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| Home > Monthly Bulletins > Scientists and their Lasers |
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| Scientists and their Lasers |
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| When Dr. Michael Murphy goes to work at Los Alamos National Laboratory he does what most can only dream of — he blows things up. |
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In fact, in the W-6 Detonator Technology group, Dr. Murphy and his colleagues make ultra-high-speed shock-wave measurements of detonator explosions.
Why measure the explosive output of a detonator from a shock-wave perspective? This work is essential to the understanding and development of newer, safer detonators.
So how do you get a job blowing things up? Michael began his studies at California State University Stanislaus receiving a Bachelor of Science degree in Physics. Using his newly-acquired knowledge of optics and lasers, he began a Masters degree in the Theoretical and Applied Mechanics department at the University of Illinois at Urbana-Champaign, where he began investigating explosive systems. He pursued his doctorate in the Laboratory for Energetic Flow and Turbulence at Arizona State University under the advisement of Prof. Ronald Adrian, and currently holds a postdoctoral position at Los Alamos.
Dr. Murphy investigates flows induced by explosions that are extreme in that they contain strong, curved shock waves moving at supersonic speeds. To this end, he has extended particle image velocimetry (PIV) methodology to measure the spatial and temporal evolution of shock and mass velocity with micron and nanosecond precision. His newest PIV system is capable of sampling a flow field eight times at up to 200 MHz. Integral to the success of the measurement is an eight-pulse PIV laser system.
Eight lasers are used to produce eight individual light sheets for making time-resolved PIV measurements. The laser system is configured as four dual-cavity PIV systems that are optically combined to produce eight co-linear beams. External combining optics provide user-controlled alignment capabilities, and each laser pulse is adjustable up to 100 mJ via manual attenuator control.
Recent experiments investigating detonator output demonstrate 20 MHz velocity-field sampling starting 300 ns after explosive initiation. The PIV measurements simultaneously quantify the velocity of the shocked medium and visualize the geometry of the shocked region This provides a novel means of characterizing detonator output.
Selected Publications of Dr. Michael Murphy
Murphy MJ, Adrian RJ (2010) PIV space-time resolution of flow behind blast waves. Accepted for publication in Exp Fluids
Murphy MJ, Adrian RJ (2010) PIV through moving shocks with curved geometry. Manuscript in review for Exp Fluids
Murphy MJ, Adrian RJ (2009) Characterizing detonator output using dynamic witness plates. In Proceedings of 16th APS Topical Conference on Shock Compression of Condensed Matter, Nashville, TN
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