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S C Bott,
G Collins,
K Gunasekera,
D Mariscal,
F N Beg,
D M Haas,
F Veloso,
I C Blesener,
A D Cahill,
C L Hoyt,
B R Kusse, D A Hammer
[show abstract]
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ABSTRACT: In this work we demonstrate a design for obtaining laser backlighting (e.g., interferometry) and time-resolved extreme ultraviolet self-emission images along the same line-of-sight. This is achieved by modifying a single optical component in the laser collection optics with apertures and pinhole arrangements suitable for single or multiple frame imaging onto a gated detector, such as a microchannel plate. Test results for exploding wire experiments show that machining of the optic does not affect the overall quality of the recovered laser images, and that, even with a multiple frame system, the area sacrificed to achieve collinear imaging is relatively small. The diagnostics can therefore allow direct correlation of laser and self-emission images and their derived quantities, such as electron density in the case of interferometry. Simple methods of image correlation are also demonstrated.
The Review of scientific instruments 08/2012; 83(8):083507. · 1.52 Impact Factor
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ABSTRACT: We report here the calibration and analysis techniques used to obtain spatially resolved density and temperature measurements of a pair of imploding aluminum wires from x-ray absorption spectra. A step wedge is used to measure backlighter fluence at the film, allowing transmission through the sample to be measured with an accuracy of ±14% or better. A genetic algorithm is used to search the allowed plasma parameter space and fit synthetic spectra with 20 μm spatial resolution to the measured spectra, taking into account that the object plasma nonuniformity must be physically reasonable. The inferred plasma conditions must be allowed to vary along the absorption path in order to obtain a fit to the spectral data. The temperature is estimated to be accurate to within ±25% and the density to within a factor of two. This information is used to construct two-dimensional maps of the density and temperature of the object plasma.
The Review of scientific instruments 07/2012; 83(7):073502. · 1.52 Impact Factor
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G. A. Mesyats,
T. A. Shelkovenko,
G. V. Ivanenkov,
A. V. Agafonov,
S. Yu. Savinov,
S. A. Pikuz,
I. N. Tilikin,
S. I. Tkachenko,
S. A. Chaikovskii,
N. A. Ratakhin,
V. F. Fedushchak,
V. I. Oreshkin,
A. V. Fedyunin,
A. G. Russkikh,
N. A. Labetskaya,
A. P. Artemov, D. A. Hammer,
D. B. Sinars
[show abstract]
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ABSTRACT: For the first time, the regime of a micrometer-size hot spot formation is impemented for an X-pinch in a plasma, which is
fed from a current generator based on low-inductance capacitors and rapid current switches. The configurations of X-pinches,
which can be used effectively as point sources of soft X-rays with this type of current generator, are determined. A prototype
of a small-size radiation source for high-resolution point projection X-ray radiography has been constructed. The main parameters
of X-pinch as a radiation source are analyzed and compared with X-pinch parameters in high-voltage setups with shaping lines.
An analysis of the data on the operation of X-pinches in generators with different parameters has led to simple relations
that can be used to select optimal initial X-pinch parameters.
Journal of Experimental and Theoretical Physics 04/2012; 111(3):363-370. · 1.03 Impact Factor
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[show abstract]
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ABSTRACT: Raising the power of X-ray emission from an X-pinch by increasing the pinch current to the megampere level requires the corresponding
increase in the initial linear mass of the load. This can be achieved by increasing either the number of wires or their diameter.
In both cases, special measures should be undertaken to prevent the formation of a complicated configuration with an uncontrolled
spatial structure in the region of wire crossing, because such a structure breaks the symmetry of the neck formed in the crossing
region, destabilizes plasma formation, and degrades X-ray generation. To improve the symmetry of the wire crossing region,
X-pinch configurations with a regular multilayer arrangement of wires in this region were proposed and implemented. The results
of experiments with various symmetric X-pinch configurations on the COBRA facility at currents of ∼1MA are presented. It is
shown that an X-pinch with a symmetric crossing region consisting of several layers of wires made of different materials can
be successfully used in megampere facilities. The most efficient combinations of wires in symmetric multilayer X-pinches are
found in which only one hot spot forms and that are characterized by a high and stable soft X-ray yield.
Plasma Physics Reports 04/2012; 36(1):50-66. · 0.65 Impact Factor
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Physics of Plasmas 02/2012; 19. · 2.15 Impact Factor
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Physics of Plasmas 02/2012; 19:022701. · 2.15 Impact Factor
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[show abstract]
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ABSTRACT: We present here the use of absorption spectroscopy of the continuum radiation from x-pinch-produced point x-ray sources as a diagnostic to investigate the properties of aluminum plasmas created by pulsed power machines. This technique is being developed to determine the charge state, temperature, and density as a function of time and space under conditions that are inaccessible to x-ray emission spectroscopic diagnostics. The apparatus and its characterization are described, and the spectrometer dispersion, magnification, and resolution are calculated and compared with experimental results. Spectral resolution of about 5000 and spatial resolution of about 20 μm are demonstrated. This spectral resolution is the highest available to date in an absorption experiment. The beneficial properties of the x-pinch x-ray source as the backlighter for this diagnostic are the small source size (<5 μm), smooth continuum radiation, and short pulse duration (<0.1 ns). Results from a closely spaced (1 mm) exploding wire pair are shown and the general features are discussed.
The Review of scientific instruments 06/2011; 82(6):063501. · 1.52 Impact Factor
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[show abstract]
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ABSTRACT: Radial foil configurations prove to be a very simple experimental setup to study high-energy-density plasmas. A thin metallic foil lies flat over a stretcher which is connected to the anode of a pulsed-power generator. The cathode contacts the foil at its geometrical center using a hollow stainless steel pin. Force densities should increase dramatically as the pin diameter diminishes, and we expect plasma properties to change accordingly. Based only on pin diameter considerations, radial foil explosions at 1 MA could produce magnetic pressures ranging from 160 kbar (for 2-mm pins) to 2.5 Mbar (for 0.5-mm pins). However, magnetohydrodynamic instabilities limit plasma performances. For large-diameter pins (2 mm), the force density is low, but the plasma is stable until the discharge current reaches 1.1 MA. For a smaller diameter (0.5 mm), instabilities appear when the discharge is 600 kA before the current peaks. While an increase in the local plasma electron density and temperature is noticeable as the cathode size diminishes, instabilities do limit overall plasma properties and require stabilization to obtain higher pressures.
IEEE Transactions on Plasma Science 01/2011; · 1.17 Impact Factor
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[show abstract]
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ABSTRACT: A hybrid X-pinch configuration consisting of solid conical electrodes connected by a wire has been tested on a 45 ns risetime, 500 kA peak current pulsed power generator. Wires of different materials were loaded through holes in the cones; wire lengths were varied from 0.6 to 2 mm. Most of these hybrid X-pinches generated an intense single burst of soft x-rays and developed a single hot spot that was of micron-scale size. Hybrid X-pinches generate less hard x-ray intensity than standard X-pinches.
Physics of Plasmas 11/2010; 17(11):112707-112707-5. · 2.15 Impact Factor
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[show abstract]
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ABSTRACT: Monochromatic x-ray backlighting has been employed with great success for imaging of plasmas with strong self-emission such as x-pinches and wire array z-pinches. However, implementation of a monochromatic backlighting system typically requires extremely high quality spherically bent crystals which are difficult to manufacture and can be prohibitively expensive. Furthermore, the crystal must have a direct line of sight to the object, which typically emits copious amounts of radiation and debris. We present a quasimonochromatic x-ray backlighting system which employs an elliptically bent mica crystal as the dispersive element. In this scheme a narrow band of continuum radiation is selected for imaging, instead of line radiation in the case of monochromatic imaging. The flat piece of mica is bent using a simple four-point bending apparatus that allows the curvature of the crystal to be adjusted in situ for imaging in the desired wavelength band. This system has the advantage that it is very cost effective, has a large aperture, and is extremely flexible. The principles of operation of the system are discussed and its performance is analyzed.
The Review of scientific instruments 10/2010; 81(10):10E501. · 1.52 Impact Factor
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ABSTRACT: High energy density (HED) plasmas, produced by diverse techniques, such as lasers or pulsed power generators, can help scientists to better understand extreme states of matter as well as astrophysical phenomena. While fast Z-pinches are the most common approach to generating HED plasmas in the pulsed power community, radial foil configurations can yield plasma pressures on the order of 0.5 Mbar on a 1 MA, 100 ns current rise time generator, similar to wire array configurations producing Z-pinches. In this experimental setup, a thin metallic foil stretched onto a circular anode connects to a very small 'pin' cathode at the center. Radial currents flow in the foil then down the pin cathode, thereby generating an axi-symmetric toroidal magnetic field under the foil. Initial experimental results (Gourdain et al 2010 Phys. Plasmas 17 012706) showed that the foil current interacts with this field and the resulting J × B force lifts the foil upward. Very rapidly the foil plasma turns into a bubble-shaped cavity above the central pin, and that bubble expands at 300 km s−1, until instabilities destroy the axial symmetry, bursting the bubble open. This paper complements these initial results by using time-integrated x-ray pin-hole cameras and a focusing spectrometer with spatial resolution. In addition to laser interferometry, these new data help to provide a better estimate of the plasma electron density inside the bubble, above 1020 cm−3, and of the electron temperature, between 300 and 400 eV inside the central plasma column. We also discovered the presence of 'bright' spots in the plasma, with densities larger than 5 × 1021 electrons cm−3 and temperatures above 1 keV. Finally laser interferometry gives a precise mapping of the initial plasma jet and bubble areal densities.
Plasma Physics and Controlled Fusion 04/2010; 52(5):055015. · 2.42 Impact Factor
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ABSTRACT: The growth of the axial instability in low wire number wire array Z pinches using a 100 ns rise time, 1 MA pulsed power accelerator is examined. The axial instability manifests itself as a quasiperiodic variation of the radius of the coronal plasma along each wire and a consequent modulation of the rate of ablation of material from the dense wire core. The dominant wavelength of the modulation becomes constant late in time. In this work laser shadowgraphy is used to measure the growth of the wavelength and amplitude of the instability as well as the size of the coronal plasma in aluminum wire arrays from the time of plasma formation to the time the wavelength seen late in time is reached. Using magnetic probes, the distribution of current and magnetic topology are also investigated. It is found that a distinct change in magnetic field topology associated with the onset of advection of current to the array axis by the streaming wire-ablation plasma appears to be responsible for ending the growth of the axial instability and initiating the quasisteady state ablation phase of the wire array Z pinch.
Physics of Plasmas 01/2010; 17(1):012704-012704-11. · 2.15 Impact Factor
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Physics of Plasmas 01/2010; 17(11). · 2.15 Impact Factor
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[show abstract]
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ABSTRACT: For the first time, a geometry has been developed to allow for an axial imaging system for wire-array Z-pinch experiments that produce high-resolution x-ray images. The new geometry required a significant redesign of the electrode hardware. Calibrated areal density measurements of the Z-pinch plasma including wire cores, coronal plasma, streaming plasma, and the precursor were obtained. The system used eight-wire molybdenum (Mo) X pinches in series with and directly below the Z-pinch axis to provide micron-scale x-rays sources for point-projection radiography. The images formed on the x-ray sensitive film had a 15 mm diameter field of view at the center height of the array and a magnification of about 7.5:1. Titanium (Ti) filters in front of the film transmitted radiation in the spectral range of 3-5 keV. For calibration, a separate film with the same thickness Ti filter was placed the same distance from the X pinch. This film had an unobstructed path that bypasses the Z-pinch but included step wedges for calibration of the Z-pinch plasma. The step wedges had thicknesses of tungsten (W) ranging from 0.015 to 1.1 microm to obtain areal density measurements of the W plasma from the wire-array. Images had subnanosecond temporal resolution and about 10 microm spatial resolution.
The Review of scientific instruments 12/2009; 80(12):123505. · 1.52 Impact Factor
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J. C. Zier,
J. D. Douglass,
I. C. Blesener,
K. S. Blesener,
D. A. Chalenski,
R. M. Gilgenbach,
J. B. Greenly, D. A. Hammer,
P. F. Knapp,
B. R. Kusse,
Y. Y. Lau,
R. D. McBride,
W. Syed,
E. P. Yu
[show abstract]
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ABSTRACT: Azimuthally correlated wire core ablation was compared for closely spaced versus widely spaced wires in a 1 MA Z-pinch. X-ray point-projection diagnostics revealed that 240 μm spaced wires exhibited a correlation coefficient approaching unity in both real space and in k-space. This correlated ablation between wires at a fixed axial location is believed to occur due to an enhanced, localized Joule heating. Wires separated by 2.47 mm or greater were uncorrelated in real space, but correlated in k-space, indicating the ablation structure between wires was shifted in phase.
Physics of Plasmas 10/2009; 16(10):102702-102702-6. · 2.15 Impact Factor
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S. C. Bott,
D. M. Haas,
Y. Eshaq,
U. Ueda,
F. N. Beg, D. A. Hammer,
B. Kusse,
J. Greenly,
T. A. Shelkovenko,
S. A. Pikuz, [......],
S. V. Lebedev,
S. N. Bland,
G. N. Hall,
F. A. Suzuki Vidal,
A. Marocchino,
A. Harvey-Thomson,
M. G. Haines,
J. B. A. Palmer,
A. Esaulov,
D. J. Ampleford
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ABSTRACT: The limited understanding of the mechanisms driving the mass ablation rate of cylindrical wires arrays is presently one of the major limitations in predicting array performance at the higher current levels required for inertial confinement fusion (ICF) ignition. Continued investigation of this phenomenon is crucial to realize the considerable potential for wire arrays to drive both ICF and inertial fusion energy, by enabling a predictive capability in computational modeling. We present the first study to directly compare the mass ablation rates of wire arrays as a function of the current rise rate. Formation of the precursor column is investigated on both the MAPGIE (1 MA, 250ns [
Mitchell et al., Rev. Sci. Instrum. 67, 1533 (1996)
]) and COBRA (1 MA, 100ns [
Greenly et al., Rev. Sci. Instrum. 79, 073501 (2008)
]) generators, and results are used to infer the change in the effective ablation velocity induced by the rise rate of the drive current. Laser shadowography, gated extreme ultraviolet (XUV) imaging, and x-ray diodes are used to compare the dynamical behavior on the two generators, and X-pinch radiography and XUV spectroscopy provide density evolution and temperature measurements respectively. Results are compared to predictions from an analytical scaling model developed previously from MAGPIE data, based on a fixed ablation velocity. For COBRA the column formation time occurs at 116±5 ns and for Al arrays and 146±5 ns for W arrays, with Al column temperature in the range of 70–165 eV. These values lie close to model predictions, inferring only a small change in the ablation velocity is induced by the factor of 2.5 change in current rise time. Estimations suggest the effective ablation velocities for MAGPIE and COBRA experiments vary by a maximum of 30%.
Physics of Plasmas 06/2009; 16(7):072701-072701-14. · 2.15 Impact Factor
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ABSTRACT: A symmetric X pinch configuration that is conducive to using large numbers of wires on ≥ 1 MA pulsed power generators has been tested at 1 MA. Using an initial configuration of wires before their twisting, similar to nested cylindrical wire arrays, enables a geometrically simple, compact, multilayer wire configuration at the X pinch crossing region. Multilayer X pinches with the same or different materials in the inner and outer wire layers were tested. Optimization resulted in X pinch radiation sources with peak power comparable to the most successful single layer X pinch, but with a compact, single bright X radiation source more reliably obtained using the nested configuration.
Physics of Plasmas 05/2009; 16(5):050702-050702-4. · 2.15 Impact Factor
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K. M. Williamson,
V. L. Kantsyrev,
A. A. Esaulov,
A. S. Safronova,
N. D. Ouart,
F. M. Yilmaz,
I. K. Shrestha,
V. Shlyaptseva,
R. D. McBride,
D. A. Chalenski,
J. D. Douglass,
J. B. Greenly, D. A. Hammer,
B. R. Kusse
[show abstract]
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ABSTRACT: The results of experiments with combined aluminum (Al) and stainless steel (SS) alloy 304, nested wire arrays from the 1 MA COBRA generator at Cornell University are presented. The loads studied consisted of a 6 mm diameter inner array and a 13 mm diameter outer array with a different material in each array: SS or aluminum. Al implodes before SS in all loads studied, even when Al was on the inner array. The new wire ablation dynamic model and spectroscopic modeling are used to interpret these data. The observed implosion dynamics are likely a result of the higher ablation rate of Al. These initial results suggest that combining wire materials with different ablation rates in wire array loads could be developed into a useful technique for x-ray pulse shaping and radiation yield optimization.
Physics of Plasmas 01/2009; 16(1):012704-012704-9. · 2.15 Impact Factor
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N. D. Ouart,
M. F. Yilmaz,
A. S. Safronova,
V. L. Kantsyrev,
A. A. Esaulov,
K. M. Williamson,
G. C. Osborne,
I. Shrestha,
M. E. Weller,
R. D. McBride,
P. F. Knapp,
K. S. Bell,
S. A. Pikuz,
T. A. Shelkovenko,
J. B. Greenly, D. A. Hammer,
B. R. Kusse
[show abstract]
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ABSTRACT: Implosions from compact cylindrical wire arrays (CCWA) with mid-Z and low-Z wires were carried out on the 1-MA COBRA generator at Cornell University. In particular, the CCWA used either Brass 310 (70% Cu, 30% Zn) wires or a combination of Brass 310 and Al 5056 (95% Al, 5% Mg) wires arranged in an alternating pattern. A total of 16 wires were used on either a 6 or 4 mm diameter array. The diagnostic suite included a bolometer, fast x-ray detectors, a time-integrated spectrometer, and a streak camera. A higher energy output was observed from bolometer measurements when alternating the brass and Al wires compared to using only the brass wires. This study will focus mainly on the spectroscopy of the brass and alternating brass and Al CCWA by applying the non-LTE kinetic models of Cu and Zn to account for the L-shell radiation. The resulting plasma parameters, electron density and electron temperature, will be discussed and compared for the CCWA with only brass wires and alternating brass and Al wires. The simulations with the novel Wire Ablation Dynamics Model that account for wire ablation will be performed to analyze the differences in implosion dynamics of the uniform and alternating compact cylindrical arrays.
AIP Conference Proceedings 01/2009; 1088(1).
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ABSTRACT: Some issues concerning high-current electron beam transport from the X pinch cross point to the diagnostic system and measurements of the beam current by Faraday cups are discussed. Results of computer simulation of electron beam propagation from the pinch to the Faraday cup give limits for the measured current for beams having different energy spreads. The beam is partially neutralized as it propagates from the X pinch to a diagnostic system, but within a Faraday cup diagnostic, space charge effects can be very important. Experimental results show evidence of such effects.
Review of Scientific Instruments 11/2008; · 1.37 Impact Factor
