Wednesday, September 9
Lawrence Livermore National Laboratory
If you were at the center of the planet, how strong would you be?
Asteroid impacts on planets, an imploding diamond capsule containing deuterium and tritium fuel for fusion, and the response of space hardware to hypervelocity interplanetary dust impacts are all examples of materials that we are familiar with being placed in conditions that were hitherto unreachable experimentally. In the past, radiation-hydrodynamic codes were used to simulate the material and system responses by extrapolating from physics based models based on limited experimental data. Validation of some of the physics-based models has been made possible by improvements in high energy density physics facilities in the past ~3 decades.
One such property that is of interest is a materials resistance to deformation which we define as being a material’s strength. In radiation hydrodynamics we model material response by creating a self-consistent Equation-of-State that relates the density and temperature of a liquid material to its volume, compressibility, pressure, specific heat, etc. Correctly simulating the response of solid materials has the increased complexity of modeling both the elastic response of a material in a regime where the energy applied to the material is not enough to permanently deform the material (elastic response) and the plastic deformation regime where energy is used to permanently deform the material. We commonly model solid materials in hydrodynamic codes by imposing strength models on top of liquid response equations that have been calibrated to reproduce the experimentally measured values such as deformation, sound speed, and melting.
Our materials group at LLNL has been conducting strength experiments on simple materials at multi-megabar (multi-Mbar) pressures using laser facilities in the United Kingdom (Orion), New York (Omega, LLE), and now at the National Ignition Facility at LLNL. We infer a materials resistance to deformation (strength) by applying a pressure history to a pre-imposed ripple on a Rayleigh-Taylor unstable interface, measure the growth of the material via transmission radiography, and then modify strength models used in radiation hydrodynamic simulations until the growth matches the measured value. I will discuss our experimental platform and briefly touch on results that we have obtained previously at the Omega laser facility on Ta and Cu at 1.5+ Mbar pressures. I will then detail some of the exciting results that we have recently seen at the National Ignition Facility for pressures up to 5+ Mbar and some of the multi-disciplinary challenges that we have had to overcome in order to begin our upcoming Pb experiments scheduled at NIF for 2016.
Wednesday, September 16
BYU CPMS Job Placement
Prepare for the Fair: The Elements of a Successful STEM Fair Experience
What’s the difference between a student who leaves the STEM fair with a couple of pens, a water bottle, and a bag of swag and a student who leaves with several scheduled job interviews? Come find out at the next Physics & Astronomy colloquium, where we’ll talk about how to prepare for and navigate the STEM fair. We’ll also discuss specific employers physics students should visit at the fair, as well as the new Career Fair Plus app.
Wednesday, September 23
Boise State University
We welcome anyone who wish to attend, and typically serve refreshments
ten minutes before the colloquium begins. Speakers generally keep
their presentation accessible to undergraduate physics students.