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Z-pinch diagnostics, plasma and liner instabilities and new x-ray techniques

Description: Pulse power experiments of the last several decades have contributed greatly to the understanding of high temperature and high density plasmas and, more recently, to the study of hydrodynamic effects in thick imploding cylinders. Common to all these experiments is the application of a large current pulse to a cylindrically symmetric load, with the resulting Lorenz force compressing the load to produce hydrodynamic motion and/or high temperature, high density plasma. In Los Alamos, Pulsed power experiments are carried out at two facilities. Experiments at low current (from several million to ten million Amperes) are conducted on the Pegasus II capacitor bank. Experiments with higher currents (10`s to 100`s MA range) are performed in Ancho Canyon with the explosively driven Procyon and MAGO magnetic flux compression generator systems. In this paper, the authors present a survey of diagnostic capabilities and results from several sets of experiments. First, they discuss the initiation and growth of instabilities in plasmas generated from the implosion of hollow z-pinches in the pegasus and Procyon experiments. Next they discuss spectroscopic data from the plasmas produced by the MAGO system. They also show time resolved imaging data from thick ({approximately} .4 mm) liner implosions. Finally, the authors discuss improvements to x-ray and visible light imaging and spectrographic diagnostic techniques. The emphasis of this paper is not so much a detailed discussion of the experiments, but a presentation of imaging and spectroscopic results and the implications of these observations to the experiments.
Date: September 1, 1996
Creator: Oona, H.; Anderson, B. & Benage, J.
Partner: UNT Libraries Government Documents Department

Properties of plasma radiation diagnostics

Description: A number of diagnostics utilizing the radiation emitted from high-temperature plasmas have been developed at Los Alamos. Photoemissive x-ray diodes with photon energy bandpass filters provide time resolved rough spectral data from bout 6 eV to > 10 keV photon energy. Filtered silicon photodiodes can be used down to 1 eV and offer the advantages of nominally flat response and ability to operate in poor vacuum conditions. Both types of diodes will provide a rough time resolved spectrum and both are relatively inexpensive, reliable, and passive (i.e. no synchronization problems). For higher energy resolution bent crystal spectrographs are used in the x-ray region. With the addition of streak cameras or gated microchannel plates these systems provide data with high energy and high time resolution. To measure the total energy output a thin foil bolometer is used that measures the change in foil resistance as it is heated by the plasma radiation. Information on the physical location of the plasma is provided by a suite of visible framing cameras and x-ray pinhole cameras. By combining these diagnostics into a complementary set good diagnostic information can be guaranteed on any plasma experiment.
Date: June 1, 1996
Creator: Idzorek, G.C. & Oona, H.
Partner: UNT Libraries Government Documents Department

Measurement of x-rays emitted from projectiles moving in solid targets

Description: The results of three separate experiments all dealing with the production of x-rays in projectiles moving in solids are discussed. The first experiment deals with the measurement of line widths of x-rays emitted from projectiles moving in solid targets. The effect of collisional broadening of x- rays is found to dominate the line widths giving greater than an order of magnitude increase in the measured line widths. The second experiment studies ''solid target effects'' in producing non-binomial distributions of characteristic K x-ray spectra in heavy ion-atom collisions. The third experiment studies aluminum K x-ray production in Ar$sup +$ $Yields$ Al collisions in very thin aluminum foils as a function of foil thickness. Parameterization of the observed non-linear dependence enables the lifetime of the argon 2p vacancy and total ionization cross sections for the argon L-shell in Ar $Yields$ Al collisions to be measured. (auth)
Date: January 1, 1975
Creator: Fortner, R.J.; Matthews, D.L.; Feldman, L.C.; Garcia, J.D. & Oona, H.
Partner: UNT Libraries Government Documents Department

Procyon high explosive pulsed power experiments

Description: Procyon is a two-stage explosive pulsed-power system, consisting of a MK-IX helical generator and an explosively formed fuse (EFF) opening switch. A complete assembly including load and diagnostics is shown. The system was originally developed for the purpose of powering plasma z-pinch experiments and, in its original concept, was coupled to the plasma z-pinch load through a third pulsed power stage, a plasma flow switch (PFS). The authors have performed plasma z-pinch experiments both with and without a PFS, and they have now conducted the first heavy liner experiment. In this paper, they will summarize the results obtained to date with the system, and briefly discuss future applications.
Date: September 1, 1996
Creator: Goforth, J.H.; Oona, H. & Anderson, B.G.
Partner: UNT Libraries Government Documents Department

Experiments on planar plasma flow switches at Los Alamos

Description: The authors have performed a series of experiments on the Colt facility at Los Alamos to study the performance of plasma flow switches and to understand the important physics issues which affect that performance. These experiments were done in planar geometry on a small machine to allow for better diagnostic access and a higher repetition rate. The Colt facility is a capacitor bank which stores 300 kJ at maximum charge and produced a peak current of 1.1 MA in 2.0 microseconds for these experiments. The diagnostics used for these experiments included an array of b-dot probes, visible framing pictures, visible spectroscopy, and laser interferometry. Characteristics of the switch are determined from spatial and temporal profiles of the magnetic field and the spatial profile and temperature of the switch plasma. Here the authors present results from experiments for a variety of switch conditions.
Date: December 1997
Creator: Benage, J. F., Jr.; Wysocki, F. J.; Bowers, R. & Oona, H.
Partner: UNT Libraries Government Documents Department

Isentropic compression of argon

Description: The compression was done in an MC-1 flux compression (explosive) generator, in order to study the transition from an insulator to a conductor. Since conductivity signals were observed in all the experiments (except when the probe is removed), both the Teflon and the argon are becoming conductive. The conductivity could not be determined (Teflon insulation properties unknown), but it could be bounded as being {sigma}=1/{rho}{le}8({Omega}cm){sub -1}, because when the Teflon breaks down, the dielectric constant is reduced. The Teflon insulator problem remains, and other ways to better insulate the probe or to measure the conductivity without a probe is being sought.
Date: June 1, 1997
Creator: Veeser, L.R.; Ekdahl, C.A. & Oona, H.
Partner: UNT Libraries Government Documents Department

Instabilities in foil implosions and the effect of radiation output

Description: One of the aims of the Athena program at the Los Alamos National Laboratory is the generation of a high fluence of soft x-rays from the thermalization of an radially imploding foil. In the experiments in Athena program, a large axial current is passed through a cylindrical aluminum foil. Under the action of the Lorentz force, the resulting plasma accelerates toward the axis, thermalizes, and produces a fast soft x-ray pulse with a blackbody temperature up to several hundred electron volts. In order that there be the maximum power compression and the highest x-ray fluence and temperature, the plasma stagnation on axis must occur very promptly. This requires that the imploding plasma be as thin and symmetric as possible. A serious problem in the thermalization process is the formation of instabilities in the plasma due to the self-magnetic field that governs the implosion of foil. A large diagnostic effort was developed to capture the details of the implosion and instability growth in several foil implosion experiments. In this report, we will present visible light images and x-ray data designed to study the effects of foil mass, current, and initial perturbations on the instability growth during foil implosion. Representative data is presented from several experiments using the Pegasus capacitor bank system and the explosively driven Procyon system. These experiments are labeled Peg 25 and Peg 33 for the Pegasus experiments and PDD1, PDD2 and PRF0 for the Procyon experiments. In these experiments, all foils had radii of 5 centimeters but varied in mass and initial conditions. Experimental data from several shots were compared with each other and to a radiation magnetohydrodynamic (RMHD) computation and described in a separate paper.
Date: August 1, 1995
Creator: Oona, H.; Peterson, D.L. & Goforth, J.H.
Partner: UNT Libraries Government Documents Department

Review of the Procyon explosive pulsed power system

Description: The Procyon explosive pulsed power system is designed for powering plasma z-pinch experiments. It begins with a helical explosive-driven magnetic flux compression generator (MCG) for amplifying seed current from a capacitor bank into a storage inductor. One conductor element of the storage inductor is an explosively formed fuse (EFF) opening switch tailored to divert current to a plasma flow switch (PFS) in less than 3 [mu]s. The PFS, in turn, delivers current to a z-pinch load. Experiments to date have concentrated on the explosive pulsed power components and PFS. This paper focuses on the results of a recent full energy MCG/EFF/PFS test.
Date: January 1, 1993
Creator: Goforth, J.H.; Oona, H. & Greene, A.E. (and others)
Partner: UNT Libraries Government Documents Department

Study of atomic physics and population inversions with plasma focus

Description: The plasma focus can be used to generate high temperature and high density plasmas. Neon-like plasmas have previously been studied in Z-pinches and laser produced plasmas as sources for XUV and x-ray lasers. The plasma focus provides a simple and inexpensive source for studying atomic physics of highly ionized atoms. A detailed understanding of atomic physics at high temperatures, densities, and megagauss magnetic fields is necessary for possible x-ray laser designs. Methods that are generally used for obtaining population inversions include collisional ionization of the inner shells of multi-electron atoms and ions, photoexcitation, and electron collisional excitation of ions, collisional combination of ions, and atom-ion resonant charge exchange. We will discuss some possible experiments to help understand the atomic physics under the above condition. Some ideas and calculations will be given to show the feasibility of doing atomic physics relating to x-ray lasers with a plasma focus. 13 refs., 2 figs.
Date: January 1, 1989
Creator: Oona, H.; Hodgdon, M.L.; Rickel, D.G. & Freeman, B.L.
Partner: UNT Libraries Government Documents Department

High power opening switches for flux compression generator applications: An overview

Description: The high performance explosively powered flux compression generator (FCG) represents a proven source of very large electrical energies, at very high currents, low impedances, and modest powers that is suitable for powering a variety of plasma and beam experiments. Flux compressors have the advantage of delivering energy at low and high current and are ideal for energizing inductive energy storages. They are straightforward, compact, and inexpensive, when evaluated on the basis of cost per joule for a limited number of experiments. Conventional flux compressors have the disadvantage of delivering these enormous energies on relatively long timescales thus making some form of power conditioning essential for powering many interesting loads. Since flux compressors are ideally suited to energizing inductive loads, power conditioning systems based upon inductive store/opening switch techniques are complementary to FCG energy sources. For some experiments, straightforward application of one of a variety of high-current interrupters can provide the needed power conditioning. For more demanding experiments, multi-stage combination of switches may be required. And for loads requiring voltages in excess of a few hundred kilovolts, opening switches coupled with energy storage transformers are suitable. In this paper, we will review switch concepts that have been used in conjunction with flux compressors which deliver energies in the range of 1--20 MJ. These concepts include conventional electrically-exploded fuses, explosively-formed fuses, plasma-dynamic switches, and combinations of these elements. 6 refs., 12 figs.
Date: January 1, 1989
Creator: Reinovsky, R.E.; Goforth, J.H.; Lindemuth, I.R. & Oona, H.
Partner: UNT Libraries Government Documents Department

Review of the Procyon Explosive Pulsed Power System

Description: The Procyon explosive pulsed power system is designed for powering plasma z-pinch experiments. It begins with a helical explosive-driven magnetic flux compression generator (MCG) for amplifying seed current from a capacitor bank into a storage inductor. One conductor element of the storage inductor is an explosively formed fuse (EFF) opening switch tailored to divert current to a plasma flow switch (PFS) in less than 3 {mu}s. The PFS, in turn, delivers current to a z-pinch load. Experiments to date have concentrated on the explosive pulsed power components and PFS. This paper focuses on the results of a recent full energy MCG/EFF/PFS test.
Date: July 1, 1993
Creator: Goforth, J. H.; Oona, H. & Greene, A. E.
Partner: UNT Libraries Government Documents Department

Foil implosion studies on PEGASUS

Description: PEGASUS is a 1.5 MJ capacitor bank facility used in the Los Alamos Trailmaster foil implosion program. The experiments on this facility are to serve as a diagnostic testbed and foil physics benchmark for foil implosions with explosive generators as drivers. During the first year of operation, foil implosions have been driven by discharging the bank directly into a very thin Aluminum 2500 /angstrom/ thick free-standing foil without any pulse sharpening techniques; so-called ''direct drive.''These direct drive experiments have served as initial tests to optimize bank performance and foil implosion experimental techniques. The results to date are presented below. 1 ref., 2 figs.
Date: January 1, 1989
Creator: Cochrane, J.C.; Bartsch, R.R.; Begay, F.; Kruse, H.W.; Oona, H.; Parker, J.V. et al.
Partner: UNT Libraries Government Documents Department

Applications of the computer codes FLUX2D and PHI3D for the electromagnetic analysis of compressed magnetic field generators and power flow channels

Description: We present herein the results of three electromagnetic field problems for compressed magnetic field generators and their associated power flow channels. The first problem is the computation of the transient magnetic field in a two-dimensional model of helical generator during loading. The second problem is the three-dimensional eddy current patterns in a section of an armature beneath a bifurcation point of a helical winding. Our third problem is the calculation of the three-dimensional electrostatic fields in a region known as the post-hole convolute in which a rod connects the inner and outer walls of a system of three concentric cylinders through a hole in the middle cylinder. While analytic solutions exist for many electromagnetic field problems in cases of special and ideal geometries, the solutions of these and similar problems for the proper analysis and design of compressed magnetic field generators and their related hardware require computer simulations. In earlier studies, computer models have been proposed, several based on research oriented hydrocodes to which uncoupled or partially coupled Maxwell's equations solvers are added. Although the hydrocode models address the problem of moving, deformable conductors, they are not useful for electromagnetic analysis, nor can they be considered design tools. For our studies, we take advantage of the commercial, electromagnetic computer-aided design software packages FLUX2D nd PHI3D that were developed for motor manufacturers and utilities industries. 4 refs., 6 figs.
Date: January 1, 1989
Creator: Hodgdon, M.L.; Oona, H.; Martinez, A.R.; Salon, S.; Wendling, P.; Krahenbuhl, L. et al.
Partner: UNT Libraries Government Documents Department

Ion source development for the Los Alamos heavy ion fusion injector

Description: A multi-beam injector is being designed and built at Los Alamos for the US Heavy Ion Fusion Program. As part of this program, development of an aluminum-spark, pulsed plasma source is being carried out. Faraday cup diagnostics are used to study current emission and to map the current profile. An aluminum oxide scintillator with photographic film is used in conjunction with a pepper-pot to obtain time integrated emittance values.
Date: January 1, 1985
Creator: Rutkowski, H.L.; Oona, H.; Meyer, E.A.; Shurter, R.P.; Engelhardt, L.S. & Humphries, S. Jr.
Partner: UNT Libraries Government Documents Department

Beam rotation and shear in a large electron beam diode

Description: The time averaged electron beam current distribution of one of the electron guns of the Large Aperture Module (LAM) of the Aurora laser was measured as part of a larger set of experiments designed to study the electron beam transport to and energy deposition in the LAM laser chamber. The LAM laser chamber has a 1-m {times} 1-m aperture and is pumped from two sides along a 2-m length. A 10 ga. stainless steel sheet was placed inside the laser chamber and served multiple purposes. First, it was used to convert high energy electrons into X-rays in order to make radiograms of the electron beam. Second, the sheet was used as a Faraday cup to measure the total beam current. Third, individual Faraday cups were mounted on the plate to sample the time history of the electron beam at various positions. Each of the LAM electron gun diodes produces a beam of 750 kV electrons with a total current of about 500 kA which is relatively uniform over the cathode area of 1 m {times} 2 m. An applied magnetic field of about 1300 Gauss is used to prevent pinch of the beam during beam transport.
Date: January 1, 1990
Creator: Mansfield, C.R.; Oona, H. & Shurter, R.P.
Partner: UNT Libraries Government Documents Department

Advances in explosively formed fuse opening switches

Description: The development of Explosively Formed Fuses along two separate lines is discussed. One design, which has previously been demonstrated to conduct a 9.5 MA 350 ..mu..s risetime pulse and interrupt it in 1.2 ..mu..s. This scaled up design should operate at up to 15 MA with 20 nH loads. A second design with enhanced performance characteristics is being examined and will be tested on a small scale. This design includes opening switch inductance as part of the inductive store and, as a result, should have shorter pulse transfer times and should be able to be scaled to handle currents up to approx. 25 MA with 20 nH loads.
Date: January 1, 1987
Creator: Goforth, J.H.; Caird, R.S.; Greene, A.E.; Lindemuth, I.R.; Marsh, S.P.; Oona, H. et al.
Partner: UNT Libraries Government Documents Department

Five to ten MA experiments using flat plate explosive generators

Description: High explosive pulsed power (HEPP) techniques can address a wide range of pulsed power needs. The basis for HEPP techniques is the use of high explosives to reduce the inductance of a current-carrying circuit, thus multiplying the current due to magnetic flux conservation. For the past twenty years at Los Alamos, our high energy density physics (HEDP) program has followed a path leading to more sophisticated and higher current (and often power) systems. Twenty years ago, we had the capability of conducting tests at 10, or even 30 MA, with no power conditioning and low inductance loads. The time scale of the experiment was the time it took to compress the flux explosively, and our fastest generator with high current capability was a plate generator. The operating time of the generator is less than 15 {micro}s, and flux loading requires either an additional {approx}60 {micro}s or a reduced-efficiency inductive coupling scheme. We could also deliver shortened pulses to select loads by completing our generator circuit, initially, with a relatively high inductance circuit element, then switching in a lower inductance with 2-3 {micro}s left of the generator pulse. Figure 1 shows the results of such a test. The test was conducted in 1974 to investigate our capability to drive plasma z-pinch experiments for the production of soft x-rays, and was a pulsed power success. However, our understanding of vacuum power flow issues was not mature enough at that time to design a functioning plasma z-pinch load. There was a renewed need for such a system in 1980, and at that time we began assembling a complete set of techniques required for success. We first fielded a baseline test using a simplified version of the HEPP system that generated the Figure 1 data. Subsequent tests followed a 'bite size' philosophy. That is, ...
Date: January 1, 2001
Creator: Caird, R. S.; Fowler, C. M.; King, J. C. (James Carrel); Oona, H. (Henn); Tasker, D. G. (Douglas G.) & Goforth, J. H. (James H.)
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

Photon burst mass spectrometry--ultrasensitive detection of rare isotopes

Description: Progress is reported on the development of a new technique for measurement of trace levels of radioisotopes which is based on fluorescence detection of output from a mass spectrometer. Significant achievements include the observation of fluorescence and burst signals from Kr isotopes, including enriched samples of {sup 85}Kr with a 4-collector system. An abundance sensitivity is demonstrated with {sup 83}Kr and {sup 85}Kr.
Date: February 1, 1995
Creator: Hansen, C.S.; Pan, X.J.; Fairbank, W.M. Jr.; Oona, H.; Chamberlin, E.P.; Nogar, N.S. et al.
Partner: UNT Libraries Government Documents Department

Isentropic Compression of Argon

Description: We are studying the transition of argon from an insulator to a conductor by compressing the frozen gas isentropically to pressures at which neighboring atomic orbitals overlap sufficiently to allow some electron motion between atoms. Argon and the other rare gases have closed electron shells and therefore remain montomic, even when they solidify. Their simple structure makes it likely that any measured change in conductivity is due to changes in the atomic structure, not in molecular configuration. As the crystal is compressed the band gap closes, allowing increased conductivity. We have begun research to determine the conductivity at high pressures, and it is our intention to determine the compression at which the crystal becomes a metal.
Date: August 1997
Creator: Oona, H.; Solem, J. C.; Veeser, L. R.; Ekdahl, C. A.; Rodriquez, P. J.; Younger, S. M. et al.
Partner: UNT Libraries Government Documents Department

Comparison and analysis of 2-D simulation results with two implosion radiation experiments on the Los Alamos Pegasus I and Pegasus II capacitor banks

Description: Two experiments, PegI-41, conducted on the Los Alamos Pegasus I capacitor bank, and PegII-25, on the Pegasus II bank, consisted of the implosions of 13 mg (nominal), 5 cm radius, 2 cm high thin cylindrical aluminum foils resulting in soft x-ray radiation pulses from the plasma thermalization on axis. The implosions were conducted in direct-drive (no intermediate switching) mode with peak currents of about 4 MA and 5 MA respectively, and implosion times of about 2.5 {micro}s and 2.0 {micro}s. A radiation yield of about 250 kJ was measured for PegII-25. The purpose of these experiments was to examine the physics of the implosion and relate this physics to the production of the radiation pulse and to provide detailed experimental data which could be compared with 2-D radiation-magnetohydrodynamic (RMHD) simulations. Included in the experimental diagnostic suites were faraday rotation and dB/dt current measurements, a visible framing camera, an x-ray stripline camera, time-dependent spectroscopy, bolometers and XRD`S. A comparison of the results from these experiments shows agreement with 2-D simulation results in the instability development, current, and radiation pulse data, including the pulsewidth, shape, peak power and total radiation yield as measured by bolometry. Instabilities dominate the behavior of the implosion and largely determine the properties of the resulting radiation pulse. The 2-D simulations can be seen to be an important tool in understanding the implosion physics.
Date: September 1, 1995
Creator: Peterson, D.L.; Bowers, R.L.; Lebeda, C.F.; Matuska, W.; Benage, J.; Idzorek, G. et al.
Partner: UNT Libraries Government Documents Department

Computational modeling of the Trailmaster Procyon system

Description: The goal of the Los Alamos Foil Implosion project (Trail-master) is the development of an intense source of soft x-rays for materials and fusion studies. The x-ray source in the Trailmaster project is a foil initiated z-pinch. The next system in the Trailmaster project is designed to deliver 15 MA of current to the imploding linear creating approximately 1 MJ of soft x-ray radiation in a submicrosecond pulse. This system, designated Procyon, will consist of a Mark 9 helical explosive generator, an explosively formed fuse (EFF) opening switch, detonator closing switches, a vacuum powerflow channel, a plasma flow switch (PFS), and the imploding foil load. In the present paper we will focus on the computational modeling of the overall Procyon system. This effort includes circuit and zero-dimensional point mass (slug) modeling, 1-D and 2-D radiation MHD calculations and 3-D radiation transport and view factor modeling of the vacuum powerflow channel. 7 refs., 10 figs.
Date: January 1, 1991
Creator: Greene, A.E.; Bowers, R.L.; Brownell, J.H.; Peterson, D.L.; Weiss, D.L.; Oona, H. et al.
Partner: UNT Libraries Government Documents Department

Performance of the LAGUNA pulsed power system

Description: The goal of the LAGUNA experimental series of the Los Alamos National Laboratory TRAILMASTER program is to accelerate an annular aluminum plasma z-pinch to greater than one hundred kilojoules of implosion kinetic energy. To accomplish this, an electrical pulse >5.5 MA must be delivered to a 20 nH load in approx.1 ..mu..s. The pulsed power system for these experiments consists of a capacitor bank for initial energy storage, a helical explosive-driven magnetic-flux compression generator for the prime power supply and opening and closing switches for power conditioning. While we have not yet achieved our design goal of 15 MA delivered to the inductive store of the system, all major components have functioned successfully at the 10 MA level. Significant successes and some difficulties experienced in these experiments are described.
Date: January 1, 1987
Creator: Goforth, J.H.; Caird, R.S.; Fowler, C.M.; Greene, A.E.; Kruse, H.W.; Lindemuth, I.R. et al.
Partner: UNT Libraries Government Documents Department