Shock Wave Heating Research Articles

Laser induced fast ignition made realistic by relativistic velocities-dream or reality?

Due to the recent developments in high power lasers it is suggested to accelerate a micro-foil by the laser pressure to relativistic velocities. The time dependent velocity of this micro-foil is calculated analytically for pulsed constant laser intensity. The accelerated foil collides with a target creating a shock wave on impact. The shock wave parameters are calculated within the context of relativistic fluid dynamics.It is suggested to use the energy of the relativistic micro-foil to ignite a pre-compressed target with a density relevant for fusion ignition. The equations are written and solved for the collision between the micro-foil and the very dense target. The criteria for shock wave ignition and heat wave ignition are used to show that one needs significantly less laser energy for heat wave ignition.The present scheme shows that nuclear fast ignition by micro-foil impact could be attained in the near future with lasers that are currently under construction.

Solution of a kinetic equation for diatomic gas with the use of differential scattering cross sections computed by the method of classical trajectories

A collision integral is constructed taking into account the rotational degrees of freedom of the gas molecules. Its truncation error is shown to be second order in the rotational velocity mesh size. In the solution of the kinetic equation, the resulting collision integral is directly computed using a projection method. Preliminarily, the differential scattering cross sections of nitrogen molecules are computed by applying the method of classical trajectories. The resulting cross section values are tabulated in multimillion data arrays. The one-dimensional problems of shock wave structure and heat transfer between two plates are computed as tests, and the results are compared with experimental data. The convergence of the results with decreasing rotational velocity mesh size is analyzed.

Histological and Biochemical Analysis of Mechanical and Thermal Bioeffects in Boiling Histotripsy Lesions Induced by High Intensity Focused Ultrasound

Recent studies have shown that shockwave heating and millisecond boiling in high-intensity focused ultrasound fields can result in mechanical fractionation or emulsification of tissue, termed boiling histotripsy. Visual observations of the change in color and contents indicated that the degree of thermal damage in the emulsified lesions can be controlled by varying the parameters of the exposure. The goal of this work was to examine thermal and mechanical effects in boiling histotripsy lesions using histologic and biochemical analysis. The lesions were induced in ex vivo bovine heart and liver using a 2-MHz single-element transducer operating at duty factors of 0.005–0.01, pulse durations of 5–500 ms and in situ shock amplitude of 73 MPa. Mechanical and thermal damage to tissue was evaluated histologically using conventional staining techniques (hematoxylin and eosin, and nicotinamide adenine dinucleotide-diaphorase). Thermal effects were quantified by measuring denaturation of salt soluble proteins in the treated region. According to histologic analysis, the lesions that visually appeared as a liquid contained no cellular structures larger than a cell nucleus and had a sharp border of one to two cells. Both histologic and protein analysis showed that lesions obtained with short pulses (<10 ms) did not contain any thermal damage. Increasing the pulse duration resulted in an increase in thermal damage. However, both protein analysis and nicotinamide adenine dinucleotide-diaphorase staining showed less denaturation than visually observed as whitening of tissue. The number of high-intensity focused ultrasound pulses delivered per exposure did not change the lesion shape or the degree of thermal denaturation, whereas the size of the lesion showed a saturating behavior suggesting optimal exposure duration. This study confirmed that boiling histotripsy offers an effective, predictable way to non-invasively fractionate tissue into sub-cellular fragments with or without inducing thermal damage.

Experimental Study of Ignition over Impact-Driven Supersonic Liquid Fuel Jet

This study experimentally investigates the mechanism of the ignition of the supersonic liquid fuel jet by the visualization. N-Hexadecane having the cetane number of 100 was used as a liquid for the jet in order to enhance the ignition potential of the liquid fuel jet. Moreover, the heat column and the high intensity CO2 laser were applied to initiate the ignition. The ignition over the liquid fuel jet was visualized by a high-speed digital video camera with a shadowgraph system. From the shadowgraph images, the autoignition or ignition of the supersonic liquid fuel jet, at the velocity of 1,186 m/s which is a Mach number relative to the air of 3.41, did not take place. The ignition still did not occur, even though the heat column or the high intensity CO2 laser was alone applied. The attempt to initiate the ignition over the liquid fuel jet was achieved by applying both the heat column and the high intensity CO2 laser. Observing the signs of luminous spots or flames in the shadowgraph would readily indicate the presence of ignitions. The mechanism of the ignition and combustion over the liquid fuel jet was clearly clarified. Moreover, it was found that the ignition over the supersonic liquid fuel jet in this study was rather the force ignition than being the auto-ignition induced by shock wave heating.

Controlled tissue emulsification produced by high intensity focused ultrasound shock waves and millisecond boiling

In high intensity focused ultrasound (HIFU) applications, tissue may be thermally necrosed by heating, emulsified by cavitation, or, as was recently discovered, emulsified using repetitive millisecond boiling caused by shock wave heating. Here, this last approach was further investigated. Experiments were performed in transparent gels and ex vivo bovine heart tissue using 1, 2, and 3 MHz focused transducers and different pulsing schemes in which the pressure, duty factor, and pulse duration were varied. A previously developed derating procedure to determine in situ shock amplitudes and the time-to-boil was refined. Treatments were monitored using B-mode ultrasound. Both inertial cavitation and boiling were observed during exposures, but emulsification occurred only when shocks and boiling were present. Emulsified lesions without thermal denaturation were produced with shock amplitudes sufficient to induce boiling in less than 20 ms, duty factors of less than 0.02, and pulse lengths shorter than 30 ms. Higher duty factors or longer pulses produced varying degrees of thermal denaturation combined with mechanical emulsification. Larger lesions were obtained using lower ultrasound frequencies. The results show that shock wave heating and millisecond boiling is an effective and reliable way to emulsify tissue while monitoring the treatment with ultrasound.

Transient Behavior of Magnetohydrodynamic Power-Generating Plasma

We present the structure of a nonequilibrium cesium-seeded argon (Ar-Cs) plasma in a closed-cycle magnetohydrodynamic (MHD) electrical power generator driven by a shock-tunnel facility. The transitional behavior from an inflow phase to an MHD phase is visualized. In the inflow phase, the high-temperature Ar-Cs gas produced by shock-wave heating flows in a supersonic channel. In the MHD phase, the plasma is self-organized by MHD effects. At the same time, the enthalpy of a flow is extracted in the form of electricity via the MHD effects.

A mechanism of tissue emulsification by high intensity focused ultrasound

High intensity focused ultrasound (HIFU) has been shown to emulsify tissue in histotripsy created by cavitation clouds and millisecond boiling produced by shock wave heating; however, the mechanism by which millimeter-sized boiling bubbles or cavitation bubble clouds emulsify tissue into submicron-sized pieces is not well understood. Here, we experimentally test the hypothesis that acoustic atomization occurs and a miniature acoustic fountain forms (due to radiation force) at the edge of the millimeter-sized boiling bubble. Through high-speed photography, we observed the violent removal of bovine/porcine liver fragments upon focusing a 2-MHz transducer of 70 MPa peak positive and 15 MPa peak negative pressures at the tissue–air interface. Velocity of the fountain projectiles ranged from 5 to 15 m/s. When the focal amplitudes were reduced to 15 MPa peak positive and 7 MPa peak negative pressures, atomization occurred intermittently. The fountain projectiles were collected and examined histologically using H&amp;E and NADH--diaphorase stains. Results show fragments ranging from tens of microns down to submicron in size. The larger fragments contain distinct tissue aggregates with intact cells and the small particles are cell fragments with few to no intact nuclei. [Work supported by NIH DK43881, DK070618, EB007643, DK007742, and NSBRI through NASA NCC 9--58.]

A method of mechanical emulsification in a bulk tissue using shock wave heating and millisecond boiling.

Recent studies in high intensity focused ultrasound (HIFU) have shown significant interest in generating purely mechanical damage of tissue without thermal coagulation. Here, an approach using millisecond bursts of ultrasound shock waves and repeated localized boiling is presented. In HIFU fields, nonlinear propagation effects lead to formation of shocks only in a small focal region. Significant enhancement of heating due to absorption at the shocks leads to boiling temperatures in tissue in milliseconds as calculated based on weak shock theory. The heated and potentially necrotized region of tissue is small compared to the volume occupied by the mm-sized boiling bubble it creates. If the HIFU pulse is only slightly longer than the time-to-boil, thermal injury is negligible compared to the mechanical injury caused by the exploding boiling bubble and its further interaction with shocks. Experiments performed in transparent gels and various ex vivo and in vivo tissues have confirmed the effectiveness of this emulsification method. In addition, since mm-sized boiling bubbles are highly echogenic, tissue emulsification can be easily monitored in real-time using B-mode ultrasound imaging. [Work supported by NIH EB007643, RFBR 09-02-01530, and NSBRI through NASA NCC 9-58].

Miniature acoustic fountain mechanism for tissue emulsification during millisecond boiling in high intensity focused ultrasound fields.

Feasibility of soft tissue emulsification using shock wave heating and millisecond boiling induced by high intensity focused ultrasound was demonstrated recently. However, the mechanism by which the bubbles emulsify tissue is not well understood. High-speed photography of such exposures in transparent gel phantoms shows a milimeter-sized boiling bubble, and histological analysis in tissue samples reveals sub-micron-sized fragments. Here, a novel mechanism of tissue emulsification by the formation of a miniature acoustic fountain within the boiling bubble is tested experimentally using a 2 MHz transducer generating up to 70 MPa positive and 15 MPa negative peak pressures at the focus. The focus was positioned at or 1–2 mm off the plane interface between air and various materials including degassed water, transparent gel, thin sliced muscle tissue phantom, and ex-vivo tissue. Pulsing schemes with duty factors 0.001–0.1, and pulse durations 0.05–500 ms were used. Violent removal of micron-sized fragments and substantial displacement of the phantom surface were observed through high-speed filming. At the end of each exposure, the resulting erosion of the phantom surface and subsurface area was photographed and related to the exposure parameters. Work supported by NIH (DK43881, DK070618, EB007643, and DK007742) and NSBRI through NASA NCC 9-58.

Histological and biochemical analysis of emulsified lesions in tissue induced by high intensity focused ultrasound.

As recently shown, shock wave heating and millisecond boiling can be used to obtain mechanical emulsification of tissue with or without evident thermal damage, which can be controlled by varying the parameters of the high intensity focused ultrasound exposure. The goal of this work was to examine these bioeffects using histological and biochemical analysis. Lesions were created in ex vivo bovine heart and liver using a 2-MHz transducer and pulsing scheme with 71 MPa in situ shock amplitude, 0.01 duty factor, and 5–500 ms pulse duration. Mechanical tissue damage and viability of cells in the lesions were evaluated histologically using conventional staining techniques (H&amp;E and NADH-diaphorase). Thermal effects were quantified by measuring denaturation of salt soluble proteins in the treated area and confirmed by histology. By visual observation, the liquefied lesions obtained with shorter pulses (&amp;lt; 15 ms) did not show any thermal damage that correlated well with the results of both histology and protein analysis. Increasing the pulse duration resulted in an increase in thermal damage; both protein analysis and NADH-diaphorase staining showed denaturation that was visually observed as whitening of the lesion content. [Work supported by NSBRI through NASA NCC 9-58, NIH EB007643 and DK007742.]

FORMATION OF COSMIC CRYSTALS IN HIGHLY SUPERSATURATED SILICATE VAPOR PRODUCED BY PLANETESIMAL BOW SHOCKS

Several lines of evidence suggest that fine silicate crystals observed in primitive meteorite and interplanetary dust particles (IDPs) nucleated in a supersaturated silicate vapor followed by crystalline growth. We investigated evaporation of $\mu$m-sized silicate particles heated by a bow shock produced by a planetesimal orbiting in the gas in the early solar nebula and condensation of crystalline silicate from the vapor thus produced. Our numerical simulation of shock-wave heating showed that these {\mu}m-sized particles evaporated almost completely when the bow shock is strong enough to cause melting of chondrule precursor dust particles. We found that the silicate vapor cools very rapidly with expansion into the ambient unshocked nebular region; the cooling rate is estimated, for instance, to be as high as 2000 K s$^{-1}$ for a vapor heated by a bow shock associated with a planetesimal of radius 1 km. The rapid cooling of the vapor leads to nonequilibrium gas-phase condensation of dust at temperatures much lower than those expected from the equilibrium condensation. It was found that the condensation temperatures are lower by a few hundred K or more than the equilibrium temperatures. This explains the results of the recent experimental studies of condensation from a silicate vapor that condensation in such large supercooling reproduces morphologies similar to those of silicate crystals found in meteorites. Our results suggest strongly that the planetesimal bow shock is one of the plausible sites for formation of not only chondrules but also other cosmic crystals in the early solar system.

Finite Rate Chemistry Large-Eddy Simulation of Self-Ignition in Supersonic Combustion Ramjet

In this study, large-eddy simulation is used to analyze supersonic flow, mixing, and combustion in a supersonic combustor equipped with a two-stage fuel injector strut. The present study focuses on mixing, ignition, and flame stabilization and the degree of detail required by the reaction mechanism in the large-eddy simulation model framework. An explicit large-eddy simulation model, using a mixed subgrid model and a partially stirred reactor turbulence-chemistry interaction model, is used in an unstructured finite volume setting. The model, and its components, has been carefully validated in a large number of other studies. To bestow further validation and to provide supplementary information about the physics of mixing and supersonic combustion, experimental data from the National Aerospace Laboratory of Japan's supersonic combustor, equipped with the two-stage strut injector and connected to ONERA's vitiation air heater, are employed. The large-eddy simulation predictions are compared with the experimental centerline wall pressure distribution and the planar laser-induced fluorescence imaging of hydroxide-ion radicals distributions in several cross sections of the combustor, showing excellent qualitative and quantitative agreements. The large-eddy simulation results are furthermore used to elucidate the complicated flow, mixing, and combustion physics imposed by the multi-injector two-stage injector strut. The importance of the combustion chemistry appears weaker than expected but with the one-step mechanism resulting in a too early ignition (caused by local shock wave heating) and a more stable flame, as compared with the more detailed two- and seven-step mechanisms.

Giant impact stratification of the Martian core

We investigate the direct thermal effects of giant impacts on the Martian core and its dynamo. Shock wave heating of Mars is calculated in terms of the impact velocity and the final basin size. Although much of the shock wave heat is deposited in the mantle, shock heating from a giant impact produces non‐uniform temperatures in the core, leading to an overturn event and stable thermal stratification in the liquid core. Numerical dynamos with core heating from polar and equatorial impacts show that the overturn and stratification quickly destroys a pre‐existing core dynamo, within ten thousand years. Energy considerations reveal that both the stratification and the time required for removal of the stratification increase with impact size. Our calculations indicate that several tens to over one hundred million years are required for removal of core stratification following a giant impact.

Onset of Material Alterations Due to Laser-Induced Plasma Exposure in Nanofilms Deposited on Photomasks

Damage-free removal of sub-100 nm particles from photomasks with deposited nanofilms is a challenge in lithography. Laser-induced plasma (LIP) is an emerging noncontact, chemical-free, dry, and selective nanoparticle removal technique. Investigation of the onset of material alterations on bonded nanofilms for optimizing LIP particle removal process is the objective of this paper. Shockwave thermomechanical excitation and radiation heating from the plasma core are major potential sources of damage. Computational analyses reported here indicate radiation heating as the chief damage source. Damage thresholds for the critical nanofilm surface temperature rise and radial stress component have been identified for a given nanosecond pulsed laser.

AFM study on surface nanotopography of matrix olivines in Allende carbonaceous chondrite

By means of nanoscale surface observation, we have proposed a new approach for investigating fine crystals of cosmic materials to reveal their origin and growth conditions. Several different morphologies of polyhedral fine olivines with faceted faces have been found in Allende carbonaceous chondrite (4.5 byr in geochronological age). In the present work, molecular level topography of the faceted matrix olivine by Atomic Force Microscopy (AFM) has successfully been performed. The matrix olivine found to have preserved growth step pattern on its surface even though quite long time has passed since they formed in the early Solar System. The surface pattern suggests that the faceted matrix olivine could have been condensed from the gas phase, and possibly that these olivine crystals had continued to grow under a rapid cooling condition (0.1–1 K s −1). The estimated cooling rate agrees well with predictions based on hypothetical rapid heating and cooling events such as shock wave heating.

Compound chondrule formation in the shock-wave heating model: Three-dimensional hydrodynamics simulation of the disruption of a partially-molten dust particle

We carried out three-dimensional hydrodynamics simulations of the disruption of a partially-molten dust particle exposed to high-speed gas flow to examine the compound chondrule formation due to mutual collisions between the fragments (fragment-collision model; [Miura, H., Yasuda, S., Nakamoto, T., 2008a. Icarus194, 811–821]). In the shock-wave heating model, which is one of the most plausible models for chondrule formation, the gas friction heats and melts the surface of the cm-sized dust particle (parent particle) and then the strong gas ram pressure causes the disruption of the molten surface layer. The hydrodynamics simulation shows details of the disruptive motion of the molten surface, production of many fragments and their trajectories parting from the parent particle, and mutual collisions among them. In our simulation, we identified 32 isolated fragments extracted from the parent particle. The size distribution of the fragments was similar to that obtained from the aerodynamic experiment in which a liquid layer was attached to a solid core and it was exposed to a gas flow. We detected 12 collisions between the fragments, which may result in the compound chondrule formation. We also analyzed the paths of all the fragments in detail and found the importance of the shadow effect in which a fragment extracted later blocks the gas flow toward a fragment extracted earlier. We examined the collision velocity and impact parameter of each collision and found that 11 collisions should result in coalescence. It means that the ratio of coalescent bodies to single bodies formed in this disruption of a parent particle is R coa = 11 / ( 32 - 11 ) = 0.52 . We concluded that compound chondrule formation can occur just after the disruption of a cm-sized molten dust particle in shock-wave heating.

Al 1 s - 2 p absorption spectroscopy of shock-wave heating and compression in laser-driven planar foil

Time-resolved Al 1s-2p absorption spectroscopy is used to diagnose direct-drive, shock-wave heating and compression of planar targets having nearly Fermi-degenerate plasma conditions (Te∼10–40 eV, ρ∼3–11 g/cm3) on the OMEGA Laser System [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)]. A planar plastic foil with a buried Al tracer layer was irradiated with peak intensities of 1014–1015 W/cm2 and probed with the pseudocontinuum M-band emission from a point-source Sm backlighter in the range of 1.4–1.7 keV. The laser ablation process launches 10–70 Mbar shock waves into the CH/Al/CH target. The Al 1s-2p absorption spectra were analyzed using the atomic physic code PRISMSPECT to infer Te and ρ in the Al layer, assuming uniform plasma conditions during shock-wave heating, and to determine when the heat front penetrated the Al layer. The drive foils were simulated with the one-dimensional hydrodynamics code LILAC using a flux-limited (f=0.06 and f=0.1) and nonlocal thermal-transport model [V. N. Goncharov et al., Phys. Plasmas 13, 012702 (2006)]. The predictions of simulated shock-wave heating and the timing of heat-front penetration are compared to the observations. The experimental results for a wide variety of laser-drive conditions and buried depths have shown that the LILAC predictions using f=0.06 and the nonlocal model accurately model the shock-wave heating and timing of the heat-front penetration while the shock is transiting the target. The observed discrepancy between the measured and simulated shock-wave heating at late times of the drive can be explained by the reduced radiative heating due to lateral heat flow in the corona.

Size distributions of chondrules and dispersed droplets caused by liquid breakup: An application to shock wave conditions in the solar nebula

We present the results of an aerodynamic liquid dispersion experiment using initially molten silicate samples. We investigate the threshold of breakup and the size distribution of dispersed droplets. The breakup threshold is consistent with the previous experiments using water and a mixture of water and glycerol. Also, we confirm the previous results that the size distributions of dispersed droplets are represented by an exponential form and that the characteristic size of dispersed droplets is related to the dynamic pressure of high-velocity gas flow. The size distribution has a similar form to that of chondrules, though the experiment is not exactly corresponding to the shock heating models for chondrule formation that consider solid precursors which are molten by the shocks. The experimental results indicate that, if liquid chondrule-precursors were dispersed by high-velocity flow, the dynamic pressure of the flow is ∼ 10 kPa . A chondrule formation condition in a shock-wave heating model suggests that this pressure can be realized at the regions within ∼ 1 AU in the minimum solar-nebula mass models. However, if the nebula had a larger mass and gravitational instabilities occurred, this pressure may be realized in the spiral arms at 2–3 AU and chondrules may be formed in asteroid belt.

Origin of three-dimensional shapes of chondrulesI. Hydrodynamics simulations of rotating droplet exposed to high-velocity rarefied gas flow

Abstract The origin of three-dimensional shapes of chondrules is an important information to identify their formation mechanism in the early solar nebula. The measurement of their shapes by using X-ray computed topography suggested that they are usually close to perfect spheres, however, some of them have rugby-ball-like (prolate) shapes [Tsuchiyama, A., Shigeyoshi, R., Kawabata, T., Nakano, T., Uesugi, K., Shirono, S., 2003. Lunar Planet. Sci. 34, 1271–1272]. We considered that the prolate shapes reflect the deformations of chondrule precursor dust particles when they are heated and melted in the high velocity gas flow. In order to reveal the origin of chondrule shapes, we carried out the three-dimensional hydrodynamics simulations of a rotating molten chondrule exposed to the gas flow in the framework of the shock-wave heating model for chondrule formation. We adopted the gas ram pressure acting on the chondrule surface of p fm = 10 4 dyn cm −2 in a typical shock wave. Considering that the chondrule precursor dust particle has an irregular shape before melting, the ram pressure causes a net torque to rotate the particle. The estimated angular velocity is ω f = 140 rad s −1 for the precursor radius of r 0 = 1 mm , though it has a different value depending on the irregularity of the shape. In addition, the rotation axis is likely to be perpendicular to the direction of the gas flow. Our calculations showed that the rotating molten chondrule elongates along the rotation axis, in contrast, shrinks perpendicularly to it. It is a prolate shape. The reason why the molten chondrule is deformed to a prolate shape was clearly discussed. Our study gives a complementary constraint for chondrule formation mechanisms, comparing with conventional chemical analyses and dynamic crystallization experiments that have mainly constrained the thermal evolutions of chondrules.

Fragment-collision model for compound chondrule formation: Estimation of collision probability

We propose a new scenario for compound chondrule formation named as “fragment-collision model,” in the framework of the shock-wave heating model. A molten cm-sized dust particle (parent) is disrupted in the high-velocity gas flow. The extracted fragments (ejectors) are scattered behind the parent and the mutual collisions between them will occur. We modeled the disruption event by analytic considerations in order to estimate the probability of the mutual collisions assuming that all ejectors have the same radius. In the typical case, the molten thin ( ∼ 1 mm ) layer of the parent surface will be stripped by the gas flow. The stripped layer is divided into about 200 molten ejectors (assuming that the radius of ejectors is 300 μm) and then they are blown away by the gas flow in a short period of time ( ∼ 0.01 s ). The stripped layer is leaving from the parent with the velocity of ∼ 4 cm s −1 depending on the viscosity, and we assumed that the extracted ejectors have a random velocity Δ v of the same order of magnitude. Using above values, we can estimate the number density of ejectors behind the parent as n e ∼ 800 cm −3 . These ejectors occupy ∼9% of the space behind the parent in volume. Considering that the collision rate (number of collisions per unit time experienced by an ejector) is given by R coll = σ coll n e Δ v , where σ coll is the cross-section of collision [e.g., Gooding, J.K., Keil, K., 1981. Meteoritics 16, 17–43], we obtain R coll ∼ 36 collisions / s by substituting above values. Since most collisions occur within the short duration ( ∼ 0.01 s ) before the ejectors are blown away, we obtain the collision probability of P coll ∼ 0.36 , which is the probability of collisions experienced by an ejector in one disruption event. The estimated collision probability is about one order of magnitude larger than the observed fraction of compound chondrules. In addition, the model predictions are qualitatively consistent with other observational data (oxygen isotopic composition, textural types, and size ratios of constituents). Based on these results, we concluded that this new model can be one of the strongest candidates for the compound chondrule formation. It should be noted that all collisions do not necessarily lead to the compound chondrule formation. The formation efficiency and the future works which should be investigated in the forthcoming paper are also discussed.