Speaker
Description
Certain planetary defense scenarios may require the use of nuclear explosive devices (NEDs) for successful mitigation [1]. Planning for these scenarios use engineering models derived from hydrocode simulations, themselves built upon models of x-ray energy deposition in asteroid material [2]. Recent work [3] has advanced the state-of-the-art in energy deposition modeling using radiation-hydrodynamics simulations. Though radiation-hydrodynamics processes begin to dominate at typical scenario x-ray fluences, the experimentally accessible x-ray fluences available at facilities such as OMEGA [4] are low enough that re-radiation of deposited energy is minimal, and cold opacities are sufficient to describe the x-ray energy deposition [5]. These levels are still sufficient to generate the material ablation and blowoff processes that serve as the momentum transfer mechanism in NED planetary defense scenarios, and are constrained by material-dependent properties.
In this work, we present a calibration of x-ray energy deposition models derived from broadband x-ray exposure experiments conducted at the OMEGA laser. Several geologic and meteoritic samples were exposed to various x-ray fluence levels over a multi-shot experimental campaign. On each shot, a specialized target [6,7] is illuminated by the OMEGA-60 laser system, generating a broadband flash of x-rays which irradiate the surfaces of the samples. Energy deposited by these x-rays initiate low-fluence ablation and blowoff processes. Following exposure, post-shot profilometry techniques are applied to determine the quantity of material removed in the experiment. The provides a key measurement of material removal depth, a quantity needed to calibrate ablation and impulse models. This low-fluence calibration in turn anchors radiation-hydrodynamics models and ties them to empirically accessible regimes.
This work was funded by a NASA Research Opportunities in Earth and Space Sciences (ROSES) 2022 Yearly Opportunities for Research in Planetary Defense (YORPD) grant (NASA Grant Number: 22-YORPD_22_2-0005) under the Near-Earth Object Observations Program. Part of this work was performed under the auspices of the Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. LLNL-ABS-871535.
[1] Dearborn, D.S.P. and P.L. Miller, “Defending Against Asteroids and Comets”, in Handbook of Cosmic Hazards and Planetary Defense (J.N. Pelton and F. Allahdadi, eds.), Ch. 34, pp. 733-754, Springer International Publishing Switzerland, 2015.
[2] Dearborn, D.S.P., M.B. Syal, et al., Options and Uncertainties in Planetary Defense: Impulse-Dependent Response and the Physical Properties of Asteroids, Acta Astronautica Vol. 183, pp. 29-42 (2021).
[3] Burkey, M.T., R.A. Managan, et al., X-Ray Energy Deposition Model for Simulating Asteroid Response to a Nuclear Planetary Defense Mitigation Mission, PSJ Vol. 4, p. 243 (2023).
[4] Davis, A.K., M.B. Airola, et al., Thermal Response Measurements for OMEGA-Laser-Generated Environments, JRERE Vol. 42 No. 1 pp. 35-40 (2024). (CUI Document.)
[5] King, P.K., D.M. Graninger, et al., Modeling the Dynamic Thermomechanical Response of Materials to X-Ray Irradiation, JRERE Vol. 42 No. 1 pp 41-49 (2024). (CUI Document.)
[6] Perez, F., J.J. Kay, et al., Efficient Laser-Induced 6-8 keV X-Ray Production from Iron Oxide Aerogel and Foil-Lined Cavity Targets, PoP 19, 083101 (2012).
[7] Girard, F., Review of Laser Produced Multi-keV X-Ray Sources from Metallic Foils, Cylinders with Liner, and Low Density Aerogels, PoP 23, 040501 (2016).