Plasma Explosion Research Articles

Shock induced variable density flows in the vacuum microchannel: I. medium laser fluence

Laser-matter interactions with metal target cause plasma explosion and shock accelerated variable density flow instabilities in the Semiconfined Configuration (SCC). Their study gives deeper insight into the flow instabilities present in all microchannel devices. Blast wave motion along the SCC microchanel causes the Kelvin–Helmholtz (KH) instability and formation of vortex filaments for the critical Reynolds number. Appearing in all shear layers—it affects the fluid transport efficiency. Shear layer acceleration causes a Raleigh-Taylor instability (RTI). Oriented bubble growth by discrete merging indicates anisotropic RTI mixing. Similar RTI flame instability appears in the conversion of chemical energy into electricity affecting microcombustion efficiency. Another case of anisotropic RTI is the flow boiling for cooling of chips and microelectronic devices. The RTI boiling which appears for the critical heat flux is based on rising surface vapor columns (oriented bubble growth) with liquid counterflow (spike prominences) for the critical wavelength at density interface. The RT bubble merging graph trees determine turbulent mixing which affects the heat transfer rates. Bottom-wall turbulent flow in the SCC microchannel causes streaks of the low momentum fluid and formation of hairpin vortex packets with lattice organization. This makes possible to quantify parameters responsible for the evolution of hairpin vortex packets in the microchannel devices. Appearing from the low to the high Reynolds numbers they affect the transport properties, control of the fluid motion, enhancement of mixing, or the separation of fluids. Fluid particle ejecta—thin supersonic jets - evolve into long needle-like jets which start spiraling, helical pairing and swirling in the field of thermal gradients. Such instabilities appear in the microcombustion flame instability and in the space micropropulsion systems. Oscillating and spiral flames appear in the presence of thermal gradient in the microchannel, due to the combined effects of thermal gradient fields and the mixture flow rates.

Numerical Simulation of Acoustic Wave Generated by DC Corona Discharge Based on the Shock Wave Theory

The audible noise generated by corona discharge has the N-type characteristic at the initial generation stage, and it is a typical shock wave. This shock wave usually only exists around the corona source with a tiny range, making it difficult to obtain its characteristics through experimental measurements. An electrosound-combined simulation of the corona discharge based on the shock wave theory was conducted, and the development process involving the corona discharge, shock wave, and sound wave was simulated. First, the corona was numerically simulated based on the 2D pin–plate axisymmetric hydrodynamic model. It was found that the plasma was mainly distributed near the axis of the corona field where the electric field changed violently, and the maximum value of the electric field appeared at the head of the discharge channel. Then, the plasma energy was equivalent to the explosive energy, and a plasma explosion shock model was established. It was found that the shock wave pressure had obvious positive and negative pressure zones, and the propagation velocity decays to the sound velocity gradually. Finally, the shock wave pressure derived by the explosion model was used as the acoustic source, and the acoustic wave propagation process was simulated. The simulated sound pressure waveform had the same characteristics as the relevant experimental measurement results, proving that the developed method possessed strong applicability and gave rise to a new angle for the simulation of corona-generated audible noise.

Detection of trace metals in water by filament- and plasma-grating-induced breakdown spectroscopy

Filament- and plasma-grating-induced breakdown spectroscopy (F-GIBS) was demonstrated as an efficient technique for sensitive detection of metals in water, where plasma gratings were established through synchronized nonlinear interaction of two noncollinear filaments and an additional filament was generated with another fs laser beam propagating along their bisector. A water jet was constructed vertically to the three co-planar filaments, overcoming side effects from violent plasma explosion and bubble generation. Three distinct regimes of different mechanisms were validated for nonlinear couplings of the third filament with plasma gratings. As the third filament was temporally overlapped with the two noncollinear filaments in the interaction zone, all the three filaments participated in synchronous nonlinear interaction and plasma grating structures were altered by the addition of the third filament. As the third filament was positively or negatively delayed, the as-formed plasma gratings were elongated by the delayed third filament, or plasma gratings were formed in the presence of plasma expansion of the ahead third filament, respectively. Using F-GIBS for trace metal detection in water, significant spectral line enhancements were observed.

Evolution of nanosecond laser-induced phase explosion based on a high-speed continuous imaging system

A high-speed continuous imaging system is established based on the principle of multiwavelength shadow imaging with a 15-ns exposure time and 1-ns frame interval. Furthermore, the spatiotemporal evolution of phase explosion products induced by Nd: YAG nanosecond laser ablation of aluminum was observed. The results show that, at the laser flux of 1.34 J/cm2, only shockwave is caused by strong evaporation; above the laser flux of 2.05 J/cm2, the shadow image shows significant explosive particles jet. When the injected laser flux reaches 3.32 J/cm2, the plasma explosion is accompanied by the phase explosion. Moreover, at a laser flux between 1.34 and 2.05 J/cm2 the velocity of shockwave fronts surges owing to the phase explosion. At a laser flux of 2.86–3.32 J/cm2, the wavefront velocity resurges under the effects of phase explosion and plasma explosion.

Explosion of thin flat foils with periodical modified structure

The fast Z-pinch plasma formation, exploding dynamics, and the evolution of the instability can be controlled experimentally by making special structures on metal surface layer to change the initial state of material, which is valuable for studying the Z-pinch physics. Experiments on the explosion of thin flat foils which have been etched into a periodical structure on surface are performed on the QG-1 facility (～1.4 MA peak current, ～100 ns rise time) in order to study the effects of different surface conditions on explosion and control the evolution of the instability in fast Z-pinch plasma. A kind of inverse load configuration is used in experiment in which the return current post is set at the central axial-position and two modified flat foils are strained outside symmetrically as the main load. So the corresponding <i> <b>J</b> </i> × <i> <b>B</b> </i> force directs outward from the return current post orthogonal to the foil plane, creating an acceleration and pushing the foil plasma away from the center in this configuration. Different surfaces of the foil are also investigated in different conditions because of the asymmetric magnetic field distribution which is useful to study the different evolutions of instability. The foils used in the experiment mainly are the 30-μm-thick aluminum foil. The wavelength of groove perturbations seeded on the surface is 2 mm wide and ～10 μm deep. The plasma explosion dynamic behaviors around conditioned area are diagnosed by laser shadowgraphy, laser interferometry, multiframe optical self-emission imaging and B-dot. It is found that the initially etched periodical structure on surface can control the plasma structure in exploding process which can be concluded as follows. Developing plasma structure shows a periodic character similar to the initial surface structure and the eigenwavelength of the Al is suppressed. In the meantime, the surface without etched perturbations is also influenced by the etched side, showing a similar instability structure but with a lower amplitude. The correlation between two surfaces turns stronger than the case of normal foils. A faster expanding rate occurs in the deep region of the initial periodical groove structure which causes a reverse structure to form. In the discontinuous area of the conditoned structure, a narrow stream of plasma jets perpendicularly from the metal surface which causes a half-wavelength to occur in spectrum analysis. The magneto-hydro-dynamic theory analysis shows that the change of electrothermal instabilities is caused dominantly by the modulation of current density flowing around the periodical structure.

Experimental investigation of plasma cloud scattering initiated by an accelerated electron beam

The parameters for the charged particle flow of a plasma cloud (PC) explosion initiated by an electron beam have been measured. Two types of PCs were investigated: 1) PC with a free boundary and 2) PC restricted by electrodes. It was established that the basic particle flow parameters for such a plasma explosion coincide in common with the parameters of accelerated particle flow of different types of vacuum discharges. Energy spectra have several maxima. There is a dependence of ion energy on the ion charge state. PC is scattered in a wide spatial angle. The geometry of the propagation volume affects the energy spectrum of ions.

Mapping nanoscale absorption of femtosecond laser pulses using plasma explosion imaging.

We make direct observations of localized light absorption in a single nanostructure irradiated by a strong femtosecond laser field, by developing and applying a technique that we refer to as plasma explosion imaging. By imaging the photoion momentum distribution resulting from plasma formation in a laser-irradiated nanostructure, we map the spatial location of the highly localized plasma and thereby image the nanoscale light absorption. Our method probes individual, isolated nanoparticles in vacuum, which allows us to observe how small variations in the composition, shape, and orientation of the nanostructures lead to vastly different light absorption. Here, we study four different nanoparticle samples with overall dimensions of ∼100 nm and find that each sample exhibits distinct light absorption mechanisms despite their similar size. Specifically, we observe subwavelength focusing in single NaCl crystals, symmetric absorption in TiO2 aggregates, surface enhancement in dielectric particles containing a single gold nanoparticle, and interparticle hot spots in dielectric particles containing multiple smaller gold nanoparticles. These observations demonstrate how plasma explosion imaging directly reveals the diverse ways in which nanoparticles respond to strong laser fields, a process that is notoriously challenging to model because of the rapid evolution of materials properties that takes place on the femtosecond time scale as a solid nanostructure is transformed into a dense plasma.

Modeling the dynamics of a high specific energy plasma bulge in the upper atmosphere: 1. Physics of the processes and numerical simulation of the early stage of plasma bulge expansion and interaction with the ionosphere and geomagnetic field: A review

The physicomathematical features of the plasma explosion region dynamics at altitudes higher than 100 km at the early stage of its development, which culminates in the transfer of a considerable portion of the initial plasma energy into the environment, are discussed in the first part of the work. The radiation gas dynamic, inertial, and shock stages of the disturbed region development are calculated.

BiotecVisions 2012, February

BiotecVisions 2012, February

Minimally invasive non‐thermal laser technology using laser‐induced optical breakdown for skin rejuvenation

We describe a novel, minimally invasive laser technology for skin rejuvenation by creating isolated microscopic lesions within tissue below the epidermis using laser induced optical breakdown. Using an in-house built prototype device, tightly focused near-infrared laser pulses are used to create optical breakdown in the dermis while leaving the epidermis intact, resulting in lesions due to cavitation and plasma explosion. This stimulates a healing response and consequently skin remodelling, resulting in skin rejuvenation effects. Analysis of ex-vivo and in-vivo treated human skin samples successfully demonstrated the safety and effectiveness of the microscopic lesion creation inside the dermis. Treatments led to mild side effects that can be controlled by small optimizations of the optical skin contact and treatment depth within the skin. The histological results from a limited panel test performed on five test volunteers show evidence of microscopic lesion creation and new collagen formation at the sites of the optical breakdown. This potentially introduces a safe, breakthrough treatment procedure for skin rejuvenation without damaging the epidermis with no or little social down-time and with efficacy comparable to conventional fractional ablative techniques. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Special features of formation of defects in explosion welding of two-layer large plates

Continuity check results of two-layer plates from several consignments are given. A shock pinched plasma generator and explosion welding technique on its base are developed, application of which allowed for excluding discontinuity formation at the beginning of welding and for eliminating stabilization area of joint efficiency and wave structure.

Exposure Assessment of Silver Nanomaterials in Workplaces

PP-29-167 Background/Aims: Recently, numerous processes for the production of nanomaterials have been developed. With the increasing use of engineered nanomaterials, it is expected to increase the occupational exposures to nanomaterials in the workplace. The exposed nanomaterials may enter and accumulate in our body, potentially causing injury or death to humans. Especially, workers can be directly exposed to nanomaterials for a long time. Methods: However, the researches on the exposure assessment of nanomaterials to human and environment are just beginning step. Therefore, exposure assessment based on the real-time monitoring of exposed nanoparticle is one of the critical issues for EHS (environment, health, and safety). Results: In this study, exposure assessment of silver nanoparticles (AgNPs) in the workplaces was performed. AgNPs was generally synthesized by sol-gel chemistry (colloid AgNPs) or plasma explosion method (powder AgNPs). Sampling of exposed nanomaterials was conducted with SMPS (Scanning Mobility Particle Sizer) and auto-sampler, ESP (Electrostatic Precipitator). The collected samples were analyzed by TEM (Transmission Electron Microscope) for size, morphology, and agglomeration conditions. Conclusion: In the results, the nanoparticle concentrations in the air during the processing step were higher than those of normal conditions.

X-Ray Backlighting of Developments of $X$-pinches and Wire-Array $Z$-pinches Using an $X$-pinch

A pulsed-power generator (PPG-I) with a current of 400 kA in amplitude and 100 ns in pulsewidth was constructed. The development of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">X</i> -pinches and the early stages of wire-array <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Z</i> -pinches were investigated by X-ray backlighting using the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">X</i> -pinch driven by PPG-I as X-ray source. The plasma explosion and implosion near the cross point of the X-shape wires can be clearly seen from a series of backlighting images taken at different times of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">X</i> -pinch discharge. To study the early behavior of the plasma in wire-array <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Z</i> -pinches, an <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">X</i> -pinch installed in the place of a current-return rod was used as the X-ray source to backlight a wire-array <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Z</i> -pinch installed in the center between the anode and the cathode. The plasma formation, the interwire plasma merging, and the instabilities were also clearly observed, which can provide a better understanding of the physics of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Z</i> -pinches and the basic experimental data to validate simulation models.

Dynamic evolution of the short laser-induced inclusion plasma explosion

When femtosecond laser irradiates materials, plasma with high electronic temperature and low lattice temperature will form due to very high laser power density. This plasma with high electronic temperature cannot exist stably, and it has a trend to expand. If the plasma inclusion is initialized, it will be confined by outer layers when it expands. In this paper, the energy conservation rule was used to analyze the mechanical evolution of inclusion of plasma explosion. An inequality for judging whether the film can be damaged has been deduced.

The dynamic process of thin films damage induced by femtosecond laser

A dynamic model of plasma explosion is put forward. The inertia factor is considered daring plasma expansion, and the dynamic simulation is carried out. The dynamic mechanism of film damage induced by plasma blast is discussed.

Initial formation process of laser-induced plasma shock wave in air

The initial formation process of laser-induced plasma shock wave in air during laser damage process has been studied experimentally with a well-designed optical fiber sensor based on detecting beam deflection. The experimental results indicate that the formation of the laser-induced plasma shock wave is the result of the overlap of vapor- and explosion-shock waves. The plasma explosion shock wave, which generates behind the vapor shock wave but has a higher speed, catches up with the vapor shock wave and overlaps it at a certain distance, giving the result of a strong shock wave in air. The distance is about 3 mm when a 170 mJ laser at 1.06 μm with 30 ns duration irradiates an aluminum target in air.

Evaluation of Stored Energy in Ultrafine Aluminum Powder Produced by Plasma Explosion

Ultrae ne aluminum powder produced by plasma explosion (ALEX) exhibits burn behavior unlike that of ordinary aluminum powders. Others have previously suggested that the source of this unique behavior might be stored internal energy. The objective of this study is to evaluate theoretically the feasibility of energy being stored in ALEX as a result of work performed by means of the compression of the liquid portion of an ALEX particle by its shrinking solid shell during rapid solidie cation of the particle. A theoretical model of this process of energy storage was developed. This model was then formulated and numerically solved on a computer for a variety of conditions. Results show that the postulated mechanism results in measurable stored energy for only unrealistically high cooling rates. It is concluded that, although the postulated mechanism could store energy, the amount of energy stored is realistically negligible. This theoretical e nding is in agreement with recent experiments that show no observable stored energy in ALEX particles. Nomenclature A = surface area, m 2 B = bulk modulus, N/m 2 Cp = specie c heat, J/kg ¢K D = diameter, m Est = thermal energy stored during solidie cation, J H f = latent heat of fusion, J/kg h = heat transfer coefe cient, W/m 2 ¢K k = thermal conductivity, W/m ¢K m = mass, kg N = surface node P = pressure, Pa r = radius,m T = temperature, K Ti = initial temperature, K V = volume, m 3 W = work, J ¯ = thermal coefe cient of expansion, 1/K 1t = time-step increment, s Ω = density, kg/m 3

Comparison of Thermal Behavior of Regular and Ultra-fine Aluminum Powders (Alex) Made from Plasma Explosion Process

Alex powder (an ultra-fine aluminum powder produced by the plasma-explosion process) has been shown to be a very effective burning rate enhancer for solid propellants and fuels. The objective of this research is to investigate the mechanisms responsible for the beneficial effect of Alex. A TGA and DTA were employed to examine the thermal bahavior of Alex and regular aluminum particles in different gases. An environmental scanning electron microscope (ESEM) was utilized to study the particle surface bahavior when samples were heated in air and nitrogen. A transmission electron microscope (TEM) was employed for examining the microstructure of Alex particles. Alex powder was demonstrated in TGA and DTA experiments to behave very differently from the regular aluminum in air, oxygen and nitrogen. Rapid weight gain of Alex particles in air and nitrogen environment occurred around 548°C and 700°C, respectively. The low-temperature reaction in air corresponds to an oxidation reaction. Comparing DTA traces of Alex and regular aluminum in air, it was found that oxidation of Alex particles occurs at a lower temperature with a higher degree of reaction. This is believed to be mainly due to the higher reactivity associated with greater surface area of the Alex particles. In the comparison of DTA traces of Alex and regular aluminum in nitrogen, the rapid nitridation reaction of Alex particles occurs at temperature around 680°C and proceeds to near completion.

The surface fireball effect caused by the Coulomb particles in laser-generated plasmas: the plasma explosion regime

Laser-material processing in the regime of plasma explosion in vacuum and in pressurized (reactive) gaseous atmospheres is a new emerging technology. The characteristics are considered of the explosion of a “colloidal” laser-generated plasma, i.e. a plasma containing Coulomb particles, and their effects on a titanium surface. Being very hot ( T = 3200 K) they produce fireball effects and leave a present pattern on the metal surface, which reveals their spatial order in the plasma during the pulse, and in the regime of adiabatic expansion after pulse termination (S Lugomer and G Bitelli, Vacuum (in press)). Among all the cases studied (Ta in N 2; Ta in O 2; Mo in N 2; Mo in O 2; Ti in N 2) only the system Ti in O 2 reveals the laser-plasma explosion. Coulomb particles generate a very specific type of pattern whose morphological and statistical characteristics are described in this paper. A posteriori analysis of a Ti surface after a plasma explosion revealed an elliptical spot with the flower-like (wavy) envelope characteristic of the Richtmyer-Meshkov instability. The inner side of the surface spot indicated a dominance of the jetting phenomena. It is shown that the jetting pattern is a multifractal pattern of the Cantor type with a spatial distribution of jetting, which can be expressed as the ratio series: 3 25 ; 3 23 ; 3 20 ; 1 5 ; 1 3 ; 1 2 ; 3 5 ;, 3 4 ; 3 3 . The particle spin and the average periodicity Δ of jetting over the whole spot, appear to be the universal properties connected with explosion of laser-generated “colloidal” plasma, not reported previously. Molten titanium in the central zone and in the jets on the periphery oxidizes quickly and transforms into an amorphous glassy phase after pulse termination.

Modification of the surface properties of Ti by explosion of laser-plasma containing Coulomb particles

This paper continues the study of the effects on a Ti surface caused by the explosion of a laser-plasma containing Coulomb particles. (Generation of such a system and particle self-organization in laser-material interaction (L-M I), was described in: S Lugomer and G Bitelli, Vacuum, 47 , 13 (1996). The laser-plasma explosion in an O 2 atmosphere, and the characteristic surface morphology by accelerated Coulomb particles, was reported in S Lugomer and G Bitelli, Vacuum, 47 , 271 (1996).) Modification of the surface properties of titanium by the Coulomb particles in the exploding plasma was studied by Vickers microhardness tests, X-ray diffraction and Raman backscattering. A large jump of microhardness from the background value of 288 Kp/mm 2 to ≈ 700–7200 Kp/mm 2 was observed at the places of gassy Ti-oxide; the jump is smaller (to ≈450–700 Kp/mm 2) on the other oxidized zones. Finally, a decrease of microhardness on the pure Tisurface occurs, because of plasma thermal effects (annihilation of dislocations in the surface zone). Raman backscattering studies have shown the existence of a partially crystalline Ti-oxide and also an amorphous (glassy) one. The contribution of the crystalline phases, anatase and the rutile (the low- and the high-temperature phases), changes with the number of laser pulses, i.e. the low-temperature phase is transferred into the high-temperature one, by repetitive laser pulsing. The broad background band (Bose peak) was interpreted on the basis of the fraction model using the Yakubo's relation for fitting the real spectra. The phonon-fracton crossover frequency ω CO1 , was found to be sensitive to the O 2 pressure for P < 5 atm, and quite insensitive for P ≥ 5 atm. Correlation of the results of Raman backscattering and the X-ray diffraction, indicates that the laser plasma explosion in O 2 generates the glassy matrix of Ti-oxide, into which the crystallites of TiO 2 (the anatase and the rutile phases, of size ranging from <10 A ̊ to tens of nm) are embedded.