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RADIOGRAPHIC RESULTS FROM THE NTLX SERIES OF HYDRODYNAMIC EXPERIMENTS

Description: The NTLX series of experiments are focused on measuring the shock induced hydrodynamic flow of a Sn-PMMA target. For these experiments multi-frame flash X-ray radiography is used to measure the position of the Sn-PMMA target interface and the location of shock in the PMMA as a function of time. Four radiographs are acquired at 700 ns intervals having a line-of-sight following the target's axis of symmetry. Because the X-ray spectrum from the sources has an end-point energy of {approx}300 keV with a strong component of {approx}60 keV tungsten K-line radiation, the Sn portion of the target is radiographically opaque. However, X-rays are transmitted through the PMMA portion of the target thereby allowing motion of the Sn-PMMA interface to be imaged. Also, the shock location is tracked as a function of time due to the density increase in the shocked PMMA. The resulting radiographs are analyzed to provide the trajectory and shape of both the shock and Sn-PMMA interface. In addition, the shock velocity in the Sn is determined for asymmetric target geometries.
Date: June 1, 2001
Creator: OLSON, R.T.; ORO, D.M. & AL, ET
Partner: UNT Libraries Government Documents Department

A flash x-ray system for diagnosing liner implosions

Description: This paper describes a low energy flash X-ray system that is ideal for radiographing a wide variety of experimental phenomenon on both capacitor-bank pulsed power facilities and explosively driven magnetic-flux compression experiments. The versatility of this system has allowed us to obtain both single X-radiographs of imploding liners and multiple, temporally resolved radiographic sequences of target evolution. The dynamic liner radiographs are acquired with radially oriented X-ray heads that are instrumental for observing and diagnosing liner shape and symmetry, Rayleigh-Taylor instability growth, and liner-glide plane interaction (see Fig. 1). Multiframe radiographs acquired along the axis of a cylindrical target are used to provide physical data on phenomena such as shock-driven target hydrodynamics, Richtmyer-Meshkov instability growth, spall, fiction, and equations of state. The flexibility of this X-ray system has also allowed it to be successfully fielded both at various gas and powder gun facilities and explosively driven shock physics experiments.
Date: January 1, 2003
Creator: Anderson, B. G. (Brodie G.); Oro, D. M. (David M.); Olson, R. T. (Russell T.); Studebaker, J. K. (Jan K.) & Platts, D. (David)
Partner: UNT Libraries Government Documents Department

Material Failure and the Growth of Instabilities in Hollow Cylindrical Samples of Aluminum Shocked to 14Gpa and 50Gpa (U)

Description: Understanding the surface stability of metals undergoing dynamic fracture at shock breakout is important to several applications in metals processing. The advantages of using the Pegasus II facility to investigate the phenomena occurring at shock break out are described. As an example of the data collected, we concentrate on brief descriptions of two experiments that compared the tensile failure, i.e. ''spall'', patterns in the presence of sinusoidal perturbations seeded on the free inner surface of cylindrical samples made of structural grade Al 6061.T6. These samples were subjected to ramped waves with shock pressures of 14 GPa and 50 GPa to observe the effect of pressure on the production of a type of volumetric failure that is mentioned here ''microspall.'' This failed region behind the exiting surface of the shock wave is comprised of a significant volume of low-density, probably granular, material. The failure mechanism, combined with the forces that cause inertial instability, leads to rapid pattern growth in the failed material, observable as density variations, as well as to pattern growth on the surface. Pattern growth was observed to vary with perturbation amplitude, wavelength, and shock pressure. Both increased pressure and increased amplitude were shown to destabilize a stable perturbation. Increasing the wavelength by a factor of 3 was shown to result in significantly slower growth of the pattern within the failed volume. The mechanisms leading to the formation of the spall volume and to the patterns are discussed briefly.
Date: November 20, 1999
Creator: Stokes, J.; Fulton, R.D.; Morgan, D.V.; Obst, A.W.; Oro, D.M.; Oona, H. et al.
Partner: UNT Libraries Government Documents Department

Nonlinear response of the photocathode of an x-ray streak camera to UV light

Description: We have found that a potassium-iodide photocathode of an x-ray streak camera responds to UV light at {lambda}=308 nm. The photocathode surface work function, 6.5 eV, is larger than the 4 eV energy of the UV photon, hence the source of the response is interesting. We will present results on the response of a transmission type potassium-iodide photocathode to the UV light from a {lambda}308 nm, subpicosecond XeCl laser and from a {lambda}=326 nm HeCd laser. We will test for the nonlinearity of the yield to measure of the number of photons that are needed to be absorbed before a signal is recorded. We will present data on the effect of the UV irradiance on the yield, as well as on the temporal width of the recorded signal. We will give an explanation of the observation and its effect on the dynamic-range response of the streak-camera. We will show that the response is linear with the incident irradiance, up to an incident irradiance of 10{sup 8} W/cm{sup 2} and we will explain the observation.
Date: September 1, 1994
Creator: Kyrala, G. A.; Oro, D. M.; Studebaker, J. K.; Wood, W. M.; Schappert, G. T.; Watts, S. et al.
Partner: UNT Libraries Government Documents Department

Radiographic results from the NTLX series of hydrodynamic experiments

Description: The NTLX series of experiments are focused on measuring the shock induced hydrodynamic flow of a Sn-PMMA target. For these experiments multi-frame flash X-ray radiography is used to measure the position of the Sn-PMMA target interface and the location of shock in the PMMA as a function of time. Four radiographs are acquired at 700 ns intervals having a line-of-sight following the target's axis of symmetry. Because the Xray spectrum from the sources has an end-point energy of {approx}300 keV with a strong component of {approx}60 keV tungsten K-line radiation, the Sn portion of the target is radiographically opaque. However, X-rays are transmitted through the PMMA portion of the target thereby allowing motion of the Sn-PMMA interface to be imaged. Also, the shock location is tracked as a function of time due to the density increase in the shocked PMMA. The resulting radiographs are analyzed to provide the trajectory and shape of both the shock and Sn-PMMA interface. In addition, the shock velocity in the Sn is determined for asymmetric target geometries.
Date: January 1, 2001
Creator: Olson, R. T. (Russell T.); Oro, D. M. (David M.); Anderson, B. G. (Brodie G.); Studebaker, J. K. (Jan K.); Alvey, K. (Ken); Peterson, K. (Ken) et al.
Partner: UNT Libraries Government Documents Department

A Pegasus Dynamic Liner Friction Experiment

Description: The authors report on a pulsed power experiment performed at the Los Alamos National Laboratory Pegasus facility which was designed to measure material flow at metal interfaces driven to high relative velocities. Material motion at and near four flat Ta/Al(6061) interfaces was measured using flash radiographic techniques. A series of fine Pb wires (407 micron diameter) was implanted in the Al normal to the interfaces. The motion of these markers under shock loading provided a picture of material motion in the Al interfacial region. The surface roughness of the interfaces was varied between 32 and 125 micro-inches. The authors discuss the implications of these measurements for constitutive models of high speed friction and interfacial morphological change.
Date: June 28, 1999
Creator: Hammerberg, J.E.; Kyrala, G.A.; Oro, D.M.; Fulton, R.D.; Anderson, W.E.; Obst, A.W. et al.
Partner: UNT Libraries Government Documents Department

Application of the Pegasus II Pulsed-Power Facility to the Study of Inertial Instability and Fracture of Cylindrical Tubes of Solid Aluminum

Description: Understanding the surface stability of metals undergoing dynamic fracture at shock breakout is important to several applications in metals processing. The advantages of using the Pegasus II facility to investigate the phenomena occurring at shock break out are described. As an example of the data collected, we concentrate on brief descriptions of two experiments that compared the tensile failure, i.e. ''spall'', patterns in the presence of sinusoidal perturbations seeded on the free inner surface of cylindrical samples of 3 types of Al. These samples were composed variously of soft Al 1100-O, structural grade Al 6061-T6, and ultra-pure 99.99% Al and were subjected to Taylor waves with shock pressures of 14 GPa. We show that the material behind the exiting surface undergoes a type of failure termed here ''microspall'', resulting in the production of a significant volume of low-density, probably granular, material. The failure mechanism, combined with the forces that cause inertial instability, leads to rapid pattern growth in the failed material and subsequent pattern growth on the surface. Pattern growth was studied as a function of perturbation wavelength and amplitude. The different Al samples vary by an order of magnitude in yield strength, and some increase in pattern instability was observed at lower yield strength. The ultra-pure Al has exceptionally large grain size, in the mm range. No appreciable variation of spall pattern was observed due to grain size.
Date: June 23, 1999
Creator: Chandler, E.A.; Stokes, J.; Fulton, R.D.; Morgan, D.V.; Obst, A.W.; Oro, D.M. et al.
Partner: UNT Libraries Government Documents Department

First beam at DARHT-II

Description: The second axis of the Dual Axis Radiographic Hydro-Test (DARHT) facility will provide up to four short (<100 ns) radiation pulses for flash radiography of high-explosive driven implosion experiments. To accomplish this the DARHT-I1 linear induction accelerator (LIA) will produce a 2-kA electron beam with 18-MeV kinetic energy, constant to within 2 0.5% for 2-ps. A fast kicker will cleave four short pulses out of the 2-ps flattop, with the bulk of the beam diverted into a dump. The short pulses will then be transported to the final-focus magnet, and focused onto a tantalum target for conversion to bremsstrahlung pulses for radiography. DARHT-II is a collaborative effort between Los Alamos, Livermore, and Berkeley National Laboratories. The first tests of the second axis accelerator, described herein, were performed to demonstrate the technology and to meet the performance requirements for closing out the DARHT-II construction project.
Date: January 1, 2003
Creator: Ekdahl, C. A. (Carl A.); Abeyta, E. O. (Epifanio Orlando); Caudill, L. D. (Larry D.); Dalmas, D. A. (Dale Allen); Eversole, S. A. (Steven A.); Harrison, J. F. (James F.) et al.
Partner: UNT Libraries Government Documents Department

Spall experiments in convergent geometry using the atlas pulsed power facility.

Description: {sm_bullet}Four spall experiments have been performed using Atlas {sm_bullet} Purpose was to investigate damage in convergent geometry {sm_bullet} Impact pressures ranged between 45 kbars - 110 kbars {sm_bullet} Diagnostics included VISAR and axial and radial radiographs {sm_bullet} Targets were recovered for post-metallugical analysis
Date: January 1, 2002
Creator: Keinigs, R. K. (Rhonald K.); Anderson, W. A. (William A.); Cerreta, E. K. (Ellen K.); Cochrane, J. C. (James C.), Jr.; Ladish, J. S. (Joseph S.); Lindemuth, I. R. (Irvin R.) et al.
Partner: UNT Libraries Government Documents Department

Ranchero Explosive Pulsed Power Experiments

Description: The authors are developing the Ranchero high explosive pulsed power (HEPP) system to power cylindrically imploding solid-density liners for hydrodynamics experiments. The near-term goal is to conduct experiments in the regime pertinent to the Atlas Capacitor bank. That is, they will attempt to implode liners of {approximately}50 g mass at velocities approaching 15 km/sec. The basic building block of the HEPP system is a coaxial generator with a 304.8 mm diameter stator, and an initial armature diameter of 152 mm. The armature is expanded by a high explosive (HE) charge detonated simultaneously along its axis. They have reported a variety of experiments conducted with generator modules 43 cm long and have presented an initial design for hydrodynamic liner experiments. In this paper they give a synopsis of their first system test, and a status report on the development of a generator module that is 1.4 m long.
Date: June 27, 1999
Creator: Goforth, J.H.; Atchison, W.L.; Deninger, W.J.; Fowler, C.M.; Herrera, D.H.; King, J.C. et al.
Partner: UNT Libraries Government Documents Department

Material science experiments on the Atlas Facility

Description: Three material properties experiments that are to be performed on the Atlas pulsed power facility are described; friction at sliding metal interfaces, spallation and damage in convergent geomety, and plastic flow at high strain and high strain rate. Construction of this facility has been completed and experiments in high energy density hydrodynamics and material dynamics will begin in 2001.
Date: January 1, 2001
Creator: Keinigs, R. K. (Rhonald K.); Atchison, W. L. (Walter L.); Faehl, R. J. (Rickey J.); Lindemuth, I. R. (Irvin R.); Anderson, W. E. (Wallace E.); Bartsch, R. R. (Robert Richard) et al.
Partner: UNT Libraries Government Documents Department