Bulletin of the American Physical Society
22nd Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 67, Number 8
Monday–Friday, July 11–15, 2022; Anaheim, California
Session V01: Melting and Re-solidificationFocus Recordings Available
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Chair: Jon Eggert, Lawrence Livermore Natl Lab Room: Anaheim Marriott Platinum 5 |
Thursday, July 14, 2022 2:00PM - 2:30PM |
V01.00001: Measuring the Melting Curve of Iron at Super-Earth Core Conditions by Dynamic Solidification Invited Speaker: Richard G Kraus The prominence of iron in planetary interiors requires accurate and precise physical properties at extreme pressure and temperature. A first-order property of iron is the melting point, which is still debated for the conditions of Earth’s interior. Using precisely tuned laser pulses at the National Ignition Facility we were able to shock melt samples of iron and then further shocklessly compress the iron to pressures of 5 and 10 Mbar. We used in-situ x-ray diffraction to directly observe dynamic solidification of iron into the hexagonal close packed structure on the nanosecond timescale. From these experiments we determine the criteria for solidification and ultimately the melting point of iron up to 1000 GPa, three times the pressure of Earth’s inner core [1]. |
Thursday, July 14, 2022 2:30PM - 2:45PM |
V01.00002: Multi-Mbar re-solidification of Pb on the nanosecond timescale at the National Ignition Facility Andrew Krygier, Amy E Lazicki, Richard G Kraus, Joel V Bernier, Gilbert W Collins, James M McNaney, J. Ryan Rygg, Raymond F Smith, Damian C Swift, Christopher Wehrenberg, Jon H Eggert Here we present results investigating high-pressure re-solidification of molten Pb on the nanosecond timescale. We have performed a series of experiments using the TARDIS platform at the National Ignition Facility (NIF) to measure x-ray diffraction of samples dynamically compressed to multi-Mbar pressure. Samples are initially shock compressed into the molten state, which is probed with x-ray diffraction. In the same experiment, the samples are then shocklessly compressed along the adiabat set by the initial shock pressure back into the solid state, which is probed with a second x-ray diffraction measurement. We report a series of experiments that provide a new constraint on the Pb melt curve up to ~6 Mbar as well as the crystal structure just below the melt curve. |
Thursday, July 14, 2022 2:45PM - 3:00PM |
V01.00003: Time Resolved Lattice Kinetics Of Rapidly Compressed Single Crystal Iron Through The alpha-epsilon Phase Transition James A Hawreliak, Stefan J Turneaure Experiments using broadband Laue x-ray diffraction (XRD) were used to examine the lattice structure of dynamically compressed [100]-oriented single crystal iron samples at the Dynamic Compression Sector at the Advanced Photon Source. These experiments used 1 micron thick iron single crystal samples sandwiched between a polyimide ablator and a polycarbonate window. A 40 J laser pulse incident on the polyimide ablator was used to shock or ramp compress the iron samples to stresses exceeding the ~13 GPa alpha to epsilon phase transition stress. XRD measurements of the lattice structure were performed at various times relative to the loading wave entering the iron sample. The shock measurements show that in less than ~150 ps the high-pressure hcp phase is relaxed with a c/a ratio of 1.61, contrary to previous laser shock experiments where a c/a ratio of 1.7 was inferred. In the ramp case in situ x-ray diffraction measurements show that a mixed alpha/epsilon phase was observed starting at ~13 GPa which persisted for ~2 ns until the peak stress of 18 GPa was reached. Similar to observations in shock-compression experiments, the epsilon phase formed with two dominant variants both with the epsilonphase c-axis orthogonal to the compression direction and a c/a ratio of 1.61. The bcc/hcp orientation relationships differ somewhat between dynamic and static compression experiments, implying that the transformation pathway under uniaxial dynamic strain differs from the Burgers mechanism. |
Thursday, July 14, 2022 3:00PM - 3:15PM |
V01.00004: Dynamic Measurements of the Al Melt Boundary Matthew T Beason, Brian J Jensen With the coupling of dynamic loading platforms with synchrotron light sources, shock melting has been shown to occur rapidly. Pyrometry is beginning to measure the melt line at high strain rates, providing data to compare to static measurements. However, there is limited information about density and kinetics along the melt line apart from shock melting. This talk will present results from shock-release experiments in pure Al shocked and release through states spanning 50-185 GPa. Velocity profiles measured at different sample thicknesses enable lagrangian analysis of release through the melt boundary and measurement on longitudinal wave speeds leading into shock melt. The results provide off-Hugoniot measurement of the melting phase transition leading into shock melting. |
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