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The study of local overheating and plasma formation on stainless steel z-pinch targets

Hatch, Maren W.; Awe, Thomas J.; Hutsel, Brian T.; Yu, Edmund Y.; Jauregui, Luis J.; Barrick, Erin J.; Gilmore, Mark A.

Plasma formation from intensely ohmically heated conductors is known to be highly non-uniform, as local overheating can be driven by micron-scale imperfections. Detailed understanding of plasma formation is required to predict the performance of magnetically driven physics targets and magnetically-insulated transmission lines (MITLs). Previous LDRD-supported work (projects 178661 and 200269) developed the electrothermal instability (ETI) platform, on the Mykonos facility, to gather high-resolution images of the self-emission from the non-uniform ohmic heating of z-pinch rods. Experiments studying highly inhomogeneous alloyed aluminum captured complex heating topography. To enable detailed comparison with magnetohydrodynamic (MHD) simulation, 99.999% pure aluminum rods in a z-pinch configuration were diamond-turned to ~10nm surface roughness and then further machined to include well-characterized micron-scale "engineered" defects (ED) on the rod's surface (T.J. Awe, et al., Phys. Plasmas 28, 072104 (2021)). In this project, the engineered defect hardware and diagnostic platform were used to study ETI evolution and non-uniform plasma formation from stainless steel targets. The experimental objective was to clearly determine what, if any, role manufacturing, preparation, or alloy differences have in encouraging nonuniform heating and plasma formation from high-current density stainless steel. Data may identify improvements that may be implemented in the fabrication/preparation of electrodes used on the Z machine. Preliminary data shows that difference in manufacturer has no observed effect on ETI evolution, stainless alloy 304L heated more uniformly than alloy 310 at similar current densities, and that stainless steel undergoes the same evolutionary ETI stages as ultra-pure aluminum, with increased emission tied to areas of elevated surface roughness.

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Stagnation Morphology in Magnetized Liner Inertial Fusion Experiments

Gomez, Matthew R.; Harding, Eric H.; Ampleford, David A.; Jennings, Christopher A.; Awe, Thomas J.; Chandler, Gordon A.; Glinsky, Michael E.; Hahn, Kelly D.; Hansen, Stephanie B.; Jones, Brent M.; Knapp, Patrick K.; Martin, Matthew; Peterson, Kyle J.; Rochau, G.A.; Ruiz, Carlos L.; Schmit, Paul S.; Sinars, Daniel S.; Slutz, Stephen A.; Weis, Matthew R.; Yu, Edmund Y.

Abstract not provided.

A Path to Increased Performance in Magnetized Liner Inertial Fusion

Gomez, Matthew R.; Slutz, Stephen A.; Jennings, Christopher A.; Harvey-Thompson, Adam J.; Weis, Matthew R.; Lamppa, Derek C.; Hutsel, Brian T.; Ampleford, David A.; Awe, Thomas J.; Bliss, David E.; Chandler, Gordon A.; Geissel, Matthias G.; Hahn, Kelly D.; Hansen, Stephanie B.; Harding, Eric H.; Hess, Mark H.; Knapp, Patrick K.; Laity, George R.; Martin, Matthew; Nagayama, Taisuke N.; Rovang, Dean C.; Ruiz, Carlos L.; Savage, Mark E.; Schmit, Paul S.; Schwarz, Jens S.; Smith, Ian C.; Vesey, Roger A.; Yu, Edmund Y.; Cuneo, M.E.; Jones, Brent M.; Peterson, Kyle J.; Porter, John L.; Rochau, G.A.; Sinars, Daniel S.; Stygar, William A.

Abstract not provided.

Direct observation of electrothermal instability structures in the skin layer of an intensely Ohmically heated conductor

Awe, Thomas J.; Yelton, William G.; Yu, Edmund Y.; Rosenthal, Stephen E.; McKenzie, Bonnie B.; Bauer, Bruno S.; Yates, Kevin C.; Hutchinson, Trevor M.; Fuelling, Stephan F.; Lowe, Daniel R.

Magnetically driven implosions (MDIs) on the Z Facility assemble high-energy-density plasmas for radiation effects and ICF experiments. MDIs are hampered by the Magneto-Rayleigh-Taylor (MRT) instability, which can grow to large amplitude from a small seed perturbation, limiting achievable stagnation pressures and temperatures. The metallic liners used in Magnetized Liner Inertial Fusion (MagLIF) experiments include astonishingly small (-10 nm RMS) initial surface roughness perturbations; nevertheless, unexpectedly large MRT amplitudes are observed in experiments. An electrothermal instability (ETI) may provide a perturbation which exceeds the initial surface roughness. For a condensed metal resistivity increases with temperature. Locations of higher resistivity undergo increased Ohmic heating, resulting in locally higher temperature, and thus still higher resistivity. Such unstable temperature (and pressure) growth produces density perturbations when the locally overheated metal changes phase, providing the seed perturbation for MRT growth. ETI seeding of MRT on thick conductors carrying current in a skin layer has thus far only been inferred by evaluating MRT amplitude late in the experiment. A direct observation of ETI is vital to ensure our simulation tools are accurately representing the seed of the deleterious MRT instability. In this LDRD project, ETI growth was directly observed on the surface of 1.0-mm-diameter solid Al rods which were pulsed with 1 MA of current in 100 ns. Fine structures resulting from ETI-driven temperature variations were observed directly through high resolution gated optical imaging. Data from two Aluminum alloys (6061 and 5N) and a variety fabrication techniques (conventional machining, single-point diamond turned, electropolished) enable evaluation of which imperfections provide a seed for ETI growth and subsequent plasma initiation. Data is relevant to the early stages of MagLIF liner implosions, when the ETI seed of MRT may be initiated, and provides a fundamentally new dataset with which to test our state-of-the-art simulation tools.

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Modified 3D-helix-like instability structure for imploding Z-pinch liners that are premagnetized with a uniform axial field

Awe, Thomas J.; Jennings, Christopher A.; McBride, Ryan D.; Cuneo, M.E.; Lamppa, Derek C.; Martin, Matthew; Rovang, Dean C.; Sinars, Daniel S.; Slutz, Stephen A.; Owen, Albert C.; Gomez, Matthew R.; Hansen, Stephanie B.; Harding, Eric H.; Herrmann, Mark H.; Jones, Michael J.; Knapp, Patrick K.; Mckenney, John M.; Peterson, Kyle J.; Robertson, Grafton K.; Rochau, G.A.; Savage, Mark E.; Schmit, Paul S.; Sefkow, Adam B.; Stygar, William A.; Vesey, Roger A.; Yu, Edmund Y.; Tomlinson, Kurt T.; Schroen, Diana G.

Abstract not provided.

Pulsed-power driven inertial confinement fusion development at Sandia National Laboratories

Proposed for publication in 5th Special Issue of the IEEE Transactions on Plasma Science Z-Pinch Plasmas.

Cuneo, M.E.; Mazarakis, Michael G.; Lamppa, Derek C.; Kaye, Ronald J.; Nakhleh, Charles N.; Bailey, James E.; Hansen, Stephanie B.; McBride, Ryan D.; Herrmann, Mark H.; Lopez, A.; Peterson, Kyle J.; Ampleford, David A.; Jones, Michael J.; Savage, Mark E.; Jennings, Christopher A.; Martin, Matthew; Slutz, Stephen A.; Lemke, Raymond W.; Christenson, Peggy J.; Sweeney, Mary A.; Jones, Brent M.; Yu, Edmund Y.; McPherson, Leroy A.; Harding, Eric H.; Knapp, Patrick K.; Gomez, Matthew R.; Awe, Thomas J.; Stygar, William A.; Leeper, Ramon J.; Ruiz, Carlos L.; Chandler, Gordon A.; Mckenney, John M.; Owen, Albert C.; McKee, George R.; Matzen, M.K.; Leifeste, Gordon T.; Atherton, B.W.; Vesey, Roger A.; Smith, Ian C.; Geissel, Matthias G.; Rambo, Patrick K.; Sinars, Daniel S.; Sefkow, Adam B.; Rovang, Dean C.; Rochau, G.A.

Abstract not provided.

Spectroscopic study of z-pinch stagnation on Z

Rochau, G.A.; Bailey, James E.; Coverdale, Christine A.; Ampleford, David A.; Cuneo, M.E.; Jones, Brent M.; Jennings, Christopher A.; Yu, Edmund Y.; Hansen, Stephanie B.

Fast z-pinches provide intense 1-10 keV photon energy radiation sources. Here, we analyze time-, space-, and spectrally-resolved {approx}2 keV K-shell emissions from Al (5% Mg) wire array implosions on Sandia's Z machine pulsed power driver. The stagnating plasma is modeled as three separate radial zones, and collisional-radiative modeling with radiation transport calculations are used to constrain the temperatures and densities in these regions, accounting for K-shell line opacity and Doppler effects. We discuss plasma conditions and dynamics at the onset of stagnation, and compare inferences from the atomic modeling to three-dimensional magneto-hydrodynamic simulations.

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Scaling of X pinches from 1 MA to 6 MA

Sinars, Daniel S.; McBride, Ryan D.; Wenger, D.F.; Cuneo, M.E.; Yu, Edmund Y.; Harding, Eric H.; Hansen, Stephanie B.; Ampleford, David A.; Jennings, Christopher A.

This final report for Project 117863 summarizes progress made toward understanding how X-pinch load designs scale to high currents. The X-pinch load geometry was conceived in 1982 as a method to study the formation and properties of bright x-ray spots in z-pinch plasmas. X-pinch plasmas driven by 0.2 MA currents were found to have source sizes of 1 micron, temperatures >1 keV, lifetimes of 10-100 ps, and densities >0.1 times solid density. These conditions are believed to result from the direct magnetic compression of matter. Physical models that capture the behavior of 0.2 MA X pinches predict more extreme parameters at currents >1 MA. This project developed load designs for up to 6 MA on the SATURN facility and attempted to measure the resulting plasma parameters. Source sizes of 5-8 microns were observed in some cases along with evidence for high temperatures (several keV) and short time durations (<500 ps).

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Three-dimensional effects in trailing mass in the wire-array Z pinch

Physics of Plasmas

Yu, Edmund Y.; Cuneo, M.E.; Desjarlais, Michael P.; Lemke, Raymond W.; Sinars, Daniel S.; Haill, Thomas A.; Waisman, E.M.; Bennett, G.R.; Jennings, C.A.; Mehlhorn, T.A.; Brunner, T.A.; Hanshaw, H.L.; Porter, J.L.; Stygar, W.A.; Rudakov, L.I.

The implosion phase of a wire-array Z pinch is investigated using three-dimensional (3D) simulations, which model the mass ablation phase and its associated axial instability using a mass injection boundary condition. The physical mechanisms driving the trailing mass network are explored, and it is found that in 3D the current paths though the trailing mass can reduce bubble growth on the imploding plasma sheath, relative to the 2D (r,z) equivalent. Comparison between the simulations and a high quality set of experimental radiographs is presented. © 2008 American Institute of Physics.

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One-dimensional ablation in multiwire arrays

Proposed for publication in Physics of Plasmas.

Yu, Edmund Y.; Oliver, Bryan V.; Mehlhorn, Thomas A.

The main physical processes responsible for plasma ablation in multiwire Z pinches are considered via eigensolutions to one-dimensional steady state magnetohydrodynamics. A double scale-length structure of the plasma accelerating layer is demonstrated. The width of the resistive scale-length that defines the current layer structure is significantly larger than the thermal scale-length, where transport of energy toward the cores and plasma pressure play important roles. The transport of energy is provided mainly by radiation, though electron thermal conduction is also important very close to the plasma-core interface. Another type of solution of the steady state problem is revealed, when local Ohmic heating is important down to the interface. Selection between these two types of solutions is considered from multiple points of view. Although the one-dimensional problem is mainly considered in this paper, it is shown how the one-dimensional results may help to understand results of two-dimensional models.

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Linear and nonlinear evolution of azimuthal clumping instabilities in a Z-pinch wire array

Physics of Plasmas

Tang, Wilkin; Strickler, T.S.; Lau, Y.Y.; Gilgenbach, R.M.; Zier, Jacob; Gomez, M.R.; Yu, Edmund Y.; Garasi, Christopher J.; Cuneo, M.E.; Mehlhorn, Thomas A.

This paper presents an analytic theory on the linear and nonlinear evolution of the most unstable azimuthal clumping mode, known as the pi-mode, in a discrete wire array. In the pi-mode, neighboring wires of the array pair-up as a result of the mutual attraction of the wires which carry current in the same direction. The analytic solution displays two regimes, where the collective interactions of all wires dominate, versus where the interaction of the neighboring, single wire dominates. This solution was corroborated by two vastly different numerical codes which were used to simulate arrays with both high wire numbers (up to 600) and low wire number (8). All solutions show that azimuthal clumping of discrete wires occurs before appreciable radial motion of the wires. Thus, absence of azimuthal clumping of wires in comparison with the wires' radial motion may imply substantial lack of wire currents. While the present theory and simulations have ignored the plasma corona and axial variations, it is argued that their effects, and the complete account of the three-dimensional feature of the pi-mode, together with a scaling study of the wire number, may be expediently simulated by using only one single wire in an annular wedge with a reflection condition imposed on the wedge's boundary. © 2007 American Institute of Physics.

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Towards a predictive MHD simulation capability for designing hypervelocity magnetically-driven flyer plates and PWclass z-pinch x-ray sources on Z and ZR

Mehlhorn, Thomas A.; Yu, Edmund Y.; Vesey, Roger A.; Cuneo, M.E.; Jones, Brent M.; Knudson, Marcus D.; Sinars, Daniel S.; Robinson, Allen C.; Trucano, Timothy G.; Brunner, Thomas A.; Desjarlais, Michael P.; Garasi, Christopher J.; Haill, Thomas A.; Hanshaw, Heath L.; Lemke, Raymond W.; Oliver, Bryan V.; Peterson, Kyle J.

Abstract not provided.

Progress in symmetric ICF capsule implosions and wire-array z-pinch source physics for double z-pinch driven hohlraums

Proposed for publication in Plasma Physics and Controlled Fusion.

Cuneo, M.E.; Nash, Thomas J.; Yu, Edmund Y.; Mehlhorn, Thomas A.; Matzen, M.K.; Vesey, Roger A.; Bennett, Guy R.; Sinars, Daniel S.; Stygar, William A.; Rambo, Patrick K.; Smith, Ian C.; Bliss, David E.

Over the last several years, rapid progress has been made evaluating the double-z-pinch indirect-drive, inertial confinement fusion (ICF) high-yield target concept (Hammer et al 1999 Phys. Plasmas 6 2129). We have demonstrated efficient coupling of radiation from two wire-array-driven primary hohlraums to a secondary hohlraum that is large enough to drive a high yield ICF capsule. The secondary hohlraum is irradiated from two sides by z-pinches to produce low odd-mode radiation asymmetry. This double-pinch source is driven from a single electrical power feed (Cuneo et al 2002 Phys. Rev. Lett. 88 215004) on the 20 MA Z accelerator. The double z-pinch has imploded ICF capsules with even-mode radiation symmetry of 3.1 {+-} 1.4% and to high capsule radial convergence ratios of 14-21 (Bennett et al 2002 Phys. Rev. Lett. 89 245002; Bennett et al 2003 Phys. Plasmas 10 3717; Vesey et al 2003 Phys. Plasmas 10 1854). Advances in wire-array physics at 20 MA are improving our understanding of z-pinch power scaling with increasing drive current. Techniques for shaping the z-pinch radiation pulse necessary for low adiabat capsule compression have also been demonstrated.

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Mass profile and instability growth measurements for 300-wire z-pinch implosions driven by 14-18, MA

Proposed for publication in Physical Review Letters.

Sinars, Daniel S.; Cuneo, M.E.; Yu, Edmund Y.; Bliss, David E.; Nash, Thomas J.; Deeney, Christopher D.; Mazarakis, Michael G.; Wenger, D.F.

We present the first comprehensive study of high wire-number, wire-array Z-pinch dynamics at 14-18 MA using x-ray backlighting and optical shadowgraphy diagnostics. The cylindrical arrays retain slowly expanding, dense wire cores at the initial position up to 60% of the total implosion time. Azimuthally correlated instabilities at the array edge appear during this stage which continue to grow in amplitude and wavelength after the start of bulk motion, resulting in measurable trailing mass that does not arrive on axis before peak x-ray emission.

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[Copy of characteristics and scaling of tungsten-wire-array z-pinch implosion dynamics at 20 MA.]

Proposed for publication in Physics of Plasmas.

Vesey, Roger A.; Yu, Edmund Y.; Nash, Thomas J.; Bliss, David E.; Bennett, Guy R.; Sinars, Daniel S.; Simpson, Walter W.; Ruggles, Larry R.; Wenger, D.F.; Garasi, Christopher J.; Aragon, Rafael A.; Fowler, William E.; Johnson, Drew J.; Keller, Keith L.; McGurn, John S.; Mehlhorn, Thomas A.; Speas, Christopher S.; Struve, Kenneth W.; Stygar, William A.; Chandler, Gordon A.

Abstract not provided.

Scaling of high-mass tungsten-wire-array z-pinch discrete-wire implosion dynamics at 20 MA

Proposed for publication in Physical Review Letters.

Cuneo, M.E.; Yu, Edmund Y.; Garasi, Christopher J.; Oliver, Bryan V.; Aragon, Rafael A.; Bliss, David E.; Lazier, Steven E.; Mehlhorn, Thomas A.; Nielsen, D.S.; Sarkisov, Gennady S.; Cuneo, M.E.; Vesey, Roger A.; Wagoner, Tim C.; Chandler, Gordon A.; Waisman, Eduardo M.; Stygar, William A.; Nash, Thomas J.; Yu, Edmund Y.

Abstract not provided.

76 Results
76 Results