Fundamental studies on the electrothermal instability on the 1 MA Mykonos driver
Abstract not provided.
Publications
Using engineered defects to understand the seed for instabilities in current-driven metal
Abstract not provided.
Three-dimensional metal deformation and plasma formation driven by resistive inclusions
Abstract not provided.
Diagnostics to study electrothermal instabilities on Mykonos
Abstract not provided.
Auto-Magnetizing Helical Liners: Megagauss-Level Premagnetization in Pulsed Power Magneto-Inertial Fusion
Abstract not provided.
Megagauss-level magnetic field and dielectric breakdown measured in auto-magnetizing liner experiments
Abstract not provided.
Auto-magnetizing liners for magneto-inertial fusion experiments
Abstract not provided.
Experimental observation of the stratified electrothermal instability on aluminum with thickness greater than a skin depth
Physical Review E
A direct observation of the stratified electrothermal instability on the surface of thick metal is reported. Aluminum rods coated with 70μm Parylene-N were driven to 1 MA in 100ns, with the metal thicker than the skin depth. The dielectric coating suppressed plasma formation, enabling persistent observation of discrete azimuthally correlated stratified thermal perturbations perpendicular to the current whose wave numbers, k, grew exponentially with rate γ(k)=0.06ns-1-(0.4ns-1μm2rad-2)k2 in ∼1g/cm3, ∼7000K aluminum.
Megagauss-level magnetic field production in cm-scale auto-magnetizing helical liners pulsed to 500 kA in 125 ns
Physics of Plasmas
Auto-magnetizing (AutoMag) liners [Slutz et al., Phys. Plasmas 24, 012704 (2017)] are designed to generate up to 100 T of axial magnetic field in the fuel for Magnetized Liner Inertial Fusion [Slutz et al., Phys. Plasmas 17, 056303 (2010)] without the need for external field coils. AutoMag liners (cylindrical tubes) are composed of discrete metallic helical conduction paths separated by electrically insulating material. Initially, helical current in the AutoMag liner produces internal axial magnetic field during a long (100 to 300 ns) current prepulse with an average current rise rate d I / d t = 5 k A / n s. After the cold fuel is magnetized, a rapidly rising current (200 k A / n s) generates a calculated electric field of 64 M V / m between the helices. Such field is sufficient to force dielectric breakdown of the insulating material after which liner current is reoriented from helical to predominantly axial which ceases the AutoMag axial magnetic field production mechanism and the z-pinch liner implodes. Proof of concept experiments have been executed on the Mykonos linear transformer driver to measure the axial field produced by a variety of AutoMag liners and to evaluate what physical processes drive dielectric breakdown. A range of field strengths have been generated in various cm-scale liners in agreement with magnetic transient simulations including a measured field above 90 T at I = 350 kA. By varying the helical pitch angle, insulator material, and insulator geometry, favorable liner designs have been identified for which breakdown occurs under predictable and reproducible field conditions.
Development of the striation and filament form of the electrothermal instability
Abstract not provided.
Direct observation of electrothermal instability structures in the skin layer of an intensely Ohmically heated conductor
Abstract not provided.
Electrothermal Instability Evolution on Z-Pinch Rods and Imploding Liners Pulsed with Intense Current
Abstract not provided.
Electrothermal Instability Evolution on Z-Pinch Rods and Imploding Liners Pulsed with Intense Current
Abstract not provided.
On the evolution from micrometer-scale inhomogeneity to global overheated structure during the intense joule heating of a z-pinch rod
IEEE Transactions on Plasma Science
Ultrafast optical microscopy of metal z-pinch rods pulsed with megaampere current is contributing new data and critical insight into what provides the fundamental seed for the magneto-Rayleigh-Taylor (MRT) instability. A two-frame near infrared/visible intensified-charge-coupled device gated imager with 2-ns temporal resolution and 3-μm spatial resolution captured emissions from the nonuniformly Joule heated surfaces of ultrasmooth aluminum (Al) rods. Nonuniform surface emissions are consistently first observed from discrete, 10-μm scale, subelectronvolt spots. Aluminum 6061 alloy, with micrometer-scale nonmetallic resistive inclusions, forms several times more spots than 99.999% pure Al 5N; 5-10 ns later, azimuthally stretched elliptical spots and distinct strata (40-100μm wide by 10μm tall) are observed on Al 6061, but not on Al 5N. Such overheat strata, which are aligned parallel to the magnetic field, are highly effective seeds for MRT instability growth. These data give credence to the hypothesis that early nonuniform Joule heating, such as the electrothermal instability, may provide the dominant seed for MRT.
ETI Growth under Dielectric Coatings
Abstract not provided.
15 Results