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Hypervelocity microparticle characterization

Description: To protect spacecraft from orbital debris requires a basic understanding of the processes involved in hypervelocity impacts and characterization of detectors to measure the space environment. Both require a source of well characterized hypervelocity particles. Electrostatic acceleration of charged microspheres provides such a source. Techniques refined at the Los Alamos National Laboratory provided information on hypervelocity impacts of particles of known mass and velocity ranging from 20-1000 nm diameter and 1-100 km/s. A Van De Graaff generator operating at 6 million volts was used to accelerate individual carbonyl iron microspheres produced by a specially designed particle source. Standard electrostatic lenses and steering were used to control the particles flight path. Charge sensitive pickoff tubes measured the particle charge and velocity in- flight without disturbing the particle. This information coupled with the measured Van De Graaff terminal voltage allowed calculation of the particle energy, mass, momenta and (using an assumed density) the size. Particles with the desired parameters were then electrostatically directed to a target chamber. Targets used in our experiments included cratering and foil puncture targets, microphone momentum enhancement detectors, triboluminescent detectors, and ``splash`` charge detectors. In addition the system has been used to rapidly characterize size distributions of conductive plastic particles and potentially provide a method of easily sorting microscopic particles by size.
Date: November 1, 1996
Creator: Idzorek, G.C.
Partner: UNT Libraries Government Documents Department

Analysis of filtered silicon diode data from the MAGO II and MAGO III experiments

Description: The magnetic compression (MAGO) experiments were conceived by the All-Russia Scientific Institute for Experimental Physics (VNIIEF) several years ago, and only recently has Los Alamos National Laboratory (LANL) participated in joint US/Russian experiments intended to combine the advanced US diagnostic technology with the unsurpassed explosive pulsed power technology fielded by VNIIEF. On two of the four joint LANL/VNIIEF magnetized plasma generation (MAGO) experiments fielded thus far, filtered silicon diode measurements of the plasma emission were made. Both VNIIEF and Los Alamos have analyzed the data from those two sets of measurements. Here the results of the Los Alamos analysis are given. In these experiments sets of filtered silicon diodes were used to measure the plasma soft X-ray emission integrated by the different band passes of the thin metal and plastic filters. The filtered silicon diode diagnostic on MAGO III represented a considerable advance over the same diagnostic fielded on MAGO II, but experimental details resulted in data that is very difficult to interpret in a quantitative way. An attempt to derive the spectral character from some of the MAGO III data that might be salvageable does not seem worthwhile. The codes and procedures developed for MAGO III have been valuable for interpreting MAGO II data, and should also be valuable for interpreting future filtered silicon diode data. Because of the better understanding of the physics processes associated with this diagnostic, and the reasonable agreement with the VNIIEF analysis for MAGO II the authors have more confidence in their ability to interpret the filtered silicon diode data from future MAGO experiments. They believe that the filtered silicon diode data from MAGO II is consistent with emission from a long-lived hot magnetized plasma, and that the temperature and density deduced from the data are reasonably consistent with the temperature and density computed ...
Date: September 1, 1996
Creator: Kirkpatrick, R.C. & Idzorek, G.
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

Silicon photodiode characterization from 1 eV to 10 keV

Description: Silicon photodiodes offer a number of advantages over conventional photocathode type soft x-ray detectors in pulsed power experiments. These include a nominally flat response, insensitivity to surface contamination, low voltage biasing requirements, sensitivity to low energy photons, excellent detector to detector response reproducibility, and ability to operate in poor vacuum or gas backfilled experiments. Silicon photodiodes available from International Radiation Detectors (IRD), Torrance, California have been characterized for absolute photon response from 1 eV to 10 keV photon energy, time response, and signal saturation levels. The authors have assembled individually filtered photodiodes into an array designated the XUV-7. The XUV-7 provides seven photodiodes in a vacuum leak tight, electrically isolated, low noise, high bandwidth, x-ray filtered assembly in a compact package with a 3.7 cm outside diameter. In addition they have assembled the diodes in other custom configurations as detectors for spectrometers. Their calibration measurements show factor of ten deviations from the silicon photodiode theoretical flat response due to diode sensitivity outside the center `sensitive area`. Detector response reproducibility between diodes appears to be better than 5%. Time response measurements show a 10-90% rise time of about 0.1 nanoseconds and a fall time of about 0.5 nanoseconds. Silicon photodiodes have proven to be a versatile and useful complement to the standard photocathode detectors for soft x-ray measurement and are very competitive with diamond for a number of applications.
Date: October 1, 1997
Creator: Idzorek, G.C. & Bartlett, R.J.
Partner: UNT Libraries Government Documents Department

Silicon photodiode soft x-ray detectors for pulsed power experiments

Description: Silicon photodiodes offer a number of advantages over conventional photocathode type soft x-ray detectors in pulsed power experiments. These include a nominally flat response, insensitivity to surface contamination, low voltage biasing requirements, sensitivity to low energy photons, excellent detector to detector response reproducibility, and ability to operate in poor vacuum or gas backfilled experiments. Silicon photodiodes available from International Radiation Detectors (IRD), Torrance, California have been characterized for absolute photon response from 1 eV to 10 keV photon energy, time response, and signal saturation levels. The authors calibration measurements show factor of ten deviations from the silicon photodiode theoretical flat response due to diode sensitivity outside the center `sensitive area`. Detector response reproducibility between diodes appears to be better than 5%. Time response measurements show a 10-90% rise time of about 0.1 nanoseconds and a fall time of about 0.5 nanoseconds.
Date: October 1, 1997
Creator: Idzorek, G.C. & Bartlett, R.J.
Partner: UNT Libraries Government Documents Department

Comparing calculated and measured x-ray images

Description: In recent years 2-dimensional radiation-magneto-hydrodynamic (RMHD) calculations have done quite well in matching some important observed parameters of a z-pinch implosion. As the authors gain experience, they field more complex experiments to compare with calculations. Here they discuss both time dependent and time integrated x-ray imaging on Pegasus. Images, using similar filters, are calculated and compared with the data. They also apply some image enhancement to the data.
Date: September 1, 1995
Creator: Matuska, W.; Benage, J.; Idzorek, G.; Lebeda, C. & Peterson, D.
Partner: UNT Libraries Government Documents Department

Soft x-ray diagnostics for pulsed power machines

Description: A variety of soft x-ray diagnostics are being fielded on the Los Alamos National Laboratory Pegasus and Procyon pulsed power systems and also being fielded on joint US/Russian magnetized target fusion experiments known as MAGO (Magnitoye Obzhatiye). The authors have designed a low-cost modular photoemissive detector designated the XRD-96 that uses commercial 1100 series aluminum for the photocathode. In addition to photocathode detectors a number of designs using solid state silicon photodiodes have been designed and fielded. They also present a soft x-ray time-integrated pinhole camera system that uses standard type TMAX-400 photographic film that obviates the need for expensive and no longer produced zero-overcoat soft x-ray emulsion film. In a typical experiment the desired spectral energy cuts, signal intensity levels, and desired field of view will determine diagnostic geometry and x-ray filters selected. The authors have developed several computer codes to assist in the diagnostic design process and data deconvolution. Examples of the diagnostic design process and data analysis for a typical pulsed power experiment are presented.
Date: August 1, 1995
Creator: Idzorek, G.C.; Coulter, W.L.; Walsh, P.J. & Montoya, R.R.
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

Progress with developing a target for magnetized target fusion

Description: Magnetized Target Fusion (MTF) is an approach to fusion where a preheated and magnetized plasma is adiabatically compressed to fusion conditions. Successful MTF requires a suitable initial target plasma with an embedded magnetic field of at least 5 T in a closed-field-line topology, a density of roughly 10{sup 18} cm{sup {minus}3}, a temperature of at least 50 eV, and must be free of impurities which would raise radiation losses. Target plasma generation experiments are underway at Los Alamos National Laboratory using the Colt facility; a 0.25 MJ, 2--3 {micro}s rise-time capacitor bank. The goal of these experiments is to demonstrate plasma conditions meeting the minimum requirements for a MTF initial target plasma. In the first experiments, a Z-pinch is produced in a 2 cm radius by 2 cm high conducting wall using a static gas-fill of hydrogen or deuterium gas in the range of 0.5 to 2 torr. Thus far, the diagnostics include an array of 12 B-dot probes, framing camera, gated OMA visible spectrometer, time-resolved monochrometer, filtered silicon photodiodes, neutron yield, and plasma-density interferometer. These diagnostics show that a plasma is produced in the containment region that lasts roughly 10 to 20 {micro}s with a maximum plasma density exceeding 10{sup 18} cm{sup {minus}3}. The experimental design and data are presented.
Date: September 1, 1997
Creator: Wysocki, F. J.; Chrien, R. E.; Idzorek, G.; Oona, H.; Whiteson, D. O.; Kirkpatrick, R. C. et al.
Partner: UNT Libraries Government Documents Department

On size scaling in shock hydrodynamics and the stress-strain behavior of copper at exceedingly high strain rates

Description: In recent years the Hypervelocity Microparticle Impact (HMI) project at Los Alamos has utilized electrostatically accelerated iron spheres of microscopic dimensions to generate hypervelocity impact experiments to about 100 {times} 10{sup 5} cm/sec, about an order of magnitude beyond the data range for precisely controlled impact tests with ordinary macroscopic particles. But the extreme smallness of the micro impact events brings into question whether the usual shock-hydrodynamic size scaling can be assumed. It is to this question of the validity of size scaling (and its refinement) that the present study is directed. Hypervelocity impact craters are compared in which the two impact events are essentially identical except that the projectile masses and crater volumes differ by nearly 12 orders of magnitude -- linear dimensions and times differing by 4 orders of magnitude. Strain rates at corresponding points increase 4 orders of magnitude in the size reduction. Departures from exact scaling, by a factor of 3.7 in crater volume, are observed for copper targets -- with the micro craters being smaller than scaling would predict. This is attributed to a factor 4.7 higher effective yield stress occurring in the micro cratering flow. This, in turn, is because the strain rate there is about 10{sup 8}/sec as compared to a strain rate of only 10{sup 4}/sec in the macro impact. The measurement of impact craters for very small impact events leads to the determination of metal yield stresses as strain rates more than two orders of magnitude greater than have been obtained by other methods. The determination of material strengths at these exceedingly high strain rates is of obvious fundamental importance. 10 refs., 4 figs.
Date: January 1, 1991
Creator: Walsh, J.M.; Stradling, G.L.; Idzorek, G.C.; Shafer, B.P. (Los Alamos National Lab., NM (United States)) & Curling, H.L. Jr. (Science Applications International Corp., Albuquerque, NM (United States))
Partner: UNT Libraries Government Documents Department

Soft X-Ray Measurements of Z-Pinch-Driven Vacuum Hohlraums

Description: This article reports the experimental characterization of a z-pinch driven-vacuum hohlraum. The authors have measured soft x-ray fluxes of 5 x 10{sup 12} W/cm{sup 2} radiating from the walls of hohlraums which are 2.4--2.5 cm in diameter by 1 cm tall. The x-ray source used to drive these hohlraums was a z-pinch consisting of a 300 wire tungsten array driven by a 2 MA, 100 ns current pulse. In this hohlraum geometry, the z-pinch x-ray source can produce energies in excess of 800 kJ and powers in excess of 100 TW to drive these hohlraums. The x-rays released in these hohlraums represent greater than a factor of 25 in energy and more than a factor of three in x-ray power over previous laboratory-driven hohlraums.
Date: July 21, 1999
Creator: Baker, K. L.; Porter, J. L.; Ruggles, L. E.; Chandler, G. A.; Deeney, Chris; Vargas, M. et al.
Partner: UNT Libraries Government Documents Department