned DT and He ash particles and pellet debris. As a result, wall materials will be subjected to ablation, ejecting particles in the plasma state to collide with each other in the center of volume. The interaction dynamics of ablation plasmas of lithium and lead, candidate first wall materials, has been investigated in the deposited energy density range from 3 to 10J/cm2/pulse at a repetition rate of 10Hz, each 6ns long. The plasma density and electron temperature of colliding ablation plumes have been found to vary from the order of 108–10131/cm3 and from 0.7 to 1.5eV, respectively. The formation of aerosol in the form of droplet has been observed with diameters between 100nm and 10μm. Also, hydrogen co-deposition has been found to occur particularly for colliding plumes of lithium, resulting in the H/Li atomic ratio from 0.15 to 0.27 in the hydrogen partial pressure range from 10 to 50Pa.

Fast Imaging of Ablation Plasma Produced by a Pulsed Electron Beam

The expansion of the ablation plasma plume produced at the interaction of a pulsed electron beam with a target is studied by fast imaging. The plasma plume has a forward-peaked pattern, with a slight spatial deviation from the normal to the target due to the presence of the capillary tube of the channel-spark electron source near the target. The emitting plasma species have energies between 10 and 60 eV.

Aerosol Formation and Hydrogen Co-Deposition by Colliding Ablation Plasma Plumes of Carbon

Along with pellet implosions, the interior of an inertial fusion reactor will be exposed to intense and short pulse power fluxes, leading to materials ablation. Ablated materials will either collide with each other in the axis-of-symmetry region or be re-deposited elsewhere in the target chamber. The present work is intended to investigate the behavior of colliding ablation plasma plumes and that of materials re-deposition in hydrogenic atmosphere. Laser-ablation plasma plumes of carbon are set to collide with each other in a laboratory-scale experimental setup. Results indicate that carbon cluster ions are formed, including C2+ C3+ C4+ C5+ and C6+, some of which grow into aerosol in the form of micro/nano carbon structure. Also, it has been found that ablated carbon and hydrogen can form co-deposited layers with the H/C ratio, reaching the order of 0.1.

Laser plasma plume structure and dynamics in the ambient air: The early stage of expansion

Laser ablation plasma plume expanding into the ambient atmosphere may be an efficient way to produce nanoparticles. From that reason it would be interesting to study the properties of these laser induced plasmas formed under conditions that are known to be favorable for nanoparticles production. In general, plume behavior can be described as a two-stage process: a “violent” plume expansion due to the absorption of the laser beam energy (during the laser pulse) followed by a fast adiabatic expansion in the ambient gas (after the end of the laser pulse). Plasma plume may last a few microseconds and may have densities 10−6 times lower than the solid densities at temperatures close to the ambient temperature. Expansion of the plasma plume induced by the impact of a nanosecond laser beam (λ = 1064 nm) on the surface of metallic samples in the open air has been investigated by means of fast photography. Spatio-temporal evolution of the plume at the early stage of its expansion (first 330 ns) has been recorded. Structure and dynamics of the plasma plume have been investigated and compared to numerical simulations obtained with a hydro-code, as well as some scaling laws. In addition, measurements using different sample materials (Al, Fe, and Ti) have been performed in order to analyze the influence of target material on plume expansion.