As part of its science and national security missions, the U.S. Department of Energy National Nuclear Security Administration (DOE NNSA) supports a spectrum of basic and applied research in science and engineering at the agency's national laboratories, at universities and in industry.
Because of its continuing needs, NNSA has a special interest in encouraging development of the next generation of leaders in the following fields via the DOE NNSA LRGF program:
Solving critical science and engineering problems to enhance national and global security involves cutting edge research and the application of those research results coupled with technological innovation across a range of disciplines to create new capability and systems. This area focuses on applying pulsed power and accelerator technology (the storage and rapid delivery of large amounts of electrical energy) to produce relevant environments.
- Pulsed Power Technology: NNSA applies pulsed power technology across a range of science and engineering disciplines including complex hydrodynamics, material properties, atomic and plasma physics, and radiation and high energy density physics. Pulsed-power systems deliver megajoules of electrical energy in microsecond or nanosecond time scales, delivering terawatt powers and multi-megampere currents. NNSA develops superpower facilities such as Z at Sandia National Laboratories – facilities whose output equals or exceeds the total instantaneous electric-utility capacity of the globe – as “engines of discovery” that generate unprecedented states of matter in the laboratory for fusion technology and to address national and global security concerns. Research in pulsed power spans topics in traditional capacitive energy storage, switching, power conditioning and pulse shaping using capacitor banks, pulse lines and current-multiplying transformer technologies, magnetic compression, magnetic insulation, high-voltage breakdown, advanced static and dynamic electromagnetics, and industrial engineering applied to modular systems and may extend to inductive energy storage and some rotating machinery. Developing, modeling, and improving the performance and capability of these systems requires multi-disciplinary efforts in electrical engineering, plasma physics, mechanical engineering, high voltage electrical breakdown, and other fields.
- Particle Accelerators: NNSA offers theory, design, and experimental opportunities in all aspects of pulsed high-current electron beam accelerators used for X-radiography applications, low-current electron beam technology for radio-frequency accelerators, and advanced Free Electron Lasers (FEL). Penetrating imaging of dynamic, dense, objects requires intense pulses of high energy (>10 MeV) bremsstrahlung X-rays created by focusing kiloampere electron beam pulses to very small spot sizes (e.g. DARHT, FXR and others). Material science applications require radiation sources with flexible temporal and spectral characteristics (e.g. FELs) for use as probes in multi-scale material experiments with material scales ranging from atomic to macro-scale. Particle accelerator technology offers a new generation of engineers and physicists opportunities to work in traditional (pulse line and discrete-component pulsed power) and power electronic (solid-state) pulsed power drivers for linear induction accelerators. Candidates interested in plasma and electron-beam physics can explore the many challenging physics issues in beam stability, breakdown, surface plasmas, complex magnetic geometries and electromagnetics. Diagnostic physicists and engineers have opportunities to explore the latest (and yet to be invented) detectors, including the imaging, optics, recording and data transfer needed for advanced radiography.
Detailed understanding of the atomic physics of complex ions and of their interaction with radiation enhances our understanding of the evolution of complicated plasmas in both stellar objects and laboratory plasmas. The DOE NNSA LRGF seeks candidates interested in exploring both theoretical modeling and spectroscopic measurements of atoms, in both local thermodynamic equilibrium (LTE) and non-local thermodynamic equilibrium (NLTE) conditions.
- Local Thermodynamic Equilibrium : For LTE studies, in which system populations can be described with statistics, researchers model the system with exascale computing capabilities by writing new opacity codes with much more detailed atomic energy levels and physics. These codes are used to solve outstanding questions in astrophysics, such as radiation transport in the sun and the iron opacity problem. The latter refers to the result of recent experiments (“A higher-than-predicted measurement of iron opacity at solar interior temperatures,” J.E. Bailey, et. al., Nature 56, Vol. 517, January 2015) at the Sandia Z machine that measure an iron opacity that can explain radiation transport in the sun but is completely outside the scope of the best current opacity models.
- Non-Local Thermodynamic Equilibrium: For NLTE studies, system populations and resulting X-ray spectra are studied by solving rate equations between millions of levels. Accurate NLTE physics is crucial to developing predictive models of laboratory plasmas such as those dominating laser-to-X-ray conversion at the entrance hole in ICF hohlraums. High-quality experimental data across a spectrum of plasma conditions informs in-line models in radiation-hydrodynamic codes. New analysis techniques involving genetic algorithms and other sophisticated methods are being applied to benchmark the atomic physics codes to this data.
Advancing our understanding of complex systems that span multiple scales (temporal, spatial, spectral) and that engage multiple physics disciplines requires a balance of theoretical, computational, and experimental efforts. The DOE NNSA LRGF is seeking candidates who demonstrate the skills and potential to develop tools and capabilities in the following disciplines:
- Nuclear Astrophysics: Nuclear astrophysics focuses on the physics in systems ranging from the interior of stars to the formation of shocks at the edges of forming galaxies. Nuclear astrophysics encompasses a wide range of multi-physics topics including radiation hydrodynamics, shock physics, and nucleosynthesis, at scales from stellar to laboratory systems.
- Fluid Physics, including PIC-Fluid Hybrid Methods, Hydrodynamics, Instabilities and Shock Physics: When large amounts of energy are delivered to matter in short timescales, using a laser, particle beam, or pulsed power accelerator, material motion and shock waves are generated. Sufficient energy delivered to solid matter causes it to behave as a fluid. The equations of hydrodynamics model the subsequent motion of highly driven matter. Under such dynamic conditions matter is subject to a wide array of fluid instabilities that govern the behavior of that matter. The evolution of instabilities can be the subject of both simulations and experiments. The instability growth is often non-linear and therefore challenging to measure and model. These systems will also generate matter at numerous spatial and density scales, ranging from highly collisional, fluid-like behavior, to collisionless, kinetic-like behavior. Modeling and simulation methods that allow both fluid and kinetic limits to be treated self-consistently within the same framework, and self-consistently transition between them need to be developed.
- Laser-Plasma Interactions: A detailed understanding of the propagation of high-energy laser pulses in plasmas is essential to advance developments in inertial confinement fusion, laser-driven acceleration of relativistic charged particles, generation of neutrons, electrons and positrons, coherent and incoherent high-energy photon generation, and in advanced schemes of laser temporal compression and amplification.
- Radiation and Radiation Magneto-Hydrodynamics: The discipline of radiation-magneto-hydrodynamics (RMHD) is essential for the high-fidelity modeling of a variety of multi-dimensional, strongly coupled, and highly dynamical astrophysical, intense radiation source, and fusion systems. These systems require high-fidelity, self-consistent, and fully-coupled modeling of complex physical processes encompassing many decades of scale in both time and space. Interests include development and improvement of advanced numerical methods for RMHD, and experimental and simulation of turbulence and instabilities.
- Dynamics of Materials: Material properties in extreme conditions of pressure and temperature (0.1 to multi-Mbar, and room temperature to many tens of eV) are of critical importance for numerous scientific applications including shock physics, geoscience, astrophysics, inertial fusion, and national security applications. Experiments and simulations of phase transitions (solid-solid, solid-liquid), material structure, density, equation of state, constitutive and other properties are of interest.
The DOE NNSA LRGF program's primary objective is to encourage the training of scientists by providing financial support to talented students whose study and research is accompanied by practical work experience at one or more of the following DOE NNSA facilities: Lawrence Livermore National Laboratory, Los Alamos National Laboratory or Sandia National Laboratories (New Mexico), or at the Nevada National Security Site.