Quasi-isentropic Compression Research Articles

Verification of conventional equations of state for tantalum under quasi-isentropic compression

Shock Hugoniot data have been widely used to calibrate analytic equations of state (EOSs) of condensed matter at high pressures. However, the suitability of particular analytic EOSs under off-Hugoniot states has not been sufficiently verified using experimental data. We have conducted quasi-isentropic compression experiments (ICEs) of tantalum using the compact pulsed power generator CQ-4, and explored the relation of longitudinal stress versus volume of tantalum under quasi-isentropic compression using backward integration and characteristic inverse methods. By subtracting the deviatoric stress and additional pressure caused by irreversible plastic dissipation, the isentropic pressure can be extracted from the longitudinal stress. Several theoretical isentropes are deduced from analytic EOSs and compared with ICE results to validate the suitability of these analytic EOSs in isentropic compression states. The comparisons show that the Gruneisen EOS with Gruneisen Gamma proportional to volume is accurate, regardless whether the Hugoniot or isentrope is used as the reference line. The Vinet EOS yields better accuracy in isentropic compression states. Theoretical isentropes derived from Tillotson, PUFF, and Birch-Murnaghan EOSs well agree with the experimental isentrope in the range of 0–100 GPa, but deviate gradually with pressure increasing further.

Fabrication of graded density impactor via underwater shock wave and quasi-isentropic compression testing at two-stage gas gun facility

We show direct evidence that underwater shock wave enables us to bond multithin plates with flat, parallel, and high-strength interfaces, which are key requirements for functionally graded material (also called graded density impactor). This phenomenon is ascribed to the super short duration of the high-speed underwater shock wave, reducing the surface tension, diffusion, evaporation, deposition, and viscous flow of matter. Thin magnesium, aluminum, titanium, copper, and molybdenum foils were welded together and designed with the increase in density. Experimental evidence and numerical simulation show that well bonding between the multilayer structures. Microstructure examinations reveal that the dominant interfacial form shifts from waviness to linearity. Graded density impactor with multilayer structure is proved that can produce quasi-isentropic compression in two-stage gas gun experiment with a designed pressure loading profile, which suggests a feasible method to simulate the conditions we want to study that were previously inaccessible in a precisely controlled laboratory environment.

Sub-100 ps laser-driven dynamic compression of solid deuterium with a ∼40 μJ laser pulse

We dynamically compress solid deuterium over <100 ps from initial pressures of 22 GPa to 55 GPa, to final pressures as high as 71 GPa, with <40 μJ of pulse energy. At 25 GPa initial pressure, we measure compression wave speeds consistent with quasi-isentropic compression and a 24% increase in density. The laser drive energy per unit density change is 109 times smaller than it is for recent longer (∼30 ns) time scale compression experiments. This suggests that, for a given final density, dynamic compression of hydrogen might be achieved using orders of magnitude lower laser energy than currently used.

Generation of isentropic compression by use of multi-layer composite flyer and its influence on system thermodynamics: A simulation study

Recently the possibility of achieving quasi-isentropic compression using functionally graded materials, in both gas gun and explosive driven systems was explored by hydro-dynamic simulations. In the current paper, we show that multi-layered composite flyer with progressively increasing shock impedances, referred to as graded density impactor (GDI), has the potential to enable increased flexibility in suitably tailoring the applied-pressure profiles, further relaxing constraints on the thermodynamic path of compressed material. Present simulation study pertaining to constant velocity impact of GDI reveals that linear ramp pulses of different pressure rise times, with comparable peak values can be realized only by changing the layer thicknesses of a particular GDI. We report generation of three different slope ramp pulses by five layer GDI made of PMMA, Al, Ti, Cu and Ta with different set of thicknesses obtained by genetic algorithm based optimization technique. Generation of long duration (μs) isentropic pressures using discrete GDI is a significant step, since it is devoid of fabrication difficulties of ultra-thin lamellae of FGM. Signatures of isentropic compression of a thin Cu target under different slope ramp loadings are identified from basic thermodynamic aspects in terms of temperature rise and entropy production. It is shown that that extent of entropy increase is closely related to the slope of ramping pulse. Further, a physical model has been constructed to determine approximate time profile of pressure pulse generated by equal layer-width GDI.

Progress in warm dense matter study with applications to planetology

We present an overview of some recent theoretical and experimental results obtained on the properties of iron and silica at conditions encountered in planetary interiors. The first part is concerned with the development of x-ray absorption near edge spectroscopy in dynamical experiments using high-energy lasers as a tool to investigate phase transitions and structural changes at extreme pressure–temperature conditions for these two key constituents. The second part focuses on the development of a quasi-isentropic compression technique to achieve the pressure–temperature conditions anticipated in planetary interiors (3–10 Mbar, 5000–8000 K). The experiments were performed using the LULI, LLNL and LIL high-energy lasers’ facilities. The experimental results are analyzed using first-principle simulations based on density functional theory.

Experimental progress of quasi-isentropic compression under drive condition of Shen Guang-Ⅲ prototype laser facility

Laser indirect-drive has the potential to obtain ultra-high pressure which is very useful for shock physics. The isentropic compression can be obtained with reservoir target in laser indirect-drive experiment. The free surface velocity and interface velocity are the two important parameters in isentropic compression experiment. The efficiency with reservoir target is lower than that in the isentropic compression experiment with long pulse laser direct-drive. However, the isentropic compression experiment with long pulse in laser direct-drive is very sensitive to the laser intensity variation. In this paper, the isentropic compressions with reservoir target with indirect-drive and direct-drive on Shen Guang-Ⅲ prototype laser facility are investigated separately. And the important technique is introduced to provide the reference data in this field. And the isentropic compression with long pulse laser direct-drive is analyzed on Shen Guang-Ⅲ prototype laser facility. The interface velocity on Al/LiF is achieved with three steps. The blank effect is provided and analyzed. These data show that with long pulse in laser direct-drive, a pressure, which has been highest in China up to now, can be obtained. With these experiment data, the feasibility to do the isentropic compression experiment on Shen Guang-Ⅲ prototype laser facility has been approved.

磁驱动准等熵压缩下单晶氟化锂的光学特性

磁驱动准等熵压缩下单晶氟化锂的光学特性

Recent advances in hyper-velocity flyer launch experiments on PTS

Magnetically driven loading technology is to load the large pulse current to the test area through the pulsed power, which forms a smooth magnetic pressure rising over time to achieve a quasi-isentropic compression of sample and hyper-velocity flyer launch. Based on the output characteristics and parameters of PTS accelerator, two types of hyper-velocity flyer launch experiments with different load configurations, such as the load, flyer plates size, current waveform and diagnostic systems etc, are designed and tested. LY12 aluminum flyer plates with dimensions of 10 mm0.725 mm was launched by single-sided stripline load configuration to 11.5 km/s while the magnetic drive load pressure is near 0.9 10^5 MPa. Simulation and experimental results agrees well with those of in the flyer launch process and the ultimate velocity. Further simulation shows that the launch velocity of aluminum flyer plates with dimensions of 8.5 mm1 mm is expected to exceed 15 km/s under the program of optimizing the structural parameters and regulation. The design and experiment technology of hyper-velocity flyer launch based on multi-branch pulsed power generator has been mastered during the designs and experiments.

Phase transition of iron under magnetically driven quasi-isentropic compression

The technique of magnetically driven quasi-isentropic compression is a new experimental technology which can generate dynamic ramp compression, and its load path lies between the quasi-static (isothermal) and shock compression (adiabatic process), it is a bridge to contact the two traditional loading techniques. In this paper, the phase transition experiments of iron were done under magnetically driven quasi-isentropic compression technology on the facility CQ-4, and the effect of acoustic impedance on the interface velocity was analyzed. Simulation with multi-phase equation of state also was done to analyze the phase transition, and the simulations show that the phase transition relaxation time is about 30ns, and that the phase transition pressure is about 13 GPa, and that the numerical and experimental interface velocities are essentially coincident. With the analysis of evolution of the stress wave in the sample, it shows that the sound speed drop and the acoustic impedance of the window are the main factors to affect the interface velocity waveform.

Metal liner-driven quasi-isentropic compression of deuterium

Properties of degenerate hydrogen and deuterium (D) at pressures of the order of terapascals are of key interest to Planetary Science and Inertial Confinement Fusion. In order to recreate these conditions in the laboratory, we present a scheme, where a metal liner drives a cylindrically convergent quasi-isentropic compression in a D fill. We first determined an external pressure history for driving a self-similar implosion of a D shell from a fictitious flow simulation [D. S. Clark and M. Tabak, Nucl. Fusion 47, 1147 (2007)]. Then, it is shown that this D implosion can be recreated inside a beryllium liner by shaping the current pulse. For a peak current of 10.8 MA cold and nearly isochoric D is assembled at around 12 500 kg/m3. Finally, our two-dimensional Gorgon simulations show the robustness of the implosion method to the magneto-Rayleigh-Taylor instability when using a sufficiently thick liner.

Isentropic compression of hydrogen: Probing conditions deep in planetary interiors

We perform ab initio calculations for the equation of state of dense liquid hydrogen and deuterium using quantum molecular dynamics simulations based on finite-temperature density functional theory. This extensive data set allows us to determine specific density-temperature-pressure tracks such as the cold curve, precompressed and principal Hugoniot curves, and isentropes which are essential for the analysis and interpretation of high-pressure experiments. In this study we focus on conditions probed by recent quasi-isentropic shock compression experiments that have reached a so-far unprecedented 108-fold compression of gaseous deuterium. As these states of matter are relevant for the deep interior of Jupiter-like exoplanets we simultaneously give predictions for their isentropes.

The hydrodynamics of astrophysical jets: scaled experiments and numerical simulations

Context. In this paper we study the propagation of hypersonic hydrodynamic jets (Mach number > 5) in a laboratory vessel and make comparisons with numerical simulations of axially symmetric flows in the same initial and boundary conditions. The astrophysical context is that of the jets originated about Young Stellar Objects (YSOs). Aims. In order to gain a deeper insight into the YSO jets phenomenology, we have performed a set of experiments and numerical simulations of hypersonic jets in the range of Mach numbers from 10 to 20 and for jet-to-ambient density ratios from 0.85 to 5.4, using different gas species and observing jet lengths of the order of 150 initial radii or more. Exploiting the scalability of the hydrodynamic equations, we intend to reproduce the YSO jet behaviors as far as the jet velocity and elapsed times are concerned. In addition, we can make comparisons between the simulated, the experimental and the observed morphologies. Methods. In the experiments the gas pressure and temperature are increased by a fast, quasi isentropic compression by means of a piston system operating on a time scale of tens of millisecond, while the gas density is visualized and measured by means of an electron beam system. We have used the PLUTO software for the numerical solution of mixed hyperbolic/parabolic conservation laws targeting high Mach number flows in astrophysical fluid dynamics. We consider axisymmetric initial conditions and carry out numerical simulations in cylindrical geometry. The code has a modular flexible structure whereby different numerical algorithms can be separately combined to solve systems of conservation laws using the finite volume or finite difference approach based on Godunov-type schemes. Results. The agreement between experiments and numerical simulations is fairly good in the majority of comparisons. The resulting scaled flow velocities and elapsed times are close to the ones shown by observations. The morphologies of the density distributions agree with the observed ones as well. Conclusions. The laboratory and the simulated hypersonic jets are all pressure matched, i.e. their axial regions are almost isentropic at the nozzle exit. They maintain their collimation for long distances in terms of the initial jet radii, without including magnetic confinement effects. This yields a qualitatively good agreement with the observed YSO jets morphologies. It remains to be seen what happens when non axially symmetric perturbations of the flow are imposed at the nozzle both in the experiment and in the simulation.

Direct laser-driven ramp compression studies of iron: A first step toward the reproduction of planetary core conditions

The study of iron under quasi-isentropic compression using high energy lasers, might allow to understand its thermodynamical properties, in particular its melting line in conditions of pressure and temperature relevant to Earth-like planetary cores (330–1500 GPa, 5000–8000 K). However, the iron alpha-epsilon solid–solid phase transition at 13 GPa favors shock formation during the quasi-isentropic compression process which can depart from the appropriate thermodynamical path. Understanding this shock formation mechanism is a key issue for being able to reproduce Earth-like planetary core conditions in the laboratory by ramp compression. In this article, we will present recent results of direct laser-driven quasi-isentropic compression experiments on iron samples obtained on the LULI 2000 and LIL laser facilities.

整形激光加载的一维准等熵压缩仿真

整形激光加载的一维准等熵压缩仿真

A 4 MA, 500 ns pulsed power generator CQ-4 for characterization of material behaviors under ramp wave loading

A pulsed power generator CQ-4 was developed to characterize dynamic behaviors of materials under ramp wave loading, and to launch high velocity flyer plates for shock compression and hypervelocity impact experiments of materials and structures at Institute of Fluid Physics, China Academy of Engineering Physics. CQ-4 is composed of twenty capacitor and primary discharge switch modules with total capacitance of 32 μF and rated charging voltage of 100 kV, and the storage energy is transmitted by two top and bottom parallel aluminum plates insulated by twelve layers of polyester film with total thickness of 1.2 mm. Between capacitor bank and chamber, there are 72 peaking capacitors with total capacitance of 7.2 μF and rated voltage of 120 kV in parallel, which are connected with the capacitor bank in parallel. Before the load, there is a group of seven secondary self-breaking down switches connected with the total circuit in series. The peaking capacitors and secondary switches are used to shape the discharging current waveforms. For short-circuit, the peak current of discharging can be up to 3 ~ 4 MA and rise time varies from 470 ns to 600 ns when the charging voltages of the generator are from 75 kV to 85 kV. With CQ-4 generator, some quasi-isentropic compression experiments under ramp wave loadings are done to demonstrate the ability of CQ-4 generator. And some experiments of launching high velocity flyer plates are also done on CQ-4. The experimental results show that ramp wave loading pressure of several tens of GPa on copper and aluminum samples can be realized and the velocity of aluminum flyer plate with size of 10 mm × 6 mm × 0.35 mm can be accelerated to about 11 km/s and the velocity of aluminum flyer plate with size of 10 mm × 6 mm × 0.6 mm can be up to about 9 km/s, which show that CQ-4 is a good and versatile tool to realize ramp wave loading and shock compression for shock physics.

Quasi-isentropic compression of dense gaseous helium at pressures up to 500 GPa

The thermodynamic parameters—pressure and density—of quasi-isentropically compressed helium have been measured in a pressure range of 100–500 GPa. A thermodynamic model that satisfactorily describes the behavior of strongly compressed helium in a wide range of compression parameters has been proposed.

Dynamic compression of solid HMX-based explosives under ramp wave loading

By means of the new techniques of magnetically driven quasi-isentropic compression based on compact capacitor bank facility CQ-1.5 developed by us, the dynamic compression of two mixed HMX-based plastic bonded explosives (PBX) explosives is researched under ramp wave loading. A pressure of 5–8 GPa over 600–800 ns is realized on explosive samples by optimizing loading electrodes and controlling charging voltages of CQ-1.5. And loading strain rates vary from 10 5 1/s to 10 6 1/s along the thickness of explosive samples. For experiments, the particle velocities of interface between explosive samples with different thicknesses and LiF windows are measured to determine material response by a displacement interferometry technique of Doppler pins system (DPS), and the experimental compression isentropes of researched explosives are obtained using the data processing method of backward integration and Lagrangian analysis for quasi-isentropic compression experiments, which are in agreement with the theoretical isentropes based on Mie-Gruneisen equation of state (EOS) and the results by Baer. For simulations, one-dimensional hydrodynamics code SSS is used to analyze the dynamic process, and the calculated results of particle velocity of interfaces are consistent with the experimental ones. Finally, one of the explosive constituents, the binder fluoride rubber F 2311 , is also investigated using this technique, and some properties under ramp wave loading are gained.

Virtual melting as a new mechanism of stress relaxation under high strain rate loading

Generation and motion of dislocations and twinning are the main mechanisms of plastic deformation. A new mechanism of plastic deformation and stress relaxation at high strain rates (10(9)-10(12) s(-1)) is proposed, under which virtual melting occurs at temperatures much below the melting temperature. Virtual melting is predicted using a developed, advanced thermodynamic approach and confirmed by large-scale molecular dynamics simulations of shockwave propagation and quasi-isentropic compression in both single and defective crystals. The work and energy of nonhydrostatic stresses at the shock front drastically increase the driving force for melting from the uniaxially compressed solid state, reducing the melting temperature by 80% or 4,000 K. After melting, the relaxation of nonhydrostatic stresses leads to an undercooled and unstable liquid, which recrystallizes in picosecond time scales to a hydrostatically loaded crystal. Characteristic parameters for virtual melting are determined from molecular dynamics simulations of Cu shocked/compressed along the 〈110〉 and 〈111〉 directions and Al shocked/compressed along the 〈110〉 direction.

Advances in quasi-isentropic compression experiments at institute of fluid physics of CAEP

The Advances in magnetically driven quasi-isentropic compression experiments (ICEs) at Institute of Fluid Physics of China Academy of Engineering Physics are introduced including the techniques, data processing methods and some typical application in dynamics of materials. Two apparatuses of CQ-1.5 and CQ-4 based on compact capacitor banks are described, which are used to do quasi-isentropic compression experiments and launch high velocity flyer plates. And some work of data processing methods of quasi-isentropic compression experiments is also presented in this topic. Finally, some applications of our generators in quasi-isentropic compression experiments of material dynamics are introduced, such as the experimental compression isentropes, phase transition, spallation of metals and elasto-plastic transition.

Laser-driven reservoir target for quasi-isentropic compression in aluminum

The quasi-isentropic compression of material with high strain rate can be obtained by the ramp wave loading of plasma jet produced by laser-driven reservoir target. The quasi-isentropic compression experiments of aluminum are carried out on the high power laser facility of SG-III prototype. The smooth and continuous speed history of free surface of specimen is recorded with a line-imaging velocity interferometer (VISAR). The peak pressure (60 GPa), the rise time of the load (～ 10 ns) and the strain (～ 108 s-1) are derived by the back-integrating method, and the reverberation of compression wave at the rear surface of the sample is observed.