Search

In magnetized liner inertial fusion (MagLIF), a cylindrical liner filled with fusion fuel is imploded with the goal of producing a one-dimensional plasma column at thermonuclear conditions. However, structures attributed to three-dimensional effects are observed in self-emission x-ray images. Despite this, the impact of many experimental inputs on the column morphology has not been characterized. We demonstrate the use of a linear regression analysis to explore correlations between morphology and a wide variety of experimental inputs across 57 MagLIF experiments. Results indicate the possibility of several unexplored effects. For example, we demonstrate that increasing the initial magnetic field correlates with improved stability. Although intuitively expected, this has never been quantitatively assessed in integrated MagLIF experiments. We also demonstrate that azimuthal drive asymmetries resulting from the geometry of the "current return can" appear to measurably impact the morphology. In conjunction with several counterintuitive null results, we expect the observed correlations will encourage further experimental, theoretical, and simulation-based studies. Finally, we note that the method used in this work is general and may be applied to explore not only correlations between input conditions and morphology but also with other experimentally measured quantities. [ABSTRACT FROM AUTHOR]

Reaching astrophysically relevant high energy density (HED) material states in the laboratory is an ongoing effort at multiple experimental facilities. We have developed a new dynamic compression platform for the Z Pulsed Power Facility that allows for sample sizes 100s of μ m in thickness that accommodate multiple grains in order to fully capture bulk properties, such as material strength. A pair of experiments compressed platinum (Pt) to HED conditions and conventional inverse Lagrangian analysis as well as a recent Bayesian calibration technique were used to determine the principal isentrope to 650 GPa with density uncertainties of <2%. These low uncertainties are calculated for single sample experiments, presenting the possibility of even smaller experimental uncertainties with multiple samples the platform allows. Our new platform extends the accessible Pt ramp pressures achievable on the Z machine to over 80% of the pressure recently achieved using the National Ignition Facility planar Hohlraum platform. This new capability, the next generation evolution of the stripline platform, was made possible by advancements in both our understanding of the Z pulsed power driver and our overall magnetohydrodynamic modeling capabilities. [ABSTRACT FROM AUTHOR]

This paper expands upon previous research into developing a numerical model of a capillary plasma source for application to electrothermal--chemical (ETC) guns. The capillary model is comprised of a kinetic model simulating polyethylene ablation coupled to a 1-D time-dependent hydrodynamic model to determine the capillary outflow parameters. As input, the simulation requires the capillary internal radius, length, and applied electrical current. Previous work found that best agreement with experimentally measured ablated mass could be achieved with the application of a backflux parameter, representing the percentage of the ablated material that was allowed to return to the polyethylene surface and form a film. Using the model, a parameter study is conducted to determine the effects that varying the peak electrical current, internal capillary radius, and backflux parameter has on the plasma temperature, peak outflow pressure, and total ablated mass. A sinusoidal electrical current is assumed in this paper, with the peak current and discharge time taken over a range typically encountered in ETC gun application. An analysis of the dependence of total ablated mass and peak capillary pressure on the deposited electrical energy yields insight into nonlinearities in the capillary energy equation. Index Terms--Capillary, electrothermal chemical (ETC), energy density, modeling.

Much progress has been made in the last few years toward the development of an end-to-end computer model of an electrothermal chemical gun. Phenomena that must be considered in an electrothermal chemical gun model include the initial capillary plasma properties, the plasma-air interaction, plasma sheath effects, and the plasma-propellant interaction itself. This paper presents an overview of recent progress made modeling these various phenomena. Also discussed are methods under consideration to incorporate surface chemistry effects into the plasma-propellant interaction model. Index Terms--Capillary, ETC, heat flux, modeling, plasma, plasma chemistry, plasma sheath.

Plasma-propellant interaction for application to an electrothermal gun is studied theoretically. Electrothermal-chemical (ETC) guns are used for enhancement of the ignition and combustion of the energetic propellant. A detailed understanding of the dynamics of the plasma-propellant interaction is considered one of the key elements to the future success of practical ETC gun implementation. A model of the propellant ablation under plasma effect is developed based on the kinetic theory of ablation. The ablation model is coupled with a model of the plasma generation in the capillary discharge that allows calculation of the effective heat flux from the plasma. Calculations are performed for specific experimental conditions in which ablated mass of a double-base and a nitramine composite propellant are studied. An ablation model is used to predict the ablation rate of the propellant for different bulk plasma densities. An effective heat flux from the plasma is found which yields the experimentally determined ablated mass. One representative solution reproduces the experimentally determined ablated mass for the double-base propellant of 5.3 mg via an effective heat flux on the order of 4 x [10.sup.8] J/[m.sup.2] s. The effective heat flux that corresponds to the experimentally measured ablated mass is determined for different propellants. Differences in the calculated effective heat flux between different propellants indicate that although heat convection from the plasma is the dominant source of energy, plasma radiation, and the optical properties of the propellants themselves cannot be ignored. The difference in plasma heat flux between propellants can readily be explained by partial absorption of plasma radiation consistent with the optical properties of the propellants. Index Terms--Electrothermal chemical (ETC), heat flux, modeling, plasma, propellant.

A closed-form solution is described here for the equilibrium configurations of the magnetic field in a simple heterogeneous domain. This problem and its solution are used for rigorous assessment of the accuracy of the ALEGRA code in the quasistatic limit. By the equilibrium configuration we understand the static condition, or the stationary states without macroscopic current. The analysis includes quite a general class of 2D solutions for which a linear isotropic metallic matrix is placed inside a stationary magnetic field approaching a constant value Hi° at infinity. The process of evolution of the magnetic fields inside and outside the inclusion and the parameters for which the quasi-static approach provides for self-consistent results is also explored. It is demonstrated that under spatial mesh refinement, ALEGRA converges to the analytic solution for the interior of the inclusion at the expected rate, for both body-fitted and regular rectangular meshes. [ABSTRACT FROM AUTHOR]