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Root, Seth

Publications and source records attributed to Root, Seth.

At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
DOE OSTI2012

Equation of state of CO 2 : experiments on Z, density functional theory (DFT) simulations, and tabular models

Over the last few years, first-principles simulations in combination with increasingly accurate shock experiments at multi-Mbar pressure have yielded important insights into how matter behaves under shock loading. Carbon dioxide (CO 2 ) is particularly interesting to study as a model molecular system for planetary science. Under high pressure - high temperature CO 2 dissociates and eventually begins ionizing. The dissociation pathway and the equation of state at extreme conditions is poorly understood. Cryogenic CO 2 is optically transparent while shocked CO 2 is metallic, displaying a reflective shock front, thus allowing for shock velocity measurement to very high precision. In this report, we present experimental results for shock compression of liquid cryogenic CO 2 to several Mbar using magnetically accelerated flyers on the Z machine, first-principles simulations based on Density Functional Theory including examining the CO 2 dissociation pathway, and an analysis of tabular equations of state (EOS) for CO 2 .

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2012

Equation of state of argon: experiments on Z, density functional theory (DFT) simulations, and wide-range model

Over the last few years, first-principles simulations in combination with increasingly accurate shock experiments at multi-Mbar pressure have yielded important insights into how matter behaves under shock loading. Noble gases like argon are particularly interesting to study as a model system due to the closed shell electronic structure that results in a weak interatomic interaction at normal conditions followed by pronounced ionization and strong interaction under compression. Cryo genic argon is also optically transparent while shocked argon is metallic, displaying a reflective shock front, thus allowing for shock velocity measurement to very high precision. In this report, we present experimental results for shock compression of liquid cryogenic argon to several Mbar using magnetically accelerated flyers on the Z machine, first-principles simulations based on Den sity Functional Theory, and an analysis of tabular equations of state (EOS) for argon, including a newly developed wide-range EOS model.

Carpenter, John H.↗
DOE OSTI2011

High-pressure shock behavior of WC and Ta2O5 powders.

Planar shock experiments were conducted on granular tungsten carbide (WC) and tantalum oxide (Ta{sub 2}O{sub 5}) using the Z machine and a 2-stage gas gun. Additional shock experiments were also conducted on a nearly fully dense form of Ta{sub 2}O{sub 5}. The experiments on WC yield some of the highest pressure results for granular materials obtained to date. Because of the high distention of Ta{sub 2}O{sub 5}, the pressures obtained were significantly lower, but the very high temperatures generated led to large contributions of thermal energy to the material response. These experiments demonstrate that the Z machine can be used to obtain accurate shock data on granular materials. The data on Ta{sub 2}O{sub 5} were utilized in making improvements to the P-{lambda} model for high pressures; the model is found to capture the results not only of the Z and gas gun experiments but also those from laser experiments on low density aerogels. The results are also used to illustrate an approach for generating an equation of state using only the limited data coming from nanoindentation. Although the EOS generated in this manner is rather simplistic, for this material it gives reasonably good results.

36 MATERIALS SCIENCE↗