Shock Wave Physics Research Articles

Numerical simulation of ultra-short laser pulse energy deposition and bulk transport for material processing

We have extended the physics of the one-dimensional radiation hydrodynamics simulation code HYADES to include processes important for studying laser–matter interaction with dielectrics and metals in the eV and sub-eV electron temperature range. Ultra-short laser pulses (USLP) are advantageous in many material processing situations where most of the absorbed laser energy appears in mass motion, and little appears as thermal energy. Major additions to the code include (1) the transport, reflection and absorption of laser light, (2) thermal energy transport and improved shockwave physics, and (3) improved models for the equation of state (EOS), strength of materials, and fracture. Examples from material processing and plasma generation were chosen for simulation. Our numerical simulations include the effects of radiation transport, hydrodynamic expansion and shockwave phenomena.

Shock-wave physics experiments with high-power proton beams

At the Karlsruhe Light Ion Facility (KALIF) high-power proton beams with power densities up to ∼ 1 TW/cm2 are generated depositing up to 40 kJ of ion energy in a focal spot of 6∼8-mm diameter. With peak proton energies of ∼ 1.7 MeV, specific power densities of up to 200 TW/g and energy densities of several MJ/g can be realized. This is a regime in which experiments providing information on the equation of state (EOS), dynamics of the beam interaction with condensed targets, and properties of solids and plasma at high-energy densities are of particular interest. In the present paper we report on shock-wave experiments using solid targets and high-resolution laser-Doppler velocimetry. The empirical data provided are used to verify code simulations and the used EOS-data in these calculations, to investigate the beam-target interaction, and to perform series of shock-wave measurements of properties of different materials. The ∼40-ns FWHM proton beam can be used to generate, by material ablation or impact of ablatively accelerated flyers, intense shock waves, permitting the investigation of shock compressibility, dynamic failure of solids under nanosecond load duration, phase transitions, and viscosity at strain rates up to ∼108 s-1. Recently an improved line-imaging velocimeter was set up to measure the spatial velocity variation with a maximum resolution of < 10 μm, opening the possibility to address new issues like growth of instabilities or local dynamics of the spall fracture.

Light-ion beam-target interaction experiments on KALIF

The performance of an extractor-type ion diode operated on the KALIF accelerator was improved recently to yield about 40 kJ of proton beam energy at an intensity of about 1 TW/cm2. With proton energies of 1.7 MeV simulations predict for the energy deposition layer in a solid target temperatures of several 10 eV, pressures in the 10 to 100 GPa range and densities which rapidly decay due to material ablation. One of the priority objectives of the target experiments program is to obtain empirical EOS data of the ablation plasma. So far, we investigated the hydrodynamic response of thin planar target foils using a laser Doppler velocimeter with high temporal resolution. Applying hydrodynamic relations used in shock-wave physics, one obtains the ablation pressure history. An analytical model based on an acoustic approximation was established allowing to explain details in the pressure response by characteristics of the ion beam profile. Spatially resolved investigation of the ablative acceleration history of thin target foils is under way.

A Near-infrared View of SNR—Molecular Cloud Interactions

AbstractSpectroscopic imaging of the SNR RCW 103 has revealed extensive emission in near-infrared lines of H2and [Fe II], where the blast wave is encountering a molecular cloud. The H2 appears to be located outside the [FeII], a morphology which challenges our understanding of shock wave physics. It is suggested that reverse shocks may be responsible for the phenomenom.

New approaches for developing high-performance solid-dynamic simulation systems

Large solid-dynamic shock-wave physics simulations pose a difficult challenge to current shared-memory vector supercomputer capabilities. Massively parallel computing promises to provide the brute compute power to dramatically reduce the time needed to perform these simulations. However, many software developers foresee a future customer base with access to a wide variety of parallel computing platforms. A major challenge will be to build, at an acceptable cost, a high-performance simulation software environment which can effectively utilize serial, vector and parallel machines of various types. In an era of increased competitiveness, every means must be found to improve quality and decrease both development and maintenance costs. Developing and maintaining large scientific software systems using FORTRAN technology may not be the optimal solution for all developers. Software technologies such as the object-oriented language, C++, provide an opportunity to develop scientific simulation systems in a robust software engineering environment. Such systems, if well designed, have excellent portability and are easily optimized for a variety of architectures. In addition many scientific software developers are looking to commercially available software components to provide improved productivity and quality. Many of these well-designed software toolkits are or will be written in C++. CTH is a major production solid-dynamics simulation code developed by Sandia National Laboratories. The code is used extensively by other government laboratories and contractors. It was originally written in FORTRAN 77 with a focus on performance for the CRAY shared-memory vector architecture. A next generation code, parallel CTH (PCTH), is currently being developed for serial, vector and massively parallel computers with a major emphasis on portability and the utilization of commercially available software components for database generation and graphics. Major portions of the PCTH system are written in the object-oriented language C++. Trade-offs and considerations for developing scientific software in an object-oriented software environment are discussed.

Shock-wave equation-of-state studies at Los Alamos

A history of the shock-wave equation-of-state (EOS) studies at Los Alamos is given. Particular emphasis is placed on the pioneering research in the 1950s where many of the experimental techniques and methods of analysis were developed, which we now take for granted. A brief review of shock-wave physics is given, which illustrates important hydrodynamic and thermodynamic concepts. Recent studies on the EOS of Ti are presented with emphasis on theα-to-ω phase transition. VISAR wave profiles for polycrystalline Ni and singlecrystal Ni are presented to determine the strengths of these materials under pressure. Low-density polystyrene foam Hugoniot experiments are described and results analyzed.

Shock Wave Physics

Extracorporeal shock wave lithotripsy has significantly altered the management of symptomatic renal and ureteral calculi. Yet in an effort to limit the potentially harmful effects of shock waves, while still maintaining or maximizing stone fragmentation, one must understand basic shock wave physics. This report presents a brief overview of the physical properties of shock waves and describes three different areas of shock wave physics investigation: measurement of shock wave pressures, assessment of stone fragmentation, and development of a stone phantom to allow the comparison of various lithotripsy devices. It is only through additional study of the basic physics of high-energy shock waves that we will be able to further enhance the clinical benefits of extracorporeal shock wave lithotripsy. Further understanding of the individual characteristics of a shock wave pressure field such as peak positive pressure, peak negative pressure, pulse duration, and size/shape of the focal region will allow the subsequent enhancement of stone fragmentation while minimizing the potential for shock wave injury to surrounding tissues.

History and prospects of shock wave physics

History and prospects of shock wave physics

CTH: A three-dimensional shock wave physics code

CTH is a software system under development at Sandia National Laboratories Albuquerque to model multidimensional, multi-material, large deformation, strong shock wave physics. One-dimensional recti-linear, cylindrical, and spherical meshes; two-dimensional rectangular, and cylindrical meshes; and three-dimensional rectangular meshes are currently available. A two-step Eulerian solution scheme is used with these meshes. The first step is a Lagrangian step in which the cells distort to follow the material motion. The second step is a remesh step where the distorted cells are mapped back to the Eulerian mesh. CTH has several models that are useful for simulating strong shock, large deformation events. Both tabular and analytic equations of state are available. CTH can model elastic-plastic behavior, high explosive detonation, fracture, and motion of fragments smaller than a computational cell. The elastic-plastic model is elastic-perfectly plastic with thermal softening. A programmed burn model is available for modelling high explosive detonation. The Jones-Wilkins-Lee equation of state is available for modelling high explosive reaction products. Fracture can be initiated based on pressure or principle stress. A special model is available for moving fragments smaller than a computational cell with statistically the correct velocity. This model is very useful for analyzing fragmentation experiments and experiments with witness plates. CTH has been carefully designed to minimize the dispersion present in Eulerian codes. It has a high-resolution interface tracker that prevents breakup and distortion of material interfaces. It uses second order convection schemes to flux all quantities between cells. This paper describes the models, and novel features of CTH. Special emphasis will be placed on the features that are novel to CTH or are not direct generalizations of two-dimensional models. Another paper by Trucano and McGlaun (1989) describes several hypervelocity impact calculations using CTH.

Hypervelocity impact calculations using CTH: Case studies

In this paper, we discuss the use of the CTH shock wave physics code in the calculation of hypervelocity impact phenomena. We emphasize unusual features of the code that aid in understanding the sensitivity of hypervelocity impact calculations to the numerical methodology. A canonical type of impact problem in which a debris cloud is generated and stagnates against a secondary structure is analyzed. We then provide examples of the contributions of advection, interface tracking, and equation of state (EOS) algorithms to CTH simulations of this type of impact, and comment on grid resolution issues. A general conclusion is that while grid resolution is the dominant source of error in the impact simulations, issues related to advection, interface tracking, and EOS are of comparable importance. We also present examples of the application of CTH to 3-D impact problems, illustrating the potential of 3-D computation, and the severe demands it places on current generation computing hardware.

Subnanosecond x-ray diffraction from laser-shocked crystals.

We have used single-shot sub-nanosecond x-ray diffraction to directly measure lattice parameters of crystals during the passage of laser-driven shock waves. Changes in the interatomic spacings can be measured with a temporal resolution better than 50 ps. We have studied shock-launching in single crystals and have directly measured dynamic tension during shock-breakout from a rear surface. In separate experiments we have directly observed the onset of shock-induced plasticity by diffracting from planes running perpendicular to the shock front. In addition to the single crystal work we have recently demonstrated that we can record x-ray powder patterns with sub-nanosecond exposure times; and are now in a position to laser-shock polycrystalline material simultaneously with the x-ray flash. The technique promises to be useful in the study of many fundamental problems in shock wave physics, including the behaviour of materials at the lattice level during plastic deformation and shock-induced polymorphic phase transitions.

On the transition from a waveless to a wavy interface in explosive welding

An analysis and critique are presented of the hydrodynamic theory for wave formation in explosive welding, as proposed by Cowan et al. Based on the recent advances in the understanding of this domain, the above-mentioned study is seen to support a different mechanism, dynamic plasticity, to explain wave generation at the interface of explosively welded couples. The transition from a waveless to a wavy interface was studied by means of impact welding for three different systems (CuCu, FeFe and AlAl). It was found that this transition is dependent on the collision angle and can be expressed by means of an elastic-plastic constant, based on the static properties of the materials. The criterion developed here can be extended to determine the waveless to wavy transition velocity for any system. The necessity for the development of a mathematical model that includes shock wave physics of the phenomena to explain the pulsating pressure instability and wave generation is also emphasized.

Some associations of J. C. Jamieson with the shock wave community

A brief review is presented of some of the things John Jamieson did while working with people involved with shock wave physics and equation of state at high pressure. This also includes work done on geophysical problems and equation‐of‐state problems that might not be included in the review articles published in this issue. The subjects covered are some recovery work, studies on rutile and rutile structures, gold standard, flash X ray crystal studies of shocked metals, volume effects on the Gruneisen parameter, equation of state of oxygen, and measurement of Poisson's ratio at high pressure. Although most of these topics are not all directly related to shock wave studies, they all were things that the people working in shock wave physics were also investigating or were directly involved with John in his studies.

Interferometric laser technique for accurate velocity measurement in shock wave physics

An interferometric system for continuously measuring specimen velocity is described. The Döppler shift of a laser beam reflected from the specimen’s free surface is transformed into a variation of the diameter of Fabry–Perot interference rings, and the evolution of the diameter versus time is continuously recorded by a streak camera. Two examples of the use of this system for study of shock waves are given to show the accuracy of this device.

Physics of a wall-confined fusion system

To understand plasma phenomena which will occur in a wall-confined, shock-heated fusion system, experiments and computer simulations have been carried out. The thermonuclear fusion cycle, energy transfer from a β > 1 hot plasma to a wall, plasma confinement by means of walls and a magnetic dam, and some new strong shock wave physics results are described and reviewed.