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, the NNSA seeks candidates who demonstrate the skills and potential to form 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 the resulting knowledge, coupled with technological innovation across a range of disciplines to create new capabilities 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 on microsecond or nanosecond time scales, carrying terawatt powers and multi-megampere currents. NNSA develops superpower facilities such as Sandia National Laboratories’ Z – devices whose output equals or exceeds the total instantaneous electric-utility capacity of the globe – as engines of discovery. They produce unprecedented states of matter in the laboratory for fusion technology and to address national and global security concerns. Pulsed-power research includes 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. Research also 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 and modeling, accelerator design, and experimental research opportunities in all aspects of pulsed high-current electron beam accelerators for X-radiography, for low-current electron beam technology in radio-frequency accelerators, and in advanced Free Electron Lasers (FEL). Penetrating imaging of dynamic, dense objects requires intense pulses of high-energy (>10 MeV) X-rays created by focusing kiloampere electron beam pulses to a tiny spot to produce bremsstrahlung radiation, a capability found at DARHT, FXR and the future Scorpius. Material science applications require radiation sources with flexible temporal and spectral characteristics (e.g. FELs) to probe substances at scales ranging from atomic to macro. Particle accelerator technology research offers a new generation of engineers and physicists opportunities to work in traditional (pulse line and discrete-component pulsed power technologies) 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 issues in beam stability, breakdown, surface plasmas, complex magnetic geometries and electromagnetics.
- Detectors, Diagnostics, Data Analysis and Data Processing: Novel and evolving experimental capabilities and new experimental methodologies open previously inaccessible parameter space in the laboratory, enabling entirely new families of experiments. New capabilities, in turn, require new diagnostic techniques, new recorders, new ways to handle, transmit and archive data, and modern analysis techniques. New sensors, detectors and recorders must provide increased sensitivity, improved resolutions, more speed, longer record lengths and faster data transfer. New analysis techniques include extended detector-system modeling that guides diagnostic development from concept to physics data delivery to the customer. Machine-learning is a growth area, especially as applied to image analysis and to the interpretation of large and diverse data sets from experiments and simulations. Diagnostic physicists and engineers have opportunities to explore the latest (and yet to be invented) detectors, including the imaging, optics, recording and data transfer and analysis techniques specifically those needed for advanced radiography.
Detailed understanding of the atomic physics of complex ions and of their interaction with radiation helps us grasp how complicated plasmas evolve in both stellar objects and laboratory experiments. 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 statistics can describe system populations, researchers write new opacity codes treating atomic physics with high precision and detail to model systems on exascale computers. Researchers use these codes to solve outstanding questions in astrophysics, such as radiation transport in the sun and the iron opacity problem. The latter refers to results 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 measured an iron opacity that can explain radiation transport in the sun but is completely outside the scope of the best models.
- Non-Local Thermodynamic Equilibrium: NLTE research solves rate equations between millions of atomic levels to study system populations and the resulting X-ray spectra. 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 inertial confinement fusion hohlraums. High-quality experimental data across a spectrum of plasma conditions informs models in radiation-hydrodynamic codes. Research is applying new analysis techniques involving genetic algorithms and other sophisticated methods to benchmark atomic physics codes to this data.
- Nuclear Astrophysics: Nuclear astrophysics focuses on the physics in systems ranging from the interiors of stars to the formation of shocks at the edges of forming galaxies. It encompasses a range of multi-physics topics, including radiation hydrodynamics, shock physics and nucleosynthesis, at scales from stars to laboratory systems.
- Laser-Matter Interactions: A detailed understanding of how high-energy laser pulses propagate in plasmas is essential to advance developments in inertial confinement fusion. Similarly, a detailed understanding of peta-watt laser-driven relativistic acceleration of charged particles; generation of neutrons, electrons and positrons; coherent and incoherent high-energy photon generation; and laser temporal compression and amplification schemes is important to many NNSA missions including new radiographic techniques.
- Dynamic Materials: Material properties in extreme conditions of pressure and temperature (0.1 to multi-Mbar and room temperature to many tens of eV) are critically important for numerous scientific applications, including shock physics, geoscience, astrophysics, inertial fusion and national security. Experiments and simulations involving phase transitions (solid-solid, solid-liquid), material structure, density, equation of state, constitutive and other properties are of interest.
Advancing our understanding of complex systems that span multiple time, space and spectral scales and engage multiple physics disciplines requires a balance of theoretical, computational and experimental efforts.
- Fluid Mechanics and Fluid Physics, including PIC/Fluid Hybrid Methods, Hydrodynamics, Instabilities and Shock Physics: Material motion and shock waves are generated when a laser, particle beam, or pulsed-power accelerator delivers large amounts of energy to matter in short timescales, making solid matter behave like a fluid. Hydrodynamic equations model the motion of this highly driven matter, including the wide array of fluid instabilities which govern its behavior. Researchers can use both simulations and experiments to understand how instabilities evolve, but their behavior is challenging to model or measure because it is often nonlinear. These systems also generate matter at numerous spatial and density scales, ranging from highly collisional, fluid-like behavior to collisionless, kinetic-like behavior. Researchers must develop modeling and simulation methods that treat both fluid and kinetic limits self-consistently within the same framework while self-consistently transitioning between the two conditions.
- Radiation and Radiation Magneto-Hydrodynamics: The discipline of radiation-magneto-hydrodynamics (RMHD) is essential to model a variety of multi-dimensional, strongly coupled and highly dynamical astrophysical, intense radiation source and fusion systems in high fidelity. These require self-consistent and fully coupled models of complex physical processes encompassing huge ranges of time and space. Research interests include developing and improving advanced numerical methods for RMHD and experimental studies and simulation of turbulence and instabilities.
To meet its primary objective of encouraging the training of scientists, the DOE NNSA LRGF program provides financial support to talented students who accompany their study and research with practical work experience at one or more of the following DOE NNSA facilities: Lawrence Livermore National Laboratory, Los Alamos National Laboratory, Sandia National Laboratories (New Mexico) or the Nevada National Security Site.