Prof. Thomas Duffy
Ultra-High Pressure Dynamic Compression: Applications to the Deep Earth and Extra-Solar Planets
Laser-based dynamic compression provides new opportunities to study the properties of geological materials to ultra-high pressure conditions ranging up to 1000 GPa (1 TPa) and beyond. Such studies have fundamental applications to understanding the Earth’s deep interior as well as the interior structure of super-Earth and giant planets. This talk will review recent dynamic compression experiments using high-powered lasers on materials including Fe, Fe-Si, MgO, and SiC. Experiments were conducted at the Omega laser (University of Rochester) and the Linac Coherent Light Source (LCLS, Stanford). At Omega, ~5-10-ns laser pulses with energy up to 2 kJ are used to drive compression waves into geological samples. At peak compression, the sample is probed with quasi-monochromatic X-rays from a laser-plasma source and diffraction is recorded on image plates. At LCLS, shock waves are driven into the sample using a 40-J laser with a ~10-ns pulse. The sample is probed with X-rays form the LCLS free electron laser providing 1012 photons in a monochromatic pulse near 10 keV energy. Diffraction is recorded using pixel array detectors. By varying the delay between the laser and the x-ray beam, the sample can be probed at various times relative to the compression wave transiting the sample. By controlling the shape and duration of the incident laser pulse, either shock or ramp (shockless) loading can be produced. Ramp compression produces less heating than shock compression, allowing samples to be probed to ultrahigh pressures without melting. Results for iron alloys, oxides, and carbides provide new constraints on equations of state and phase transitions that are relevant to the interior structure of large, extrasolar terrestrial-type planets.
Bio: Thomas Duffy is a professor in the Department of Geosciences at Princeton University. He is also an affiliated faculty member in the Princeton Institute for the Science and Technology of Materials. Professor Duffy’s research interests focus on the physics and chemistry of geological materials at high pressures with applications to understanding the structure and dynamics of planets. Professor Duffy received his Ph.D. in Geophysics from the California Institute of Technology in 1992. He joined the Princeton faculty in 1997 after postdoctoral positions at the Carnegie Institution of Washington and the University of Chicago. He is a fellow of the American Geophysical Union, the Mineralogical Society of America, and the David and Lucile Packard Foundation.