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Use of Z-pinch sources for high-pressure shock wave studies

Description: In this paper, we will discuss the use of z-pinch sources for shock wave studies at multi-Mbar pressures. Experimental plans to use the technique for absolute shock Hugoniot measurements are discussed. Recent developments have demonstrated the use of pulsed power techniques for producing intense radiation sources (Z pinches) for driving planar shock waves in samples with spatial dimensions significantly larger than possible with other radiation sources. Initial indications are that using Z pinch sources for producing Planckian radiation sources in secondary hohlraums can be used to drive shock waves in samples with diameters to a few millimeters and thickness approaching one millimeter in thickness. These dimensions provides the opportunity to measure both shock velocity and the particle velocity behind the shock front with accuracy comparable to that obtained with gun launchers. In addition, the peak hohlraum temperatures of nearly 150 eV that are now possible with Z pinch sources result in shock wave pressures approaching 45 Mbar in high impedance materials such as tungsten and 10-15 Mbar in low impedance materials such as aluminum and plastics. In this paper, we discuss the use of Z pinch sources for making accurate absolute EOS measurements in the megabar pressure range.
Date: January 1, 1998
Creator: Konrad, C.H.; Asay, J.R. & Hall, C.A.
Partner: UNT Libraries Government Documents Department

Use of z-pinch sources for high-pressure shock wave experiments

Description: Recent developments have demonstrated the use of pulsed power for producing intense radiation sources (z-pinches) that can drive planar shock waves in samples with spatial dimensions significantly larger than possible with other radiation sources. In this paper, the authors will discuss the use of z-pinch sources for shock wave studies at multi-Mbar pressures. Experimental plans to use the technique for absolute shock Hugoniot measurements and with accuracies comparable to that obtained with gun launchers are discussed.
Date: August 1, 1997
Creator: Konrad, C.H.; Trott, W.M. & Hall, C.A.
Partner: UNT Libraries Government Documents Department

Analysis of Radiation-Driven Explosive Flyers

Description: There is great interest in being able to use the x-ray output from a Z-pinch for equation of state measurements at extreme conditions. However, the direct x-ray output form the pinch produces a very sharp and rapidly attenuating pressure pulse in target materials. To obtain high quality measurements with this source, a mechanism for generating non-attenuating waves is needed. One possibility involves using the x-ray source to throw a near-normal density intermediate drive at the target, a situation similar to more conventional configurations. To scope out preliminary design parameters, they used the ALEGRA code to simulate a number of different possibilities involving the driver and the gap between it and the target. They used a somewhat idealized radiation source--a main x-ray pulse 30 ns long at its base and peaking at a blackbody temperature of 100 eV. The calculations suggest that a 100-micron aluminum driver with a 90-micron gap will yield a 15-ns-wide non-attenuating pulse with an amplitude of over 250 GPa.
Date: July 19, 1999
Creator: Lawrence, R.J.; Asay, J.R.; Trucano, T.G. & Hall, C.A.
Partner: UNT Libraries Government Documents Department

Thermal and electrostrictive expansion characteristics of MLC (Multilayer Ceramic) capacitors

Description: We have measured by strain gauge technique, in-plane thermal expansivity (coefficient of thermal expansion) as a function of temperature and electrostrictive expansion as a function of applied DC voltage for ceramic capacitors with X7R, NPO and N1500 dielectrics. Multilayer Ceramic (MLC) capacitor materials from two commercial suppliers were evaluated. Thermal expansivities of these materials were compared to polyimide-quartz boards and alumina ceramic substrates. 4 refs., 9 figs., 1 tab.
Date: January 1, 1991
Creator: Chanchani, R. & Hall, C.A.
Partner: UNT Libraries Government Documents Department

Optical Spectroscopy Measurements of Shock Waves Driven by Intense Z-Pinch Radiation

Description: Z-pinches created using the Z accelerator generate {approximately}220 TW, 1.7 MJ radiation pulses that heat large ({approximately}10 cm{sup 3}) hohlraums to 100-150 eV temperatures for times of order 10 nsec. We are performing experiments exploiting this intense radiation to drive shock waves for equation of state studies. The shock pressures are typically 1-10 Mbar with 10 nsec duration in 6-mm-diameter samples. In this paper we demonstrate the ability to perform optical spectroscopy measurements on shocked samples located in close proximity to the z-pinch. These experiments are particularly well suited to optical spectroscopy measurements because of the relatively large sample size and long duration. The optical emission is collected using fiber optics and recorded with a streaked spectrograph. Other diagnostics include VISAR and active shock breakout measurements of the shocked sample and a suite of diagnostics that characterize the radiation drive. Our near term goal is to use the spectral emission to obtain the temperature of the shocked material. Longer term objectives include the examination of deviations of the spectrum from blackbody, line emission from lower density regions, determination of kinetic processes in molecular systems, evaluation of phase transitions such as the onset of metalization in transparent materials, and characterization of the plasma formed when the shock exits the rear surface. An initial set of data illustrating both the potential and the challenge of these measurements is described.
Date: April 9, 1999
Creator: Asay, J. Bernard, M.; Bailey, J.E.; Carlson, A.L.; Chandler, G.A.; Hall, C.A.; Hanson, D. et al.
Partner: UNT Libraries Government Documents Department

Z-Pinch Driven Isentropic Compression for Inertial Fusion

Description: The achievement of high gain with inertial fusion requires the compression of hydrogen isotopes to high density and temperatures. High densities can be achieved most efficiently by isentropic compression. This requires relatively slow pressure pulses on the order of 10-20 nanoseconds; however, the pressure profile must have the appropriate time. We present 1-D numerical simulations that indicate such a pressure profile can be generated by using pulsed power driven z pinches. Although high compression is calculated, the initial temperature is too low for ignition. Ignition could be achieved by heating a small portion of this compressed fuel with a short (-10 ps) high power laser pulse as previously described. Our 1-D calculations indicate that the existing Z-accelerator could provide the driving current (-20 MA) necessary to compress fuel to roughly 1500 times solid density. At this density the required laser energy is approximately 10 kJ. Multidimensional effects such as the Rayleigh-Taylor were not addressed in this brief numerical study. These effects will undoubtedly lower fuel compression for a given chive current. Therefore it is necessary to perform z-pinch driven compression experiments. Finally, we present preliminary experimental data from the Z-accelerator indicating that current can be efficiently delivered to appropriately small loads (- 5 mm radius) and that VISAR can be used measure high pressure during isentropic compression.
Date: February 1, 1999
Creator: Asay, J.R.; Hall, C.A.; Holland, K.G.; Slutz, S.A.; Spielman, R.B. & Stygar, W.A.
Partner: UNT Libraries Government Documents Department

Use of Z-pinch radiation sources for high-pressure shock wave studies

Description: The authors are developing a new shock wave diagnostic using Z pinch sources for high-pressure equation of state (EOS) measurements. Specifically, they are employing VISAR interferometry to measure the particle velocity of shocked materials and fiber optic probes to measure the shock speed. Combination of these measurements will allow absolute EOS data with Z accelerators. This report is a progress report on the development of this new approach to EOS measurements; however, preliminary data obtained with the diagnostics are encouraging. With further development of Z pinch sources, it is envisioned that a variety of EOS and constitutive property measurements can be made. Time-resolved wave profile measurements will then provide a variety of EOS and material property data, such as isentropic EOS, initial compressive strength and shock-induced compressive strength, dynamic tensile strength, kinetics of phase transitions, and surface stability studies.
Date: August 1998
Creator: Asay, J. R.; Konrad, C. H.; Hall, C. A.; Trott, W. M.; Chandler, G. A.; Fleming, K. J. et al.
Partner: UNT Libraries Government Documents Department

Shock Hugoniot and release states in concrete mixtures with different aggregate sizes from 3 to 23 GPa

Description: A series of controlled impact experiments has been performed to determine the shock loading and release behavior of two types of concrete, differentiated by aggregate size, but with average densities varying by less than 2 percent. Hugoniot stress and subsequent release data was collected over a range of approximately 3 to 25 GPa using a plate reverberation technique in combination with velocity interferometry. The results of the current data are compared to those obtained in previous studies on concrete with a different aggregate size but similar density. Results indicate that the average loading and release behavior are comparable for the three types of concrete discussed in this paper.
Date: September 1, 1997
Creator: Hall, C. A.; Chhabildas, L. C. & Reinhart, W. D.
Partner: UNT Libraries Government Documents Department

Use of Z pinch radiation sources for high pressure shock wave studies

Description: Recent developments in pulsed power technology demonstrate use of intense radiation sources (Z pinches) for driving planar shock waves in samples with spatial dimensions larger than possible with other radiation sources. Initial indications are that the use of Z pinch sources can be used to produce planar shock waves in samples with diameters of a few millimeters and thicknesses approaching one half millimeter. These dimensions allow increased accuracy of both shock velocity and particle velocity measurements. The Z pinch radiation source uses imploding metal plasma induced by self-magnetic fields applied to wire arrays to produce high temperature x-ray environments in vacuum hohlraum enclosures. Previous experiments have demonstrated that planar shock waves can be produced with this approach. A photograph of a wire array located inside the vacuum hohlraum is shown here. Typically, a few hundred individual wires are used to produce the Z pinch source. For the shock wave experiments being designed, arrays of 120 to 240 tungsten wires with a diameter of 40 mm and with individual diameters of about 10 {micro}m are used. Preliminary experiments have been performed on the Z pulsed radiation source to demonstrate the ability to obtain VISAR measurements in the Z accelerator environment. Analysis of these results indicate that another effect, not initially anticipated, is an apparent change in refractive index that occurs in the various optical components used in the system. This effect results in an apparent shift in the frequency of reflected laser light, and causes an error in the measured particle velocity. Experiments are in progress to understand and minimize this effect.
Date: August 1, 1998
Creator: Asay, J.R.; Konrad, C.H.; Hall, C.A.; Trott, W.M.; Chandler, G.A.; Holland, K.G. et al.
Partner: UNT Libraries Government Documents Department

The "Z" Pulsed Radiation Source: Recent Developments in Equation of State Measurement Capabilities

Description: The Sandia Z machine is a source of intense radiation which can be used to drive ablative shocks for equation of state studies. In developing the capability to diagnose these types of studies on Z, techniques commonly used in conventional impact generated experiments were leveraged. The primary diagnostic transferred was velocity interferome~, VLSAR, [1] which not only provides Hugoniot particle velocity measurements, but also indications of shock stability and wave attenuation. In addition to a VISAR capability on the Z machine, methods for measuring shock velocity have been developed. When these measured parameters are used in conjunction with the Rankine-Hugoniot jump conditions, [2] material response at high temperatures and pressures can be inferred. With sample sizes used on Z being much smaller than those fielded in typical impact experiments, temporal resolution and methods of interfacing the diagnostics with the targets had to be improved. In this paper, a "standard" equation of state experiment, associated diagnostics, and some recent results in aluminum and beryllium will be discussed.
Date: October 13, 1998
Creator: Asay, J.R.; Chandler, G.; Clark, B.; Fleming, K.; Hall, C.A.; Holland, K. et al.
Partner: UNT Libraries Government Documents Department

Z: A Fast Pulsed Power Generator for Ultra-High Magnetic Field Generation

Description: Advances in fast, pulsed-power technologies have resulted in the development of very high current drivers that have current rise times - 100 ns. The largest such pulsed power drive r today is the new Z accelerator located at Sandia National Laboratories in Albuquerque, New Mexico. Z is capable of delivering more than 20 MA with a time-to-peak of 105 ns to low inductance (- 1 nH)loads. Such large drivers are capable of directly generating magnetic fields approaching 3 kT in small, 1 -cm3, volumes. In addition to direct field generation, Z can be used to compress an applied, axial seed field with a plasma. Flux compression scheme~: are not new and are, in fact, the basis of all explosive flux-compression generators but we propose the use of plasma armatures rather than solid, conducting armatures. We will present experimental results from the Z accelerator in which magnetic fields - 2 kT are generated and measured with several diagnostics. Issues such as energy loss in solid conductors and dynamic response of current-carrying conductors to very large magnetic fields will be reviewed in context with Z experiments. We will describe planned flux-compression experiments that are expected to create the highest-magnitude uniform-field volumes yet attained in the laboratory.
Date: November 4, 1998
Creator: Asay, J.R.; Bailey, J.E.; Bernard, M.A.; Hall, C.A.; McDaniel, D.H.; Spielman, R.B. et al.
Partner: UNT Libraries Government Documents Department

Isentropic Compression of LX-04 on the Z Accelerator

Description: Three sets of LX-04 samples of 0.18 and 0.49 mm nominal thicknesses were all dynamically loaded by Sandia's Z-accelerator with a ramp compression wave with a 200 ns rise time and about 150 kb peak stress. The LX-04/lithium fluoride samples interface velocities were measured using VISAR's. Comparisons of experimental and computational results will be given. Compression and release isentropes both show some reaction and kinetic behavior of the LX-04. Experiments were also performed on fine-grained TATB. Future experiments on single crystals of HMX that are designed to measure the phase transition at high pressures will be discussed.
Date: June 7, 2001
Creator: Reisman, D.B.; Forbes, J.W.; Tarver, C.M.; Garcia, F.; Cauble, R.C.; Hall, C.A. et al.
Partner: UNT Libraries Government Documents Department

MHD Modeling of Conductors at Ultra-High Current Density

Description: In conjunction with ongoing high-current experiments on Sandia National Laboratories' Z accelerator, the authors have revisited a problem first described in detail by Heinz Knoepfel. Unlike the 1-Tesla MITLs of pulsed power accelerators used to produce intense particle beams, Z's disc transmission line (downstream of the current addition) is in a 100--1,200 Tesla regime, so its conductors cannot be modeled simply as static infinite conductivity boundaries. Using the MHD code MACH2 they have been investigating the conductor hydrodynamics, characterizing the joule heating, magnetic field diffusion, and material deformation, pressure, and velocity over a range of current densities, current rise-times, and conductor materials. Three purposes of this work are (1) to quantify power flow losses owing to ultra-high magnetic fields, (2) to model the response of VISAR diagnostic samples in various configurations on Z, and (3) to incorporate the most appropriate equation of state and conductivity models into the MHD computations. Certain features are strongly dependent on the details of the conductivity model.
Date: August 29, 2000
Creator: ROSENTHAL,STEPHEN E.; DESJARLAIS,MICHAEL P.; SPIELMAN,RICK B.; STYGAR,WILLIAM A.; ASAY,JAMES R.; DOUGLAS,M.R. et al.
Partner: UNT Libraries Government Documents Department

Isentropic Compression of Iron with the Z Accelerator

Description: Development of isentropic loading techniques is a long standing goal of the shock physics community. The authors have used the Sandia Z Accelerator to produce smoothly increasing pressure loading on planar iron specimens over time durations of 100 ns and for pressures to 300 Mbar. Free surface velocity measurements on the rear surface of the continuously loaded specimens were made on specimens 0.5-mm and 0.8-mm thick and clearly show the effects of wave evolution into the well known two-wave structure resulting from the {alpha}-{var_epsilon} phase transition beginning at 125 kbar. The resulting wave profiles are analyzed with a rate-dependent, phase transition model to extract information on phase transformation kinetics for isentropic compression of iron. Comparison of the experiments and calculations demonstrate the value of isentropic loading for studying phase transition kinetics.
Date: June 10, 1999
Creator: Asay, J.R.; Bernard, M.A.; Hall, C.A.; Hayes, D.B.; Holland, K.G.; McDaniel, D.H. et al.
Partner: UNT Libraries Government Documents Department

Use of Z-Pinch Techniques for Equation of State Applications

Description: A principal goal of the shock physics program at Sandia is to establish a capability to make accurate equation of state (EOS) measurements on the Z pulsed radiation source. The Z accelerator is a source of intense x-ray radiation, which can be used to drive ablative shocks for EOS studies. With this source, ablative multi shocks can be produced to study materials over the range of interest to both weapons and ICF physics programs. In developing the capability to diagnose these types of studies on Z, techniques commonly used in conventional impact generated experimental were implemented. The primary diagnostic presently being used for this work is velocity interferometry, VISAR, which not only provides Hugoniot particle velocity measurements, but also measurements of non-shock EOS measurements, such as isentropic compression. In addition to VISAR capability, methods for measuring shock velocity have also been developed for shock studies on Z. When used in conjunction with the Rankine- Hugoniot jump conditions, material response at high temperatures and pressures can be inferred. Radiation in the Z accelerator is produced when approximately 18 MA are passed through a cylindrical wire array typically 20 to 50 mm in diameter and 10 to 20 mm in height. 200-300 wires with initial diameters on the order of 8 to 20 micron form, upon application of the current, a plasma shell, which is magnetically imploded until it collapses and stagnates on axis, forming a dense plasma emitter in the shape of a column, referred to as a" z pinch". The initial wire array and subsequent plasma pinch are confined within a metallic can, referred to as a primary hohlraum, which serves as both a current return path and a reflective surface to contain the radiation. Attached to openings in the primary hohlraum wall are smaller tubes referred to as secondaries. ...
Date: November 11, 1998
Creator: Asay, J.R.; Bernard, M.A.; Clark, B.; Fleming, K.J.; Hall, C.A.; Hauer, A. et al.
Partner: UNT Libraries Government Documents Department

MHD Modeling of Conductors at Ultra-High Current Density

Description: In conjunction with ongoing high-current experiments on Sandia National Laboratories' Z accelerator we have revisited a problem first described in detail by Heinz Knoepfel. MITLs of previous pulsed power accelerators have been in the 1-Tesla regime. Z's disc transmission line (downstream of the current addition) is in a 100-1200 Tesla regime, so its conductors cannot be modeled simply as static infinite conductivity boundaries. Using the MHD code MACH2 we have been investigating conductor hydrodynamics, characterizing the joule heating, magnetic field diffusion, and material deformation, pressure, and velocity over a range of current densities, current rise-times, and conductor materials. Three purposes of this work are ( 1) to quantify power flow losses owing to ultra-high magnetic fields, (2) to model the response of VISAR diagnostic samples in various configurations on Z, and (3) to incorporate the most appropriate equation of state and conductivity models into our MHD computations. Certain features are strongly dependent on the details of the conductivity model. Comparison with measurements on Z will be discussed.
Date: June 30, 1999
Creator: Asay, J.R.; Desjarlais, M.P.; Douglas, M.R.; Frese, M.H.; Hall, C.A.; Morse, R.L. et al.
Partner: UNT Libraries Government Documents Department