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Polyoxymethylene (POM) has been widely studied as a laser propulsion propellant paired to CO2 laser radiation. POM is a good test case for studying ablation properties of polymer materials, and within limits, for study of general trends in laser ablation‐induced impulse. Despite many studies, there is no general understanding of POM ablation that takes into account the ambient pressure, spot area, fluence, and effects from confinement and combustion. This paper reviews and synthesizes CO2 laser ablation propulsion research using POM targets. Necessary directions for future study are indicated to address incomplete regions of the various parameter spaces. Literature data is compared in terms of propulsion parameters such as momentum coupling coefficient and specific impulse, within a range of fluences from about 1–500 J/cm2, ambient pressures from about 10−2–105 Pa, and laser spot areas from about 0.01–10 cm2.

Laser Ablation Propulsion is a broad field with a wide range of applications. We review the 30‐year history of laser ablation propulsion from the transition from earlier pure photon propulsion concepts of Oberth and Sanger through Kantrowitz’s original laser ablation propulsion idea to the development of air‐breathing “Lightcraft” and advanced spacecraft propulsion engines. The polymers POM and GAP have played an important role in experiments and liquid ablation fuels show great promise. Some applications use a laser system which is distant from the propelled object, for example, on another spacecraft, the Earth or a planet. Others use a laser that is part of the spacecraft propulsion system on the spacecraft. Propulsion is produced when an intense laser beam strikes a condensed matter surface and produces a vapor or plasma jet. The advantages of this idea are that exhaust velocity of the propulsion engine covers a broader range than is available from chemistry, that it can be varied to meet the instantaneous demands of the particular mission, and that practical realizations give lower mass and greater simplicity for a payload delivery system. We review the underlying theory, buttressed by extensive experimental data. The primary problem in laser space propulsion theory has been the absence of a way to predict thrust and specific impulse over the transition from the vapor to the plasma regimes. We briefly discuss a method for combining two new vapor regime treatments with plasma regime theory, giving a smooth transition from one regime to the other. We conclude with a section on future directions.

Recent work has brought about a renewed interest in CO2 laser ablation studies of polyoxymethylene, due to its potential as a test target for enhancing modern understanding of the laser ablation process. In this paper, new results taken in air at atmosphere pressure are reported, including data measured at institutions in Germany and Japan, which increase the body of literature data on CO2 laser ablation of polyoxymethylene. The results are discussed in terms of aerospace parameters such as the momentum coupling coefficient and specific impulse, and are compared to a previous literature study. The threshold fluence is specified for ablation of polyoxymethylene by CO2 laser radiation. Fluences higher (and lower) than previously tested for CO2 laser ablation were studied herein, and record specific impulse values for CO2 laser ablation of flat polyoxymethylene are also reported here.

A CO2 laser was operated at pulse energies up to 10 J to ablate polyoxymethylene targets in air and vacuum conditions. Critical effects predicted by ablation models are discussed in relation to the experimental data, including specifically the threshold fluences for vaporization and critical plasma formation, and the fluence at which the optimal momentum coupling coefficient is found. Finally, we discuss a new approach for modeling polymers at long wavelengths, including a connection formula that links the vaporization and plasma regimes for laser ablation propulsion.

It is a relevant issue in the research on laser propulsion that experimental results are treated seriously and that meaningful scientific comparison is possible between groups using different equipment and measurement techniques. However, critical aspects of experimental measurements are sparsely addressed in the literature. In addition, few studies so far have the benefit of independent confirmation by other laser propulsion groups. In this paper, we recommend several approaches towards standardization of published laser propulsion experiments. Such standards are particularly important for the measurement of laser ablation pulse energy, laser spot area, imparted impulse or thrust, and mass removal during ablation. Related examples are presented from experiences of an actual scientific cooperation between NU and DLR. On the basis of a given standardization, researchers may better understand and contribute their findings more clearly in the future, and compare those findings confidently with those already published in the laser propulsion literature. Relevant ISO standards are analyzed, and revised formats are recommended for application to laser propulsion studies.

The topic of area scaling is of great importance in the laser propulsion field, including applications to removal of space debris and to selection of size ranges for laser propulsion craft in air or vacuum conditions. To address this issue experimentally, a CO2 laser operating at up to 10 J was used to irradiate targets. Experiments were conducted in air and vacuum conditions over a range of areas from about 0.05–5 cm2 to ablate flat polyoxymethylene targets at several fluences. Theoretical effects affecting area scaling, such as rarefaction waves, thermal diffusion, and diffraction, are discussed in terms of the experimental results. Surface profilometry was used to characterize the ablation samples. A CFD model is used to facilitate analysis, and key results are compared between experimental and model considerations. The dependence of key laser propulsion parameters, including the momentum coupling coefficient and specific impulse, are calculated based on experimental data, and results are compared to e...

When a weak shock wave reflects from wedges its reflection pattern does not appear to be a simple Mach reflection. This reflection pattern is known to be von Neumann Mach reflection in which a Mach stem can not necessarily be straight. In this paper the local change of the Mach stem curvature was experimentally and numerically investigated. A distinct triple point, at which the curvature becomes infinite as appears in a simple Mach reflection, was not observed but the Mach stem curvature became a maximum between foot of the Mach stem and a point, P1, at which an incident shock met with a reflected shock. Maximum curvature point P2 and P1 do not coincide for small wedge angles and tend to merge over a certain wedge angle. Experimental results agreed with numerical results. The trajectory angle of P2 was found to be expressed well by Whitham's shock-shock angle.

Experimental and analytical studies have been conducted on the performance and thrust production mechanisms of an applied-field magnetoplasmadynamic thruster. The thruster was able to run with a high-thruster performance due to large electromagnetic effects related to the applied magnetic field. Using hydrogen, helium, and argon as the propellant, over 20 percent thrust efficiency was obtained over a wide specific impulse range from 1000 to 7000 s at input power levels between 2.2 and 15.9 kW. From the measurements of performance characteristics and current densities in the acceleration region, and by a theoretical analysis, it is found that the thruster operation is characterized by a parameter, B-squared/m (B: applied magnetic field strength, m: propellant mass flow rate). 9 refs.

Experiments were conducted using a 25-mm-bore ram accelerator. By varying the projectile mass and the mixture fill pressure, the projectile acceleration level was varied by a factor of three. The acceleration performance is evaluated based on a ballistic efficiency. Over a velocity range from 80% to 110% of Chapman-Jouguet detonation velocity, the ballistic efficiency was kept almost constant, and did not depend on the acceleration level.

*† ‡ § Numerical simulations of the impulse generation during the irradiation of a TEA CO2 laser pulse onto a polyacetal target are presented. The calculations account for the thermal conduction within the polyacetal target, the vaporization process under equilibrium assumption through the Clausius-Clapeyron equation, and the expansion of the vapor in a 2D-axysimmetric flowfield geometry under thermochemical equilibrium assumption. It is found that the present method can reproduce the time-resolved impulse data measured for various sets of laser energies and spot diameters in a near vacuum condition.

Measurements of the drag over a flat-nosed cylinder with repetitive laser pulse irradiations ahead of it were conducted in a Mach-2, in-draft wind tunnel. Laser pulses were focused using a plane-convex lens fabricated on the nose of the cylinder at a repetition frequency of up to 10 kHz and an effective power of 70 W at a maximum. The drag was measured using a low-friction piston which was backed by a load cell in a cavity at a controlled pressure. The measurement was so delicate that careful implementation was necessary to accurately determine the amount of drag reduction. A drag reduction about 1.4 N which corresponds to an efficiency of energy deposition over 1400 % was obtained. Nomenclature A = projection area of cylinder body D = cylinder diameter F = force f = laser pulse repetition frequency L = distance between cylinder head and laser focus P = pressure P0 = atmospheric pressure Psub = pressure in sub-chamber t = time W = time-averaged laser power α = fitting constant

For the future space propulsion system, the laser propulsion is expected to be a useful method. The most prominent advantage of the laser propulsion is that the system can generate the impulse without carrying the power supply onboard. This propulsion system has the possibility to improve the payload ratio compared to the conventional chemical propulsion system. Therefore, many researches have been conducted, since Kantrowitz’s proposal of the laser propulsion. Recent studies have shown that an ablative laser propulsion, in which laser ablation of solid propellant is used in a propulsive system, is an optimum method to obtain the impulse more efficiency in space. From 1960s’, the impulse characteristics generated by the single laser have been investigated by many researchers, for the variety of combinations of the laser types and target materials. Recently, the repetitively irradiated laser pulses effect on polymers have been investigated. In 2004, Phispps reported the novel type laser ablation thruster. His thruster could generate thrust by irradiating the laser pulses onto the virgin spots which were slid successively as like tape reel. However, until recently, the impulse characteristics of the repetitively irradiating laser onto the fixed spot have not been investigated. Recntly, Suzuki et.al., investigated the time-integrated impulse characteristics by using the ballistic pendulum system. He investigated the impulse characteristics for the combination of CO2 laser and POM target by the repetitive laser pulse irradiation onto the fixed spot. Figure 1 shows his representative result. For the initial phase(1 ≤ N ≤ 10), the morphology and contamination of the virgin target surface degraded the impulse performance. After initial phase(10 ≤ N ≤ 100), gradual increase of the momentum coupling coefficient with increasing the laser pulse repetition number was observed. Here, N represents the total number of laser pulses. He suggested that this impulse increase was related to the formation of the crater. In a word, the impulse performance can be changed with the variation of the morphology of the surface target. From Suzuki’s result, it is expected that the impulse characteristics of other combinations of laser wave length and the target materials also depends on the total number of laser pulses. However, in Ref., only one combination between the laser and the target material, that is, CO2 laser and POM target was investigated. Therefore, the investigation of the impulse characteristics by the repetitive laser irradiation for other materials is inevitable. Especially, the repetitive laser pulse effect on the aluminum impulse characteristics is expected to offer useful information for not only the laser propulsion performance improvement but also the debris de-orbiting application. The purpose of this study is to investigate the time averaged impulse characteristics of aluminum by the repetitive laser irradiation on the fixed point. This paper introduces the primitive result, as a first step. ∗Assistant Professor, e-mail; matsuda@nuae.nagoya-u.ac.jp, Department of Aerospace Engineering, AIAA Member †Associate Professor, Department of Aerospace Engineering, AIAA Member. ‡Professor, Department of Aerospace Engineering, Associate Fellow.

Experimental study is performed to investigate the effect of turbulence on weak shock wave propagation. The creation of shock wave is done by focusing an Nd:YAG laser pulse, and the turbulence is produced as a slit jet. An overpressure history past the slit jet is measured using a piezoelectric pressure transducer. The measured pressure modulation characteristics are related to flow visualization using a Schlieren system. Due to the slit jet, their standard deviations are vastly increased while the peak overpressure on average is slightly decreased. The modulation of the overpressure through the turbulence depends on the shape of the shock wave.

Two novel ‘double-beam’ techniques to enhance laser-ablative impulse are tested: Twowavelength technique and preheating technique. The two-wavelength technique is demonstrated using a Nd:YAG laser, and is found effective for the laser fluence less than 10 J/cm 2 both for metal and plastic ablators. The preheating technique is demonstrated using a TEA CO2 pulse laser. The laser pulse is irradiated onto a preheated plastic ablator. It is found that at 200 deg. C, the laser-ablative impulse is two-times as large as at a normal temperature.

Numerical analyses have been conducted on radiative heat transfer from hypersonic, non-equilibrium air shock layers over a reentry body. The band method developed here enables one to conduct wavelength-dependent, three-dimensional radiative transfer calculation in which self-absorption effect is taken into account. The radiative heat transfer calculated here was found comparable with convective one. Atomic species and N2+ were found to be dominant radiators. Electrons play an essential role in determining radiative emission power. Due to a high electron temperature, a peak in emission power exists immediately behind the shock. At a high Mach number, since electron density is at a high level, another peak appears near the wall, thereby enhancing the radiative heat transfer at the stagnation point and enlarging the half-width of the radiative heat flux to the wall.

Proof-of-principle experiments of in-tube propulsion in which the propellant was supplied from the launch tube wall were conducted. The launch tube had a 25 mm × 25 mm square inner cross-section. A pair of opposing launch tube walls were made of polyacetal (POM), which was ablated using repetitive Transeversely-Excited Atmospheric (TEA) CO2 laser pulses. The laser beam was sent through a ZnSe window at the tube bottom to the symmetric parabolic surfaces of the projectile, and focused onto the ablator surfaces. The momentum coupling coefficient was measured from a vertical launch trajectory. When the breech of the launch tube was plugged, a momentum coupling coefficient of 4 mN-s/J at least was obtained. Even when the breech was connected to a vacuum chamber at a pressure lower than 20 Pa, the projectile could be vertically launched with a constant momentum coupling coefficient of 0.14 mN-s/J, the value of which was the same order as that obtained by directly irradiating a laser pulse onto a POM ablator.

The effect of the repetition frequency on the behavior of the laser induced plasma was qualitatively investigated in the quiescent atmospheric air. The plasma behavior induced by the second or later laser pulse depends on the repetition frequency. In the case of the repetition frequency of 200 Hz, the plasma behavior was almost independent of each laser pulse. On the other hand, in the case of the repetition frequency more than 1 kHz, the behavior of the plasma induced by the second or later laser pulse is prominently different from that induced by the first laser pulse. That is, while the front lobe is generated in the plasma decay process for the first laser pulse induced plasma, the front lobe can not be observed for the second or later laser pulse. Based on the experimental results in this study, whether the front lobe is generated in the plasma induced by the second or later laser pulse indicates the interaction of the plasma induced by each repetition laser pulse.

The laser-driven in-tube accelerator in which the propellant is supplied from laser-ablated gas from the tube wall was developed. Proof-of concept demonstrations of vertical launch were successfully done. The device had a 25mm X 25mm square cross-section; two opposing walls were made of polyacetal and acted as the propellant, the other two acrylic window with guide grooves to the projectile. The upper end of the launch tube was connected to a vacuum chamber of an inner volume of 0.8 m 2 , in which the initial pressure was set to lower than 20 Pa. With plugging the bottom end of the launch tube, a momentum coupling coefficient exceeding 2.5 mN/W was obtained. Even with the bottom end connected to the same vacuum chamber through a different duct, the projectile was vertical launched successfully, obtaining 0.14 mN/W.

Pressure time variations and associated flows induced by pulsed laser ablation were experimentally studied using the Velocity Interferometer System for Any Reflector (VISAR) and framing Schlieren visualization. The combination of either aluminum or polyacetal target and TEA CO2 laser pulse were examined. The VISAR measurement resolved that the pressure modulated from the laser power variation in the impulse generation processes. Integrated impulse induced by repetative CO2 laser pulses was measured using a torsion‐type impulse balance. The effect of the ambient pressure was significant. The measured impulse characteristics were closely associated with target surface morphology and fluid dynamics.

Laser‐driven, in‐tube accelerator is a laser propulsion device in which the impulse performance is enhanced by the confinement of the compressible fluid. This paper describes the conceptual origin and state of the art of this technology.

Modulation of shock foot oscillation due to energy deposition by repetitive laser pulses in shock wave-boundary layer interaction over an axisymmetric nose-cylinder-flare model in Mach 1.92 flow was experimentally studied. From a series of 256 schlieren images, density oscillation spectra at each pixel were obtained. When laser pulses of approximately 7 mJ were deposited with a repetition frequency, fe, of 30 kHz or lower, the flare shock oscillation had a peak spectrum equivalent to the value of fe. However, with fe of 40 kHz–60 kHz, it experienced frequency modulation down to lower than 20 kHz.

The effect of ambient pressure on the interaction between a laser plasma bubble and a shock wave involving a Richtmyer-Meshkov instability was experimentally studied via framing Schlieren visualization. A sharp plasma interface could be formed without any separation material that causes undesired disturbances. The fundamental vortex structure which was produced via baroclinic effects was self-similar with respect to the laser energy-ambient pressure ratio. Yet, the higher the ambient pressure, the more high-wave-number instabilities were enhanced so as to contaminate the self-similarity.

The aim of the present study is to clarify the time-dependent characteristics of the impulsive force generated by irradiating a laser pulse onto metallic and polymer materials. A Velocity Interferometer System for Any Reflector (VISAR) is employed to measure the acceleration driven by the laser ablation. The VISAR has two delay-lines that enable the velocity measurement in the range from 10 m/s to 100 m/s. The ablation impulse is inferred from the measured acceleration history. Th e influence of the ambient air on the ablation pressure is investigated for aluminum using a Nd:YAG laser (wavelength: 1064 nm, pulse energy < 1 J, pulse duration ~ 10 ns) and for a polymer material using a CO 2 laser (wavelength: 1.06 P m, pulse energy < 10 J, pulse duration ~ 2 P s). The results of the preliminary experiments revealed the promising potential of the VISAR measurement. Keywords: Force measurement, velocity interferometer, Nd:YAG, CO 2 laser 1. INTRODUCTION The impulse-generation by laser-ablation is expected to provide novel techniques for such aerospace applications as space-debris removal, orbit transfer, and launch from the ground. From 1960’s, a number of studies have been conducted for the impulse generation processes by irradiating a laser pulse. [1-5] Phipps et al [5] proposed a scaling law for the laser-ablative impulse of metals and polymers in v acuum. Watanabe and Sasoh [6] tested several techniques to enhance the impulse generated on polymer materials. Time-resolved measurements are useful to understand the unsteady processes in more detail expanding the application capability of laser ablation. The present study investigates the acceleration history generated on an al uminum surface irradiated by a Nd:YAG la ser pulse in the presence of the air. Previous researches have clarified the time-integrat ed characteristics of the impulse for many cases. 2. EXPERIMENT METHODS 2.1. Principles and preliminar y tests of VISAR measurement Velocity Interferometer System for Any Reflector (VISAR) is the interferometer system to measure the velocity with nano-seconds time resolution. VISAR was invented by Barker[7-9], and has been employed in the impact studies.[7-11] Recently, it is also applied in the studies of the laser- material-processing. [12-14] Figure 1 shows the schematic diagram of the velocity interferometer. Linearly polarized probe-beam is reflected from the back-surface of a target. When the target moves with the velocity at U , the frequency of reflected light is Doppler-shfted by ' &

Expansion tube has a theoretical potential to realize a ultra-high-enthalpy flow for simulating acrothermodynamics of super-orbital entry flights capsule. However, since test gas stagnates at the secondary diaphragm for rupturing diaphragm, an ideal test gas is not obtained. The influence of the secondary diaphragm conditions on the test gas flow in expansion tube was examined through the shadowgraph image of framing interval ljs and the pressure measurement. By using adequately-thin diaphragm, e.g. Mylar sheet of 3im-thickness, as the secondary diaphragm, the rupture process got close to the ideal and the reflection shock wave could be reduced. Test gas flow of shock speed of about 7.5 km/s was maintained for 30Os for the pressure of gas in the shock tube = 3.5kPa and that of acceleration tube = 16Pa.

DOI: 10.2514/1.23846 An experimental study of expansion tube operation was conducted by highlighting the interference due to the secondary diaphragm, which separates the shock and acceleration tubes, upon the shock wave transition past the separation. The in-tube processes were diagnosed by framing shadowgraphs and on-wall pressure measurements. Among commercially available diaphragm materials examined, only when using the thinnest Mylar diaphragm (3 � m in thickness), was the shock wave transition not accompanied by serious flow disturbance due to shock wave reflection or to pressure loss through the cloud of ruptured diaphragm fragments. Although cellophane diaphragm was more brittle and suitable for fragmentation, it had the mass penalty caused by its smaller tensile stress and commercial availability, thereby resulting in much larger disturbances.

Understanding the dynamics of laser-produced plasma is essentially important for in- creasing available thrust force in a gas-driven laser propulsion system such as laser-driven in-tube accelerator. A computer code is developed to explore the formation of expand- ing nonequilibrium plasma produced by laser irradiation. Various properties of the blast wave driven by the nonequilibrium plasma are examined. It is found that the blast wave propagation is substantially affected by radiative cooling effect for lower density case. Recently, laser propulsion systems that acquire thrust force by laser en- ergy are extensively examined by using various facilities. A typical example of such gas-driven laser propulsion system is the Laser-driven In-Tube Accelerator: LITA, 1 which is developed at the Institute of Fluid Science, Tohoku University. In this propulsion system, relatively high thrust can be obtained by placing a projectile in an acceleration tube which is filled by inert propellant gas. 2,3 A schematic illustration of LITA operation is shown in Fig. 1. The projectile placed in the acceleration tube consists of a centerbody, a shroud and struts. Since the base of the centerbody is shaped as parabola, the incident pulse laser beam from the rear side of the projectile is reflected at the base and focused behind the centerbody. Then a breakdown occurs at the focal point and free electrons appear. These free electrons absorb the laser beam energy by inverse bremsstrahlung. As a result, high temperature and high pressure plasma core region is formed, which then induces a blast wave. This blast wave impinges on the projectile base and a thrust force is given to the projectile. Therefore the performance of the gas-driven laser propulsion system highly depends on the blast wave dynamics as well as on the plasma state that sustains the blast wave. In our previous work, a two-dimensional computational method was devel- oped to clarify the physical phenomena in the LITA acceleration tube, where a blast wave was sustained by the laser-produced nonequilibrium plasma. 4 Al- though various features of the blast wave were successfully reproduced, the computed pressure value at the acceleration tube wall was found to be sub- stantially higher than that measured in the experiment. A possible cause of this discrepancy is suggested in Fig. 2, where the emission spectra from the focal point obtained in the experiment are compared with that

Flow visualizations of the interaction between a laser‐pulse‐generated plasma and a shock wave driven by it have been experimentally conducted. The configuration of the experimental set‐up corresponds to the laser‐driven, in‐tube accelerator. Primary‐mode deformation of the plasma is governed by Richtmyer‐Meshkov instability which is produced by the vector product between the pressure and density gradients, which in turn correspond to a reflected shock wave and to the plasma, respectively. Higher‐mode contact surface deformations are supposedly originated in Rayleigh‐Taylor instability in the shrinkage phase of the plasma, and is enhanced due to the passage of the reflected shock wave.

To achieve a higher thrust performance in the laser‐driven in‐tube accelerator operation, numerical analysises have been carried out. The computational code covers from the generation of the blast wave to its interactions with the projectile and the acceleration wall. The thrust history and the momentum coupling coefficient evaluated from the numerical simulation depend on the fill pressure and the projectile shape. The confinement effect can be clearly found using the projectile attached with a shroud.

Understanding the dynamics of laser‐produced plasma is essentially important for increasing available thrust force in a gas‐driven laser propulsion system such as laser‐driven in‐tube accelerator. A computer code is developed to explore the formation of expanding nonequilibrium plasma produced by laser irradiation. Various properties of the blast wave driven by the nonequilibrium plasma are examined. It is found that the blast wave propagation is substantially affected by radiative cooling effect for lower density case.

Single pulse laboratory experiments were carried out with a high‐power CO2 Transversely‐Excited Atmospheric (TEA) laser using three laser pulsejet engines, shaped as parabolic bells, measuring 11‐cm in diameter. Assuming the vertex is set at the parabola’s focus, the “calibration bell” engines had three different total divergence angles of 60, 87.2, and 120 degrees (i.e., viewing outward towards the 11‐cm nozzle exit plane). The objective was to quantify and calibrate the effects of laser pulse duration upon the momentum coupling coefficient (Cm) performance from the two CO2 lasers, using laser pulse energy as the parametric variable. Bell engine performance data from the TEA laser are contrasted with former results from the PLVTS CO2 electron discharge laser (EDL). The single‐pulse PLVTS tests were conducted in Sept. 2000 and Sept. 2001, revealing that the impulse and Cm performance of the 60° bell generally exceeded the 87.2° engine, which in turn outperformed the 120° bell. With PLVTS, the maximum single‐pulse Cm varied from 275 to 375 N‐sec/MJ. In contrast, the 2 microsecond TEA laser tests generated results that were distinctively different from that of the EDL. Both tests used a standard ballistic pendulum to measure airbreathing engine performance at a pressure of one atmosphere.

The velocity interferometer experiments provided the time‐resolved measurements of impulsive force generated on ablators of different materials by laser ablation. In the preliminary experiments, a Nd:YAG pulse laser beam was irradiated on an aluminum‐foil. The laser pulse energy was 0.5 J at the maximum, and its full width at the half maximum (FWHM) was 7 ns. The history of impulsive force was inferred from the velocity history of the foil surface, which was measured using the velocity interferometer with the time resolution at 6.5‐ns. The results showed that the impulsive force continued for more than 40‐ns when the pulse duration is less than 20‐ns.

In this study, impulse generation processes induced by a single laser pulse in the laser‐driven in‐tube accelerator are studied through pressure history measured at the center of the projectile base, which acts also as a parabolic mirror. The effects of the fill pressure, laser energy and length of a shroud are analyzed.

*† ‡ § Numerical simulation of unsteady flowfield in an expansion tube is carried out using a contact surface resolving technique for sharply capturing the contact surface between the driver gas and the test gas. The Navier-Stokes equations in the axisymmetric form with thermochemical nonequilibrium are solved. The numerical flux function at the boundary of coexisting region is modified by extrapolation with enforcing monotonicity. Calculated results show that the contact surface is sharply captured and the contamination of the test gas region due to driver gas is well suppressed. By capturing the contact surface sharply, the disturbance along the contact surface in the radial direction becomes evident in the computed results. An emergence of hydrodynamical instability is suggested. It is also found that the onset of the test time varies substantially because the high-temperature acceleration gas region is well captured when the contact surface is resolved sharply. This clearly suggests the importance of the present contact surface resolving technique.

The paper focuses on physical gas-dynamic characteristics of impulse generation by laser Induced blast wave (LIBW) in a laser-driven in tube accelerator (LITA). Propagation, reflection of blast wave and wave structure were intensively studied by using an ICCD camera system through shadowgraph.

In this paper, we will report recent results of LITA 25 experiments, which include framing schlieren visualization and streak spectroscopy. The processes of laser energy absorption, laser plasma and blast wave generation, and their interactions are clearly observed.