Plasma-driven Z-pinch X-ray loading and momentum coupling in meteorite and planetary materials

Abstract

X-ray momentum coupling coefficients, CM, were determined by measuring stress waveforms in planetary materials subjected to impulsive radiation loading from the Sandia National Laboratories Z-machine. Velocity interferometry (VISAR) diagnostics provided equation-of-state data. Targets were iron and stone meteorites, magnesium-rich olivine (dunite) solid and powder (~5–300 μm), and Si, Al, and Fe calibration targets. Samples were ~1-mm thick and, except for Si, backed by LiF single-crystal windows. X-ray spectra combined thermal radiation (blackbody 170–237 eV) and line emissions from pinch materials (Cu, Ni, Al, or stainless steel). Target fluences of 0.4–1.7 kJ/cm2 at intensities of 43–260GW/cm2 produced plasma pressures of 2.6–12.4 GPa. The short (~5 ns) drive pulses gave rise to attenuating stress waves in the samples. The attenuating wave impulse is constant, allowing accurate CM measurements from rear-surface motion. CM was 1.9 − 3.1 × 10−5 s/m for stony meteorites, 2.7 and 0.5 × 10−5 s/m for solid and powdered dunite, 0.8 − 1.4 × 10−5 s/m for iron meteorites, and 0.3, 1.8, and 2.7 × 10−5 s/m respectively for Si, Fe, and Al calibration targets. Results are consistent with geometric scaling from recent laser hohlraum measurements. CTH hydrocode modeling of X-ray coupling to porous silica corroborated experimental measurements and supported extrapolations to other materials. CTH-modeled CM for porous materials was low and consistent with experimental results. Analytic modeling (BBAY) of X-ray radiation-induced momentum coupling to selected materials was also performed, often producing higher CM values than experimental results. Reasons for the higher values include neglect of solid ejecta mechanisms, turbulent mixing of heterogeneous phases, variances in heats of melt/vaporization, sample inhomogeneities, wave interactions at the sample/window boundary, and finite sample/window sizes. The measurements validate application of CM to (inhomogeneous) planetary materials from high-intensity soft X-ray radiation.

High energy density soft X-ray momentum coupling to comet analogs for NEO mitigation

“…This work analyzes requirements for deflecting potentially hazardous comets with a high probability of Earth impact. It does so by extending previous research [1,2,3] on near-Earth asteroid (NEA) orbital deflection by high intensity pulsed X-rays and neutrons. Computational models simulate high power pulsed nuclear explosive radiation emission, target irradiation effects and subsequent surface blow-off ejection to generate momentum to modify orbits of near-Earth object (NEO) targets.…”

“…Also, recent reconnaissance of Pluto and its companions by the New Horizons mission suggests high energy radiative transfer work on primarily icy bodies is important for understanding early phases of solar system evolution when an active proto Sun emitted substantial amounts of ultraviolet and soft X-ray radiation. It also is important for comet NEO hazard mitigation where the X-ray driven surface plasma jetting of target materials from near surface (~ mm) layers provides recoil momentum critical for NEO orbital deflection of an Earth threatening object while minimally affecting the NEO structural integrity [1]. This applies to both comets and asteroids.…”

“…Therefore, laboratory studies of the stable mineral and physical structure of most meteorite types were used to interpret and model the physical properties of asteroids. This facilitated detailed material properties data input into computational modeling of NEAs as well as providing real asteroid target materials for high energy density experiments using the Sandia Z machine, which produces plasma generated Xrays that can be used to simulate nuclear explosive emissions [1].…”

Near-Earth Objects – The United Nations International Conference:Twenty Years Later

“…The orbital displacement was a mere 10 to 20 m/y, inconsequential for mitigation purposes. But this is no surprise and underscores the need for developing high energy payloads for mitigation [4]. Tempel 1 was revisited by the Stardust (reconnaissance) mission in 2011.…”

“…CTH hydrocode as applied to NEO interactions such as atmospheric entry, cratering and mitigation. A long term experimental analysis of the momentum and energy transfer effects of HED soft X-ray radiation on meteorites (as asteroid analogs) was concluded [4]. Simulations of and experimentation on HED mechanical and radiation interactions on putative NEO models is critical for a successful NEO mitigation mission.…”