This grant supports upgrade to the Caltech shock wave lab to allow for digital capture of projectile velocity and travel time of a shock in a solid or liquid sample. The high-speed Polaroid instant film currently used is no longer manufactured and their supply of the film is running low. In addition to a large-format CCD detector for the existing streak camera, other upgrades to the impact lab that will be supported include an X-ray image plate and scanning system for both of the large impact guns, a central breech to enable high-speed shots, fabrication of a new multichannel optical pyrometer, a Helium leak detector, a high-capacity piston-type vacuum pump, and a high-precision dual-range analytical balance. The requested enhancements will support NSF funded research on the characterization of the thermal Equation of State (EOS) of solid phases and liquid compositions of lower mantle phases and determination of the stability fields of these phases and measurement of the elasticity of transition metals at core conditions. The Caltech shock wave lab is unique in the U.S. academia as a lab dedicated to studying deep Earth geophysical problems with shock waves and the lab serves as an important training ground for the next generation geoscience and planetary science workforce.
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The Caltech shock wave lab is a unique facility that produces high-impact research in geophysics that could not be obtained anywhere else. We use a pair of large guns to create hypervelocity impacts under carefully controlled conditions, and to watch the response of materials such as rocks, minerals, magma, and metals to the resulting extreme conditions. The equipment purchased under this award enabled continued smooth operation and upgraded capabilities in imaging, gun operations and maintenance, and pyrometry. Specifically, the major equipment purchased under this award include: a CCD-based digital camera back to replace the film holder in our high-speed camera; CCD-based digitial cameras to replace the film holders for our dual-flash X-ray system to measure projectile velocities; a high-capacity vacuum pump to speed our preparation for each shot; a leak checker to ease diagnosis and repair of vacuum problems; and a replacement central breech that connects the two chambers of our two-stage gun. This equipment contributed directly to the achievement of the highest stable pre-heat temperatures ever documented in a shock experiment, allowing us to obtain new constraints on the melting curve and thermodynamics of MgO (an essential index mineral for understanding the Earth's lower mantle) and molten Mg2SiO4 (an essential endmember for the high-temperature early evolution of the Earth). Our data on the densities of molten rocks at extreme pressures form the benchmark for considerable experimental and theoretical efforts in geophysics, geochemistry, and planetary sciences. The intellectual merit of the project, and the research it continues to enable, lie in our understanding of the deep interior of our planet (and similar planets around other stars) and its evolution over time. We especially focus on the period very early in Earth history when most scientists believe the planet was largely or completely molten. The properties of molten rocks at pressures and temperatures that occur in the deep, early Earth are highly challenging to measure experimentally or to compute from reliable theories. Shock waves are one of the best ways to obtain these properties, which enable elaboration of much better-constrained scenarios for planetary evolution and tests of the predictions of those scenarios against observations in the geologic record or on the modern Earth. The broader imapcts of the project include enabling the training of Ph.D. students in cutting-edge laboratory research and the associated scientific questiosn and methods; training and retention of laboratory technicians to carry out all this work and maintain US leadership in this key area of research; and interaction with vendors and other labs (often US DOE national labs) to improve the equipment available for research and to share best practices in use of such equipment.
