-
D B Sinars,
R D McBride,
S A Pikuz,
T A Shelkovenko,
D F Wenger,
M E Cuneo,
E P Yu,
J P Chittenden,
E C Harding,
S B Hansen,
B P Peyton, D J Ampleford,
C A Jennings
[show abstract]
[hide abstract]
ABSTRACT: Using solid, machined X-pinch targets driven by currents rising from 0 to 5-6 MA in 60 ns, we observed bright spots of 5-9-keV continuum radiation from 5±2-μm diameter regions. The >6-keV radiation is emitted in about 0.4 ns, and the bright spots are roughly 75 times brighter than the bright spots measured at 1 MA. A total x-ray power of 10 TW peak and yields of 165±20 kJ were emitted from a 3-mm height. The 3-5-keV continuum radiation had a 50-90-GW peak power and 0.15-0.35-kJ yield. The continuum is plausibly from a 1275±75-eV blackbody or alternatively from a 3500±500-eV bremsstrahlung source.
Physical Review Letters 10/2012; 109(15):155002. · 7.37 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: For gas puff Z-pinches, the K-shell x-ray yield is maximized with the use of a multi-shell nozzle. Optimization of the yield, verification of hydrodynamic models of the nozzle flows, and plausible MHD code modeling of the implosions require data on the radial and axial (R,Z) distribution of mass in the nozzle's flow field. Interferometry is a well-established technique for acquiring such data. We describe the development and use of a two-dimensional interferometer with emphasis on the required data reduction methods. We also show that the instrument can derive the flow from each individual nozzle in a multi-shell system.
The Review of scientific instruments 08/2012; 83(8):083116. · 1.52 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Magnetic implosions provide extremely intense soft X-ray radiation on the Z accelerator. Shock heating at stagnation provides temperatures that are capable of producing K-shell radiation from stainless steel plasma. Time-gated multicolor X-ray pinhole imaging is used to study stagnation and disruption in fast Z pinches. Magnetohydrodynamic instabilities are observed to grow, following peak X-ray power until the Z-pinch column disrupts well after the main power pulse.
IEEE Transactions on Plasma Science 12/2011; · 1.17 Impact Factor
-
B Jones,
C A Jennings,
J E Bailey,
G A Rochau,
Y Maron,
C A Coverdale,
E P Yu,
S B Hansen, D J Ampleford,
P W Lake,
G Dunham,
M E Cuneo,
C Deeney,
D V Fisher,
V I Fisher,
V Bernshtam,
A Starobinets,
L Weingarten
[show abstract]
[hide abstract]
ABSTRACT: The observation of Doppler splitting in K-shell x-ray lines emitted from optically thin dopants is used to infer implosion velocities of up to 70 cm/μs in wire-array and gas-puff Z pinches at drive currents of 15-20 MA. These data can benchmark numerical implosion models, which produce reasonable agreement with the measured velocity in the emitting region. Doppler splitting is obscured in lines with strong opacity, but red-shifted absorption produced by the cooler halo of material backlit by the hot core assembling on axis can be used to diagnose velocity in the trailing mass.
Physical Review E 11/2011; 84(5 Pt 2):056408. · 2.26 Impact Factor
-
D B Sinars,
D F Wenger,
S A Pikuz,
B Jones,
M Geissel,
S B Hansen,
C A Coverdale, D J Ampleford,
M E Cuneo,
L A McPherson,
G A Rochau
[show abstract]
[hide abstract]
ABSTRACT: We describe a pair of time-integrated transmission spectrometers that are designed to survey 7-28 keV (1.9 to 0.43 Å) x-ray photons produced by experiments on the Sandia Z pulsed power facility. Each spectrometer uses a quartz 10-11 crystal in a Cauchois geometry with a slit to provide spatial resolution along one dimension. The spectrometers are located in the harsh environment of the Z vacuum chamber, which necessitates that their design be compact and rugged. Example data from calibration tests and Z experiments are shown that illustrate the utility of the instruments.
The Review of scientific instruments 06/2011; 82(6):063113. · 1.52 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Wire array z-pinches have been used successfully for many years as a powerful x-ray source, as a dynamic hohlraum, and as an intense K-shell radiation source. Significant progress has been made in the effective modeling of these three-dimensional (3D) resistive plasmas. However, successful modeling also requires an accurate representation of the power delivered to these loads from the generator, which is an uncertainty potentially as large as the magnetohydrodynamic (MHD) implosion dynamics. We present 3D resistive MHD simulations of wire arrays that are coupled to transmission line equivalent models of the Z generator, driven by voltage sources derived directly from electrical measurements. Significant (multi-mega-ampère) current losses are shown to occur in both the convolute and the final feed. This limits the array performance and must be correctly accounted for to accurately represent the generator response to the load. Our simulations are validated against data for compact: 20 mm diameter, 10 mm long wire arrays that have produced the highest x-ray power densities on Z. This is one of the most comprehensive experimental data sets for single and nested wire arrays and includes voltage, current, x-ray power and energy, and multiple mass distribution measurements. These data tightly constrain our simulation results and allow us to describe in detail both the implosion and stagnation, and how energy is delivered to, and radiated from z-pinch loads. We show that the radiated power is consistent with the kinetic energy delivered to a distributed 3D mass profile over its implosion and stagnation. We also demonstrate how the local inductance of the transmission line connecting to the wire array is responsible for delivering more than 50% of the total radiated power. This makes the power output dependent on the design of specific elements of the generator, and their response to the imploding load, and not just on the peak current that can be delivered.
Physics of Plasmas 09/2010; 17(9):092703-092703-16. · 2.15 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We have used a collisional-radiative spectroscopic model to generate a stainless steel (SS) atomic model to analyze the implosion dynamics of an array of SS wires on the Z and/or refurbished Z accelerator at the U.S. Sandia National Laboratories. This approach combines the completeness of highly averaged Rydberg state models with the accuracy of detailed models for all important excited states. Our atomic model includes a very large number of levels and atomic structure data, as well as excitation, ionization, and recombination level coupling. We have investigated the ionization dynamics and generated K- and L-shell spectra using the conditions in the Z accelerator, as calculated by a 1-D nonlocal thermodynamic equilibrium (LTE) radiation hydrodynamics model. This investigation using more detailed and accurate atomic models supersedes earlier spectroscopic simulation of K-shell SS spectra to analyze spectra on the Z accelerator. The non-LTE populations are obtained by generating the detailed atomic data for Fe, Ni, and Cr, and Mn ions, the constituents of SS. Analysis of our spectra using self-consistently generated data from the flexible atomic code shows excellent agreement with experimental data of shots Z581 and Z1860. We have also included level-specific dielectronic recombination from H- to He-like ions and inner-shell excitation rates from excited states of He-like ions in our atomic model and investigated the Ly<sub>??</sub> satellite lines that are useful for diagnosing Doppler broadening in a Z -pinch plasma at stagnation.
IEEE Transactions on Plasma Science 05/2010; · 1.17 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: Compact tungsten wire array Z -pinches imploded on the Z generator at Sandia National Laboratories have proven to be a powerful reproducible X-ray source. Wire arrays have also been used in dynamic hohlraum radiation flow experiments and as an intense K-shell source, while the generator has been used extensively for isentropic compression experiments. A problem shared by all these applications is current loss, preventing the ~20-MA drive current from being reliably coupled to the load. This potentially degrades performance, while uncertainties in how this loss is described limit our predictive capability. We present details of a transmission line equivalent circuit model of the Z generator for use in driving 3-D resistive MHD simulations of wire array loads. We describe how power delivery to these loads is affected by multiple current losses and demonstrate how these may be calculated or reconstructed from available electrical data for inclusion in the circuit model. We then demonstrate how the circuit model and MHD load calculation may be combined to infer an additional current loss that has not been directly diagnosed for wire arrays.
IEEE Transactions on Plasma Science 05/2010; · 1.17 Impact Factor
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B Jones, D J Ampleford,
R A Vesey,
M E Cuneo,
C A Coverdale,
E M Waisman,
M C Jones,
W E Fowler,
W A Stygar,
J D Serrano,
M P Vigil,
A A Esaulov,
V L Kantsyrev,
A S Safronova,
K M Williamson,
A S Chuvatin,
L I Rudakov
[show abstract]
[hide abstract]
ABSTRACT: An indirect drive configuration is proposed wherein multiple compact Z-pinch x-ray sources surround a secondary hohlraum. Planar compact wire arrays allow reduced primary hohlraum surface area compared to cylindrical loads. Implosions of planar arrays are studied at up to 15 TW x-ray power on Saturn with radiated yields exceeding the calculated kinetic energy, suggesting other heating paths. X-ray power and yield scaling studied from 1-6 MA motivates viewfactor modeling of four 6-MA planar arrays producing 90 eV radiation temperature in a secondary hohlraum.
Physical Review Letters 03/2010; 104(12):125001. · 7.37 Impact Factor
-
D.V. Rose,
D.R. Welch,
R.E. Clark,
E.A. Madrid,
C.L. Miller,
C. Mostrom,
W.A. Stygar,
M.E. Cuneo,
C.A. Jennings,
B. Jones, D.J. Ampleford,
K.W. Struve
[show abstract]
[hide abstract]
ABSTRACT: Post-hole convolutes are used in high-power transmission line systems and join several individual transmission lines in parallel, transferring the combined currents to a single transmission line attached to a load. Magnetic insulation of electron flow, established upstream of the convolute region, is lost at the convolute due, in part, to the formation of magnetic nulls, resulting in current losses. At very high-power operating levels, the formation of electrode plasmas is considered likely which can lead to additional losses. A recent computational analysis of the Sandia Z accelerator suggested that modest plasma desorption rates in the convolute region could explain measured current losses. The recently completed Sandia ZR accelerator has utilized new convolute designs to accommodate changes to the parallel-plate transmission lines on ZR. Detailed particle-in-cell simulations that are fully electromagnetic and relativistic, and include plasma desorption from electrode surfaces in the post-hole convolutes, are carried out to assess the measured current losses on ZR. We find that the plasma desorption rate used to model the Z convolute also applies to three different ZR convolute designs that have been fielded. Based on these findings, the simulation model is being used to develop newer convolute designs with the goal of reducing the current losses, particularly for higher-impedance loads.
Pulsed Power Conference, 2009. PPC '09. IEEE; 08/2009
-
D.J. Ampleford,
B. Jones,
C.A. Coverdale,
S.C. Jones,
M.C. Jones,
W.A. Stygar,
M.E. Savage,
K.R. LeChien,
C.A. Jennings,
M.E. Cuneo,
J.W. Thornhill,
J.L. Giuliani,
J.P. Apruzese,
K.G. Whitney,
R.W. Clark,
Y.K. Chong,
J. Davis,
A. Dasgupta,
J.P. Chittenden
[show abstract]
[hide abstract]
ABSTRACT: We present results from initial large diameter wire array experiments at the refurbished Z generator. 65mm on 32.5mm nested stainless steel wire arrays were fielded at two different total masses (2.5mg & 5mg). Each array was 20mm tall and had an inner array half the mass of the outer. The experiments were designed to evaluate trends in Fe K-shell power and yield and re-establish previous output, and large diameter tungsten wire arrays are further planned to study total x-ray output. For the 2.5mg nested stainless steel arrays the average total radiated yield measured with Ni bolometers was 1.9MJ. Peak powers of 250TW were inferred using the pulse shape from the Total Energy & Power diagnostic normalized to the bolometer yield. Using x-ray diodes for the pulse shape gave higher peak powers. Over three similar shots, the shot-to- shot variation was 6% in energy and 2.5% in peak power, well within the 30% systematic measurement error. Note that the shots described here were performed at 75% of the potential stored energy of the refurbished Z machine. We will compare the measured total yields and powers to the yields and powers from Stainless Steel and Tungsten arrays at various diameters on the Z generator both before and after the recent refurbishment. K-shell powers and yields were comparable to those from stainless steel experiments prior to the refurbishment, averaging 15TW and 60kJ. Data at 5mg confirmed the expected drop in the total power and K-shell power and yield due to L-shell radiative cooling at increased mass, however the total yield increased by 20% due to improved coupling to the generator.
Plasma Science - Abstracts, 2009. ICOPS 2009. IEEE International Conference on; 07/2009
-
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
[show abstract]
[hide abstract]
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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C A Coverdale,
A S Safronova,
V L Kantsyrev,
N D Ouart,
A A Esaulov,
C Deeney,
K M Williamson,
G C Osborne,
I Shrestha, D J Ampleford,
B Jones
[show abstract]
[hide abstract]
ABSTRACT: Experiments with cylindrical copper wire arrays at the 1-MA Zebra facility show that high temperatures exist in the precursor plasmas formed when ablated wire array material accretes on the axis prior to the stagnation of a z pinch. In these experiments, the precursor radiated approximately 20% of the >1000 eV x-ray output, and time-resolved spectra show substantial emission from Cu L-shell lines. Modeling of the spectra shows an increase in temperature as the precursor forms, up to approximately 450 eV, after which the temperature decreases to approximately 220-320 eV until the main implosion.
Physical Review Letters 04/2009; 102(15):155006. · 7.37 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: Highly collimated outflows or jets are produced by a number of
astrophysical objects including protostars. The morphology and
collimation of these jets is thought to be strongly influenced by the
effects of radiative cooling, angular momentum and the interstellar
medium surrounding the jet. Astrophysically relevant experiments are
performed with conical wire array z-pinches investigating each of these
effects. It is possible in each case to enter the appropriate parameter
regime, leading the way towards future experiments where these different
techniques can be more fully combined.
12/2008; 1088:83-88.
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S.C. Bott,
D.M. Haas,
Y. Eshaq,
U. Ueda,
S.V. Lebedev,
J.P. Chittenden,
J. Palmer,
S.N. Bland,
G.N. Hall, D.J. Ampleford,
F.N. Beg
[show abstract]
[hide abstract]
ABSTRACT: This paper investigates the ablation of wires in two-wire tungsten X -pinches driven by an 80-kA current over 50 ns. High-resolution imaging using a Nomarski interferometer allows measurements close to the X-pinch cross point, where the ablation ldquoflarerdquo structure is observed to clearly develop during the drive-current rise time. Electron density profiles are recovered as a function of both distance normal to the wire and of time. Results compare favorably to the rocket model of wire ablation. In addition, the density contrast over the ablation ldquostreamrdquo and ldquogaprdquo structure is measured and compared to similar measurements made using quantitative radiography on the 1-MA 250-ns MAGPIE generator at Imperial College London, London, U.K.
IEEE Transactions on Plasma Science 11/2008; · 1.17 Impact Factor
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D. B. Sinars,
S. A. Pikuz,
J. D. Douglass,
R. D. McBride, D. J. Ampleford,
P. Knapp,
K. Bell,
D. Chalenksi,
M. E. Cuneo,
J. B. Greenly,
D. A. Hammer,
B. R. Kusse,
A. Mingaleev,
T. A. Shelkovenko,
D. F. Wenger
[show abstract]
[hide abstract]
ABSTRACT: Bright, intense x-ray sources with extreme plasma parameters (micropinch plasmas) have previously been characterized at 0.1–0.4 MA, but the scaling of such sources at higher current is poorly understood. The x-ray source size and radiation power of 1 MA X pinches were studied as a function of wire material (Al, Ti, Mo, and W) and number (1-, 2-, 8-, 32-, and 64-wire configurations). The smallest bright spots observed were from 32-wire tungsten X pinches, which produced ⩽ 11–16 μm, ∼ 2 J, 1–10 GW sources of 3–5 keV radiation.
Physics of Plasmas 09/2008; 15(9):092703-092703-10. · 2.15 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: X-pinch radiography data are presented for wire array Z-pinches in which the wires initially have an imposed modulation. Calibrated data indicate a sharp contrast between the initially thicker regions of the wire, which remain intact, and the thinner regions which become fully depleted of material.
IEEE Transactions on Plasma Science 09/2008; · 1.17 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: Wire-array Z-pinches with low-density cylindrical foam targets on-axis have been used in inertial-confinement-fusion research on the 20-MA facility Z, but the effect of the targets on array performance is not fully understood. Experiments to investigate how the targets behave prior to array implosion, when they are bombarded by precursor plasma, have been carried out on the 1-MA MAGPIE generator. This paper presents data from X-pinch point-projection radiography, a primary diagnostic in these experiments.
IEEE Transactions on Plasma Science 09/2008; · 1.17 Impact Factor
-
B Jones,
C Deeney,
J L McKenney, D J Ampleford,
C A Coverdale,
P D Lepell,
K P Shelton,
A S Safronova,
V L Kantsyrev,
G Osborne,
V I Sotnikov,
V V Ivanov,
D Fedin,
V Nalajala,
F Yilmaz,
I Shrestha
[show abstract]
[hide abstract]
ABSTRACT: Axially localized NaF dopants are coated onto Al cylindrical wire arrays in order to act as spectroscopic tracers in the stagnated z-pinch plasma. Non-local-thermodynamic-equilibrium kinetic models fit to Na K-shell lines provide an independent measurement of the density and temperature that is consistent with spectroscopic analysis of K-shell emissions from Al and an alloyed Mg dopant. Axial transport of the Na dopant is observed, enabling quantitative study of instabilities in dense z-pinch plasmas.
Physical Review Letters 04/2008; 100(10):105003. · 7.37 Impact Factor
-
D J Ampleford,
S V Lebedev,
A Ciardi,
S N Bland,
S C Bott,
G N Hall,
N Naz,
C A Jennings,
M Sherlock,
J P Chittenden,
J B A Palmer,
A Frank,
E Blackman
[show abstract]
[hide abstract]
ABSTRACT: The first laboratory astrophysics experiments to produce a radiatively cooled plasma jet with dynamically significant angular momentum are discussed. A new configuration of wire array z pinch, the twisted conical wire array, is used to produce convergent plasma flows each rotating about the central axis. Collision of the flows produces a standing shock and jet that each have supersonic azimuthal velocities. By varying the twist angle of the array, the rotation velocity of the system can be controlled, with jet rotation velocities reaching approximately 18% of the propagation velocity.
Physical Review Letters 02/2008; 100(3):035001. · 7.37 Impact Factor
