Lawrence Livermore National Laboratory


Investigation of Global climate models improvements over time
Benjamin Musci, Georgia Institute of Technology
Practicum Year: 2017
Practicum Supervisor: Karl Taylor, PCMDI-Program Director, Atmospheric, Earth, and Energy Division-PCMDI, Lawrence Livermore National Laboratory
This project consisted of data re-formatting and re-analysis. Global climate models have been around for over twenty years now, and the process by which the data from these models is output, presented, and organized has become increasingly standardized in recent years. This standardization increases the reliability and simplicity of making comparisons between models. My task was to reformat data from the old models so that they met the standards of the present day. This then allowed for the comparison of more recent models to older legacy models, which can tell us clearly whether or not they are improving over time.
Non-LTE Atomic Kinetics and Radiation Transport
Alison Saunders, University of California, Berkeley
Practicum Year: 2017
Practicum Supervisor: Howard Scott, Research Scientist, Weapons and Complex Integration- Design Physics, Lawrence Livermore National Laboratory
During my practicum, I learned to model radiation transport in plasmas that are relevant to astrophysical conditions. The first half of my practicum involved me learning a lot of new atomic physics that was required to understand how radiation transport worked. I learned about the models behind atomic structures, the rate equations of phototransitions, and the difference between systems in local thermodynamic equilibrium and in non-local thermodynamic equilibrium (nLTE). In parallel to learning that physics, I also learned how to use a nLTE code called CRETIN, which was originally developed by my practicum coordinator. Once I gained a basic fluency in radiation transport physics and CRETIN, I applied my skills to help design an experiment in photopumped atomic transitions for another Livermore group and collaborators at AWE.
Planetary Defense: Asteroid Deflection
Charles Epstein, Massachusetts Institute of Technology
Practicum Year: 2016
Practicum Supervisor: Dr. Paul Miller, Associate Division Leader, Design Physics Division, Lawrence Livermore National Laboratory
I worked on simulating gas-gun experiments, in which a pellet was impacted on a basalt target at high speed, in order to benchmark the ASPH code Spheral. By ensuring that Spheral can accurately reproduce controlled experiments, its use in simulating and quantifying asteroid impacts can be verified.
Fabrication and Thermal Testing of Graphene-Oxide/Carbon-Nanotube and Graphene-Oxide/3D-CVD Graphene Composite Aerogels
Nathan Finney, Columbia University
Practicum Year: 2016
Practicum Supervisor: Marcus A. Worsley, PhD, Staff Scientist, Advanced Materials Synthesis, Lawrence Livermore National Laboratory
Carbon-based aerogels tend to have a low thermal conductivity, but a reasonably high electrical conductivity (though nowhere near the intrinsic limit of pristine graphene), at mass densities comparable to Styrofoam, with extremely high porosity / surface area. Understanding how one can tune the thermal (and electrical) properties of these gels is a crucial step toward using them in advanced applications such as lightweight battery electrodes, or supercapacitor electrodes in energy storage systems (in spacecraft for example). As part of my practicum project, two separate fabrication procedures were explored for enhancing/tuning the thermal properties of graphene-oxide based aerogels. In the first procedure, single and double-walled carbon nanotubes were mixed in to the initial suspension of graphene-oxide at varying mass fractions relative to the initial aqueous graphene oxide concentration. Thermal testing was performed on these samples to detect an increase in mass density at comparable thermal conductivities as a function of carbon-nanotube concentration relative to the initial graphene oxide concentration. In the second procedure, an aqueous graphene-oxide and ammonium hydroxide (gelling agent) suspension was infilled into copper and nickel foams on which graphite and graphene was (respectively) grown via chemical vapor deposition (CVD). After gelation the metal foams were etched, and the remaining gels with percolating networks of multi and single layer graphene were super-critically dried and pyrolyzed. Thermal (and electrical) testing of materials prepared using the latter procedure are in progress. The motivation for exploring these two procedures was to generate a percolating network of atomically thin carbon structures with enhanced crystallinity within the graphene aerogel in an attempt to enhance conductive properties of the gel (either electrical, thermal, or both).
Additive manufacturing of functionally graded optical materials: developments towards a TiO2-SiO2 gradient index optical lens
Cameron Meyers, University of Minnesota
Practicum Year: 2016
Practicum Supervisor: Rebecca Dylla-Spears, Staff Scientist, Materials Science, Lawrence Livermore National Laboratory
Advances in additive manufacturing have created an opportunity to develop materials designed with functional gradients in chemical and physical properties. During my laboratory practicum I contributed to the development of an additively manufactured TiO2-SiO2 glass optical lens with a gradient in refractive index achieved by varying the ratio of TiO2 to SiO2. Chemical gradients can be designed such that a polished flat optic could be used as an aberration correcting plate, for example. The ability to customize axial and radial chemical gradients may allow designers to compensate for complex optical aberrations using fewer, more compact optics with lower finishing costs. We aimed to manufacture these optics using the direct ink write (DIW) additive manufacturing technique. We designed rheologically tuned colloidal/sol-gel suspensions containing TiO2-SiO2 glass precursors which could be extruded from a nozzle, dried, and sintered to transparent glass. Inks of various chemistries can be mixed in a mixing reservoir before extrusion to create gradients in refractive index in the final optic. The challenges of this manufacturing technique include development of an “ink” with rheology suitable for printing and mixing with other inks; learning how to avoid cracking of the part during drying; and making pieces with chemical and physical microstructure that sinters to transparency without trapping porosity or crystallizing secondary phases.
Intergranular HMX Frictional Modeling using ALE3D
Christopher Miller, Georgia Institute of Technology
Practicum Year: 2016
Practicum Supervisor: Dr. Laurence E. Fried, Reaction Dynamics Group Leader, Materials Science Division, Lawrence Livermore National Laboratory
This project involved creating a sliding model between two HMX (High Melting Explosive) grains that incorporated friction. With this setup, we were able to model how heat is generated in a crystal-based HMX material due to Coulomb friction and how this heat leads to the onset of chemical reactions. While this is just a small aspect of how energetic materials ignite, it is an important feature that is often overlooked in more mainstream models. ALE3D (LLNL's arbitrary Lagrangian-Eulerian 3D finite element modeling software) allowed me to combine a thoroughly tested HMX model and chemistry model in a way that hadn't been done before at LLNL.
Shear Viscosity of Asymmetric Strongly Coupled Dense Plasmas
Brooklyn Noble, University of Utah
Practicum Year: 2016
Practicum Supervisor: Dr. Robert Rudd, Computational Material Science Group Leader, Materials Science , Lawrence Livermore National Laboratory
Understanding transport processes in dense and strongly coupled plasmas is key to goals as deep and compelling as the attempt to create a limitless, carbon-free energy source through inertial confinement and the construction of galactic chronometers through white dwarf thermal decay rates. These processes include the transport of species (diffusion), momentum (viscosity), charge (electrical conductivity) and heat (thermal conductivity). Here we focus on viscosity and momentum transport. Conventional plasma theory is based on the kinetic theory of gases, which has been adapted to provide a good description of hot and rarefied plasmas. However, for relatively cold and dense plasmas, the spatial correlations of the ions matter, and kinetic theory fails. This behavior of the plasma is typically classified according to the coupling. As the temperature of a plasma is lowered, the plasma coupling increases and correlations become more important. The viscosity also increases because ion-ion interactions resist flow. Our goal was to study more strongly coupled plasmas and test the validity of previously developed hybrid models.
Actually Implicit Monte Carlo with High-Order Finite Element Meshes
Richard Vega, Texas A&M University
Practicum Year: 2016
Practicum Supervisor: Thomas A. Brunner, Kull Project Deputy Lead, Design Physics Devision, Lawrence Livermore National Laboratory
Implicit Monte Carlo is a trusted method for solving the thermal radiative transfer equations. The problem with Implicit Monte Carlo is that it is not implicit, only semi-implicit. Another problem with Implicit Monte Carlo is known as the "teleportation error" which results from assuming materials are piece-wise constant in each zone of the meshed geometry. This project aimed to fix these two problems by 1) implementing an non-linear iteration scheme to treat the emission source and material opacities implicitly and 2) representing the material properties in a finite element basis function expansion in order to give them some spatial profile within each zone.
Effect of Xenon Gas Fill Dopant in NIF Experiments
Io Kleiser, California Institute of Technology
Practicum Year: 2015
Practicum Supervisor: Laura Berzak Hopkins, , , Lawrence Livermore National Laboratory
The National Ignition Facility (NIF) uses high-powered lasers to implode a fuel capsule (usually isotopes of hydrogen) to high densities and temperatures in an effort to initiate fusion. While the primary goal is to achieve ignition, in which there is a self-propagating burn wave, there are non-ignition-scale experiments that can help inform ignition-scale experiments. Indirect drive exploding pusher (IDEP) experiments do not converge as much as ignition-scale experiments, but their implosions are much closer to spherical symmetry and relatively free of hydrodynamical instabilities, so they can more easily be compared to 1D simulations. These experiments can be used to better understand the early stages of the implosion. In order to probe the physical conditions in the capsule during these early stages, xenon can also be used as a dopant in the gas fill; however, even small amounts of xenon may significantly change the dynamics of the implosion. Running both experiments and 1D simulations of xenon-doped IDEP implosions in concert will help develop an understanding of the early stages of capsule implosion, an understanding which can then be applied to ignition-scale experiments.
Radiation hydrodynamics and particle-in-cell simulations of rapidly-heated buried-layers
Collin Stillman, University of Rochester
Practicum Year: 2015
Practicum Supervisor: Richard London, Physicist/Group Leader, AX, Lawrence Livermore National Laboratory
I worked with Dr. Richard London at Lawrence Livermore National Laboratory to learn how to model short-pulse laser heated solid targets. I learned how to
Cooling and Viscosity for Black Hole Accretion
Fabio Iunes Sanches, University of California, Berkeley
Practicum Year: 2014
Practicum Supervisor: Peter Anninos, , Astrophysics, Lawrence Livermore National Laboratory
The Cosmos++ code has the capability of simulating relativistic systems using a covariant formulation of magneto-hydrodynamic (MHD) equations. In particular, it can be a powerful tool in understanding accretion around neutron stars or rotating black holes. Such phenomena involve physical processes that occur on various length scales. In particular, the microscopic behavior of the accreting material has important long distance behavior that can modify its dynamics, which are driven by the metric describing the spacetime around the rotating black hole. These processes are not only difficult to account for, but also add to the computation time of simulations, making effective descriptions a powerful tool in these systems. The goal of the project was to expand the capabilities of Cosmos++ to include different cooling and viscosity contributions to the accretion disk. In addition, we also wanted to include a different formulation of the radiation components of the fluid.
Exploring the Self-Modulated Regime of Laser Wakefield Acceleration on the Titan Laser
Benjamin Galloway, University of Colorado, Boulder
Practicum Year: 2014
Practicum Supervisor: Bradley Pollock, Lawrence Postdoctoral Fellow, Jupiter Laser Facility, Lawrence Livermore National Laboratory
The project's goal was to explore a regime of laser wakefield acceleration (LWFA) that has not been investigated in depth. Specifically, the main objective was to measure the electron and betatron x-ray spectrum emitted in the self-modulated regime of LWFA. The Titan laser has ideal specifications for exploring this regime due to its relatively long pulse length (~1ps) and high pulse energy (up to 150J). A pulse with these specifications can be focused into a gas jet to produce plasma wakes, which consequently accelerate electrons to highly relativistic energies and wiggle them, producing betatron x-ray radiation. Due to the long pulse duration, the laser pulse extends into the plasma wake and can be modulated by the plasma frequency. Additionally, the accelerated electrons can be directly accelerated by this extended laser pulse. A secondary goal was to measure inverse Compton x-rays that can be generated by the interaction of the reflected laser pulse (off a foil) with the relativistic electrons in the wake.
Investigation of neutron star mass using the nuclear equation of state
Juan Manfredi, Michigan State University
Practicum Year: 2014
Practicum Supervisor: Rob Hoffman, Physicist, STE Physics, Lawrence Livermore National Laboratory
The nuclear equation of state plays a significant role in neutron star structure. Therefore, this equation can be constrained by neutron star measurements and calculations. Under the guidance of Peter Anninos and Rob Hoffman, I wrote a solver for the structural equations of the neutron star and also partially implemented a general framework for the Skyrme equation of state, which is based on nucleon-nucleon interaction. For this work I used COSMOS++, a code developed by Anninos and colleagues to do magnetohydrodynamics simulations that include general relativity.
Quantifying statistical and systematic uncertainties of the lattice equation of state
John Moreland, Duke University
Practicum Year: 2014
Practicum Supervisor: Ron Soltz, Dr., High Energy Accelerator Physics, Group Leader, Lawrence Livermore National Laboratory
The theory of the strong force is described by quantum chromodynamics (QCD) which admits analytic solutions in the limit of large momentum transfer where the QCD coupling constant is small and perturbative techniques become applicable. At typical scales of interest, the QCD coupling constant is not small and perturbative techniques fail. In these strongly coupled regimes, divergences are typically regulated on a space-time lattice. By substituting the real time coordinate with an "imaginary time", lattice discretization allows one to solve finite temperature QCD and extract the QCD equation of state. Lattice calculations are the only truly faithful description of strongly coupled QCD and are limited only by numerical mesh resolution and consequently the availability of computing resources. The HotQCD and Wuppertal-Budapest collaborations have independently calculated and published the lattice equation of state with corresponding statistical errors. Variances in the functional form of the QCD equation of state lead to variances in extracted values of fundamental QCD transport properties and thus are of great interest. In 2000, relativistic heavy-ion collisions revealed that super hot nuclear matter behaves like a perfect fluid with minimal viscosity. It thus became a task of great interest to extract the shear viscosity of this new state of matter which was dubbed a quark-gluon plasma. In my summer practicum with Ron Soltz, we've have analyzed and quantified the systematic and statistical errors of the lattice equation of state by comparing the collective flow and spectra of the state of the art HotQCD and Wuppertal-Budapest results. Our findings indicate that systematic uncertainties in the lattice equation of state contribute an order 5% uncertainty in the production of anisotropic flow, an observable used to constrain the QGP shear viscosity. In addition to the equation of state systematics, we are working on propagating the statistical errors of the HotQCD equation of state by analyzing the errors arising from the finite lattice spacing used in the calculation. We expect these statistical errors to be similar in magnitude to the systematics. These preliminary results suggest that the two major lattice calculations are consistent within the errors of the heavy-ion standard model and that throwing further CPU resources at refining the lattice equation of state will only marginally constrain relevant QCD observables.
Thermal conductivity measurements of proton-heated warm dense matter
Hong Sio, Massachusetts Institute of Technology
Practicum Year: 2014
Practicum Supervisor: Gilbert Collins, Shock physics group leader, High Energy Density Physics, Lawrence Livermore National Laboratory
I participated in the design and planning of an upcoming experiment in the Jupiter Laser Facility to measure thermal conductivity in warm dense matter (WDM). The measurements will be used to test current models for heat conduction in the strongly coupled plasma phase space and provide an experimental test of the Wiedemann-Franz law where electrical conductivity is used to infer thermal conductivity.
Monte Carlo Random Probability Analysis of 239Pu+48Ca
Sabrina Strauss, University of Notre Dame
Practicum Year: 2014
Practicum Supervisor: Nicholas Scielzo, , Physics, Lawrence Livermore National Laboratory
Element 114 (Fl), was discovered at the Flerov Laboratory of Nuclear Reactions (FLNR) using the 48Ca+244Pu reaction and the Dubna Gas-Filled Recoil Separator (DGFRS). Since it’s discovery, less than 100 atoms of Fl have been observed. The structural properties of the super heavy elements are still largely unknown. The extent of the region of enhanced stability near Z=114 and N=184 is not completely known. To examine these properties, a new experimental data set has been taken using the 48Ca +239Pu reaction at the DGFRS, in an effort to look for lighter isotopes of Fl. The low statistics of these experiments requires careful analysis to rule out background contribution. The data was analyzed using a monte carlo random probability technique to validate the results of analysis.
Accelerated Certification of Additively Manufactured Metals
John Gibbs, Northwestern University
Practicum Year: 2013
Practicum Supervisor: Wayne King, Director, ACAMM Initiative, Condensed Matter and Materials, Lawrence Livermore National Laboratory
The overall project is a multi-year, multi-million-dollar effort that is being done to improve LLNLs ability to rapidly produce high-quality metal parts via 3D printing. With current additive manufacturing knowledge and technology, it is relatively easy to quickly create plastic or metal parts; however, making a part that is high quality and doing so with enough confidence to put that part into service in a critical system is much more difficult. The focus of this project is to use a combination of simulations and experiments to expand the knowledge base of how the various processing parameters affect the final part properties.
A study of viscous incompressible flow interacting with flexible beams
Geoffrey Main, Stanford University
Practicum Year: 2013
Practicum Supervisor: Bill Henshaw, Applied Mathematician, Center for Applied Scientific Computing (CASC), Lawrence Livermore National Laboratory
I worked on coupling strategies for fluid-structure interaction on overset grids. Linear and nonlinear beam structural beam models were studied, and the conditions for stable and accurate coupling were analyzed.
Evaluation of Pulse Shape Discrimination Characteristics in 10Boron-Loaded Plastic Scintillators
Mareena Robinson, Massachusetts Institute of Technology
Practicum Year: 2013
Practicum Supervisor: Adam Bernstein, Advanced Detectors Group Leader, Physics , Lawrence Livermore National Laboratory
This investigation looked into the pulse shape discrimination characteristics of Boron-loaded plastic scintillators. Characteristics like relative light collection and the ability of the material to distinguish between particle types were tracked as sample compositions were varied.
Nuclear Magnetic Resonance Spectroscopy of Functionalized Mesoporous Silica with a Focus on Material Degradation in Acidic Environments and Complexation of Trivalent Metals
Jennifer Shusterman, University of California, Berkeley
Practicum Year: 2013
Practicum Supervisor: Annie Kersting, Dr., Physical and Life Sciences Directorate, Lawrence Livermore National Laboratory
The goal of my project was to understand the fundamental material properties of a few functionalized mesoporous silica materials that were synthesized by my research group at Berkeley. The ligand grafted to the silica was chosed because of its similarity to ligands used in the nuclear fuel cycle for trivalent actinides and lanthanides. While at LLNL, I studied these materials using Nuclear Magnetic Resonance (NMR) spectroscopy. First I thoroughly characterized the materials using solid-state 29Si and 13C NMR. Then I performed acid degradation experiments in which I contacted the functionalized mesoporous silica with various concentrations of nitric acid. I then collected 29Si and 13C NMR spectra again and by comparing them with the pristine samples was able to determine decomposition mechanisms for the solids. The most interesting part of my project was the metal complexation studies, in which the functionalized silica was contacted with either Al(III) or Sc(III) solutions in order to sorb these metals to the surface. Then, I was able to do either 27Al or 45Sc NMR to probe the metal nuclei themselves and determine the metal coordination numbers and whether they were binding to the silica surface or the ligand. This was especially interesting since the metals complexed to functionalized silica have rarely been probed directly based on the literature and it provides a new insight into binding mechanism which will allow for improvements to these materials. During my practicum, not only did I learn many interesting things about these materials, but also about a new technique. Prior to coming to LLNL, I had never used an NMR spectrometer myself. While I was at LLNL, I was able to learn about both solution state and solid state NMR spectroscopy. I focused mainly on solid-state NMR spectroscopy and became familiar with a variety of techniques and applications that I hope to apply to my future research.
12C Gamma Signal in NIF Capsules
Stephanie Lyons, University of Notre Dame
Practicum Year: 2012
Practicum Supervisor: Charles Cerjan, Physicist, WCI (Weapons Complex Integration), Lawrence Livermore National Laboratory
The gamma ray signature from 12C in the National Ignition Facility capsule output was studied to better understand how this could be measured using the existing nuclear diagnostic equipment on the NIF chamber. Since 12C is one of the elements used to create the NIF plastic capsules, which contain the dt-fuel used in the indirect drive experiments. Using neutron transport simulations, various types of situations could be investigated and analyzed to understand how deformity, doping, and density concentrations impact the 12C yield and the down-scattered ratio (DSR) of neutrons. The DSR is an important measure of the performance of each ignition shot. From the results of these simulations, cases with the correct DSR were selected and input into the Monte Carlo simulations of the gamma-ray history diagnostic (GRH). This is currently the first “source to detector” simulation that has been done on NIF. Analysis of the GRH simulation data is still under way.
Novel Searches for Sterile Neutrinos with Reactors and Spent Nuclear Fuel
Walter Pettus, University of Wisconsin, Madison
Practicum Year: 2012
Practicum Supervisor: Adam Bernstein, Group Leader, Advanced Detectors Group, Lawrence Livermore National Laboratory
Interest in sterile neutrinos has been fueled by anomalous signal hints observed in accelerator, solar, and reactor neutrino experiments. The recent reactor flux reanalysis leading to the "reactor antineutrino anomaly" has driven a wave of proposals to investigate this potential region of new physics. This practicum addressed sterile neutrino searches from source and reactor experiments. We created a flexible simulation capable of directly comparing the physics potential of proposed experiments of both types. A copy of this simulation code will be left with the laboratory group for further use. Its results have indicated the fragility of the source experiments and the probable importance of reactors in this next generation search. We also pursued the possibility of synthesizing a powerful (~500 kCi) 144Ce source from spent nuclear fuel or target irradiation. Our assessment, based on discussions with experts at the HFIR facility at Oak Ridge and NRU in Canada was that this path was not economically feasible with the present scope of reprocessing facilities in North America. The option for source experiments remains, but based on an unprocessed fuel source, where the backgrounds will require extensive further study.
Developing a Plasma Sheath Simulation Via the Kinetic Finite Mass Method
Christopher Young, Stanford University
Practicum Year: 2012
Practicum Supervisor: Dr. David J. Larson, Physicist, WCI-AX, Lawrence Livermore National Laboratory
This project aimed to create a plasma simulation tool based on the methodologies and sound mathematical foundation of the kinetic finite mass method. Developed to run efficiently in Fortran 90, the simulation tracks the evolution of continuous Gaussian "mass packets" in time under the influence of external and internal forces. We heavily investigated the particle "remap" process (in which new Gaussian mass packets are fit to a certain state of the data), built using a Gaussian Mixture Model enhanced by a hierarchical tree structure.
BOUT++ Simulations of Edge Turbulence in the Alcator C-Mod Tokamak
Evan Davis, Massachusetts Institute of Technology
Practicum Year: 2011
Practicum Supervisor: Xueqiao Xu, Physicist, MFE, Lawrence Livermore National Laboratory
Energy confinement in tokamaks is believed to be strongly controlled by plasma transport in the edge region just inside the last closed magnetic flux surface, and a first principles understanding of these edge processes is an active field of theoretical and experimental research. The Boundary-plasma Turbulence (BOUT++) code is capable of nonlinear fluid boundary turbulence analysis in a general geometry. Using experimentally measured profiles as input, BOUT++ calculations show that typical Alcator C-Mod EDA H-modes are ideal MHD stable, but become linearly unstable when the pedestal resistivity is included. The computed resistive ballooning mode growth rate in such shots is shown to scale approximately as the one-third power of plasma resistivity, consistent with theory. Inclusion of nonlinear effects in future simulations will allow for comparison with Alcator C-Mod fluctuation diagnostics.
1-D Calculation of the ITF Mix Exponent for Rev5 Ignition Targets
Michael Hay, Princeton University
Practicum Year: 2011
Practicum Supervisor: Larry Suter, Dr., AX, Lawrence Livermore National Laboratory
On the way to achieving ignition on the NIF, the National Ignition Campaign has found it useful to quantify the sensitivities of ignition targets to various deleterious effects that reduce margin and potentially yield. The primary metric used has been the Ignition Threshold Factor (ITF) [S. W. Haan, et al. Phys. Plasmas 18, 051001 (2011)], which is scaled to be the ratio of the DT fuel kinetic energy to the minimum kinetic energy required for ignition with the same fuel entropy and velocity. The ITF incorporates sensitivity to hydrodynamic instability at the fuel-ablator interface, which generates mix, as well as the sphericity and chemical purity of the central hot spot. Our project reevaluated the sensitivity of the current baseline ignition target to mix at the fuel-ablator interface. We used the radiation hydrodynamics code Hydra to perform 1-D implosion calculations that used a model to simulate the effects of mix without resorting to expensive 2- and 3-D calculations. The result of the project is a new ITF that suggests current targets could be more robust to the effects of mix than previously expected.
Design of an iron Rayleigh-Taylor laser experiment using radiation-hydrodynamics codes
Kristen John, California Institute of Technology
Practicum Year: 2011
Practicum Supervisor: Hye-Sook Park, Physicist, NIF Directorate, ICF and HED Science, Lawrence Livermore National Laboratory
My summer practicum at Lawrence Livermore National Laboratory (LLNL) involved learning how to design laser experiments used to study solid-state material properties of iron and other materials under high pressure and high strain rates. Additionally, my project included learning two new radiation-hydrodynamics (rad-hydro) codes, participating in several laser experiments on the Omega Laser at the Laboratory for Laser Energetics (LLE) at the University of Rochester, and analyzing data from these experiments. Also, the goal is to use this research as a platform for future experiments at Omega, which will form the basis of my research at Caltech.
Electron-Ion Equilibration in ICF plasmas
Alex Zylstra, Massachusetts Institute of Technology
Practicum Year: 2011
Practicum Supervisor: Gilbert Collins, , Physics, Lawrence Livermore National Laboratory
Electron-ion thermal equilibration in ICF plasmas is important in several scenarios. For example, propagating shocks preferentially heat ions and alpha self-heating preferentially deposits energy to the electrons. Understanding electron-ion equilibration at conditions where the traditional Spitzer rate is not valid, such as strongly-coupled degenerate plasmas, will be important for future studies of burning plasmas.
Development of an Improved Gas Ionization Detector for Isobaric Discrimination of Transition Metal Activation Products with Accelerator Mass Spectrometry
Matthew Buckner, University of North Carolina, Chapel Hill
Practicum Year: 2010
Practicum Supervisor: Scott Tumey, Scientific Staff, PLS/AEED/Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory
My practicum project was to take the actinide gas ionization detector developed by Scott Tumey at CAMS and simulate it in SimION and identify flaws within the original design. My goal was to then simulate, design, build, install and test a new gas ionization detector that corrects these flaws and is specifically designed for measuring the activation products of transition metals for nuclear forensics.
Remote Detection of Gammas and Neutrons with Cherenkov Detector: Coupling Simulation and Experiment
Anna Erickson (Nikiforova), Massachusetts Institute of Technology
Practicum Year: 2010
Practicum Supervisor: Adam Bernstein, Group Leader, Advanced Detectors Group, Advanced Detectors Group, Physical Sciences Div., Lawrence Livermore National Laboratory
During this practicum, I explored the applicability of water-based Cherenkov detectors (WCD) to signature high-energy gamma and neutron radiation from photofission of special nuclear materials (SNM). Such detectors face a dual challenge: being able to detect radiation remotely (50 meters or more away) and to reconstruct the information such radiation might be carrying. At high energies and in large (kiloton to multi-kiloton scale) water detectors, Cherenkov imaging is a well-proven technique. We are adapting this approach to the form factor we need at the lower energies encountered in SNM detection. Neutron detection is possible using WCDs through neutron capture on Gd and subsequent release of an 8 MeV gamma cascade. The reconstruction of gamma energies is difficult, making the separation of fission gammas from cascade gammas a challenge. Experimental data obtained with a one tonne detector doped with GdCl3 was compared with results predicted by simulation using Geant4. Similarities in pulse height spectrum shapes suggested that an energy calibration of WCDs is possible with neutron capture data and a Geant4 simulation.
Investigation of Phase Transitions on Release from Shock in H2O and SiO2
Richard Kraus, Harvard University
Practicum Year: 2010
Practicum Supervisor: Damian Swift, Dr., Physics, Lawrence Livermore National Laboratory
My practicum project utilized 3 weeks of time on the Janus laser at the Jupiter laser facility. There were two main goals of the project; the first was to explain a characteristic morphology of impact craters on icy planetary bodies by imaging the flow field behind divergent shock waves in H2O ice. To simulate an impact we focused the laser to a small spot size and used the 2D VISAR to image the velocity field behind the shock wave in the ice. The second main goal of the project was to determine the critical point of silica by shocking the silica into a supercritical fluid state and releasing to the liquid-vapor phase boundary. We measured shock wave velocities and temperatures in the quartz, and post-shock temperatures once the shock reached the free surface of the sample. For a subset of experiments, a LiF window was positioned downrange of the expanding silica. When the expanding silica impacts the LiF window, the velocity at the interface between the expanding silica and LiF window was measured using the VISAR. There were problems with the H2O ice targets and cryogenic system that we were not able to fix on the timescale of the experimental run and hence did not obtain any good data related to the first goal of imaging the flow field behind a divergent shock wave in H2O ice. We did obtain a large amount of good data on the release states of silica (reflecting shock waves in silica, shock and post-shock temperatures, and LiF interface velocities), which will require significant further analysis and comparisons to numerical models before any conclusions can be made about the liquid-vapor phase boundary or the critical point.
Analyzing Powers for 3H (d,n) 4He reactions in the NCSM+RGM model
Jordan McDonnell, University of Tennessee, Knoxville
Practicum Year: 2010
Practicum Supervisor: Erich Ormand, Dr., Group Leader, Nuclear Theory and Modeling, Lawrence Livermore National Laboratory
The deuterium-tritium (DT) fusion reaction has been the subject of extensive investigation because of its applications in energy, national defense, and astrophysics. Particularly for stellar fusion, terrestrial experiments have difficulty in probing the reaction's cross section at the relevant low energies. An ab initio theory -- a theory in which the only adjustable parameters are those for the interaction between nucleons -- for this reaction would provide an independent guide for extrapolating and evaluating experimental data in the appropriate energy range. We use the no-core shell model (NCSM) and resonating group method (RGM) in tandem to describe both internal nuclear structure and the collision between the two nuclei in a unified framework. It is well-known that the reaction cross section is enhanced when the spins of the deuterium and tritium nuclei are aligned. We calculate analyzing powers for polarized nuclei with the NCSM+RGM theory for the purposes of a systematic comparison between the theory's predictions and established experimental data.
Simulations for Optimizing the LLNL Negative Ion Time Projection Chamber (TPC)
Joshua Renner, University of California, Berkeley
Practicum Year: 2010
Practicum Supervisor: Adam Bernstein, Dr., Physical Sciences Division, Lawrence Livermore National Laboratory
The negative ion TPC ("time-projection chamber") is a detector being developed at Livermore that uses the particle detection technique called negative ion drift developed by C. J. Martoff et al. When an energetic particle interacts with a detector, its high energy removes electrons from the atoms in the detector medium. The more energy the particle has, the greater the number of electrons removed. In negative ion drift, the energy of a particle is measured by attaching these electrons to particles of gas, forming negative ions, and drifting these ions through an electric field to a region in which each electron can be removed from its ion and multiplied into a macroscopic signal. In this manner, each electron can be counted individually to determine how many electrons the original energetic particle produced and therefore its energy.
Neutron Time Projection Chamber
Patrick OMalley, Rutgers University
Practicum Year: 2009
Practicum Supervisor: Mike Heffner, Staff Scientist, Physics, Lawrence Livermore National Laboratory
Time projection chambers have been used for years in physics. At Lawrence Livermore National Lab , this group was trying to develop one to detect fast neutrons from special radioactive materials. One strength of this device over conventional neutron detectors is that it provides directional information of the source with only a single event. Of course, accuracy increases with more events. Another advantage is its insensitivity to gamma rays and its ability to do particle ID based on the ionization profile.
Spin state of Ferric Iron in Mg-Silicate Perovskite to 84 GPa
Krystle Catalli, Massachusetts Institute of Technology
Practicum Year: 2008
Practicum Supervisor: Hyunchae Cynn, Dr., High Pressure Physics, Lawrence Livermore National Laboratory
For my practicum project, I studied the electronic spin state of ferric iron in Mg-silicate perovskite, the most abundant mineral in the Earth's lower mantle. Mg-silicate perovskite composes approximately 80% of the Earth from 660 km to ~2900 km depth. As such, the properties of this mineral in the deep Earth have a great impact on the dynamics and history of the bulk Earth. However, due to its extreme stability field (pressures greater than 24 GPa), it cannot readily be sampled. So in order to measure the properties of Mg-silicate perovskite and the effects of pressure, temperature, and chemical composition, we synthesize the sample in the diamond anvil cell and measure its properties at in situ high temperature and pressure. My goal while working on my practicum project was to synthesize an iron-bearing Mg-silicate perovskite with all iron as ferric iron and measure the spin state of ferric iron in perovskite using X-ray emission spectroscopy at the Advanced Photon Source at Argonne National Laboratory through a collaboration with the High Pressure Physics Group at Lawrence Livermore National Laboratory. Because the relative ratio of ferric iron to ferrous iron in perovskite in the Earth is not known, it is important that we measure the properties of the endmember compositions.
HYDRA Simulations of Radiating Shock Experiments
Forrest Doss, University of Michigan
Practicum Year: 2008
Practicum Supervisor: Larry Suter, Dr., AX Division, Weapons and Complex Integration, Lawrence Livermore National Laboratory
The radiation hydrodynamics code HYDRA was developed at LLNL to simulate the physics of various experiments designed for and carried out at DOE facilities, particularly future fusion experiments for the National Ignition Facility. My work involved learning and applying HYDRA to radiating shock experiments, elucidating the results and data seen in a variety of shock experiments to date.
1. Ionic Conductivity in Complex Molecular Liquids at High Pressure, 2. Phase Separation in Hydrogen-Helium Mixtures
Miguel Morales, University of Illinois at Urbana-Champaign
Practicum Year: 2008
Practicum Supervisor: Eric Schwegler, Group Leader, Quantum Simulations Group, Lawrence Livermore National Laboratory
During my practicum in Lawrence Livermore National Laboratory (LLNL), I was involved in 3 projects: 1. The main project consists on the study of the ionic component of the electric conductivity in dense molecular liquids at very high pressures and intermediate temperatures. At these conditions molecules dissociate into their elementary components and traditional techniques used to calculate the electronic conductivity, based on the concentration of the different species and their diffusion, break down. I am currently applying and comparing several new techniques to measure the charge current and from it obtain the conductivity. 2. The second project consists in the study of hydrogen-helium mixtures at Mbar pressures and intermediate temperatures (4000K-10000K) using First-Principles Molecular Dynamics simulations with Density Functional Theory. Our main goal is to calculate the temperature, as a function of pressure, at which helium becomes insoluble in dense metallic hydrogen. We perform an extensive study of the equation of state of the mixture as a function of density, temperature, and composition and, together with a variety of thermodynamic integration techniques, we calculate the Gibbs free energy of mixing. 3. The third project consists on developing a new method to extrapolate wavefunctions during a DFT calculation from the result of a previously perform calculation on a similar system. All DFT-based ab-initio simulations are performed with Molecular Dynamics (MD) because in that case it is easy to formulate efficient methods that provide good starting wavefunctions for the DFT calculations, which is crucial to reduce the computational costs of the simulations. Monte Carlo (MC) provides an alternative way to perform ab-initio simulations, allowing us to calculate properties that are inaccessible to MD, but the lack of extrapolation techniques in this case has prevented its development and widespread use. I am developing a method that will allow me to perform the extrapolation efficiently and with it the use of DFT technology in MC calculations.
Quantum Correlations from Realistic NN Interactions
Angelo Signoracci, Michigan State University
Practicum Year: 2008
Practicum Supervisor: W. Erich Ormand, Group Leader, Nuclear Theory and Modeling Group, N-Division, Physical Sciences Directorate, Lawrence Livermore National Laboratory
Using Energy Density Functional (EDF) methods, I renormalized a realistic NN potential such as N3LO or Argonne v18 to the specific case of 68Ni in a chosen model space. I used Skyrme-Hartree-Fock to calculate the binding energy and single particle energies of 68Ni. The renormalized interaction was then used as an input to a configuration interaction (CI) calculation to produce level schemes of 67,68,69Ni, 67Co, and 69Cu for comparison to experiment and to the Skyrme binding energy. There is new experimental data causing these nuclei to be of interest to nuclear physics, and my calculations explored the reasons for the behavior. Additionally, after spending a few weeks on the practicum, I began to parallelize a shell model code in order to run it more efficiently on the LLNL supercomputers and improve calculation times by an order of magnitude.
A Proposal for Broadband Optical Characterization of Window Materials for HED Experiments
Dylan Spaulding, University of California, Berkeley
Practicum Year: 2008
Practicum Supervisor: Bruce Remington, Group Leader, HED Program, Y-Division (HED), Lawrence Livermore National Laboratory
My practicum task involved developing a proposal for an experiment which we hope to field in the coming year at LLNL. I have worked on developing a new diagnostic for laser-driven shock and ramp compression experiments that will enable optical characterization of materials at high pressures and temperatures with high time resolution. Laser-driven HED experiments, including many planned for the National Ignition Facility, rely on a tamping window (often LiF, MgO, SiO2 or similar) to maintain high pressure in the sample for the duration of the experiment and to prevent it from releasing directly into vacuum. Optical diagnostics observe the sample through this window, however the window's contribution to the measurements are often difficult or impossible to quantify. This is especially problematic when it comes to determining sample temperature, emissivity and for resolving anomalies in interferometry data. The frequency of use and importance of these materials to a variety of HED experiments thus motivates better characterization of their optical properties over a wide spectral band.