PSFC Students Receive Prestigious DOE Fellowships

Two graduate students at the Plasma Science and Fusion Center (PSFC) and the department of Nuclear Science and Engineering, Audrey DeVault and Bryan Foo, are recipients of highly competitive Department of Energy fellowships that support emerging leaders in high-energy density physics and nuclear science. The students’ work, developing novel forms of fusion fuel and deciphering the behavior of imploding plasmas, has exciting implications both for national security and for advancing fusion’s viability as a source of clean energy.

Audrey is one of six winners of the Department of Energy National Nuclear Security Administration Laboratory Residency Graduate Fellowship (DOE NNSA LRGF). Bryan is one of five winners of the Department of Energy National Nuclear Security Administration Stockpile Stewardship Graduate Fellowship (DOE NNSA SSGF).

It’s an incredible honor, says DeVault, who is pursuing her doctoral studies under the supervision of Dr. Maria Gatu Johnson, especially because the program enables her to pursue research at a national laboratory for two 12-week residencies. DeVault will conduct hers at Lawrence Livermore National Laboratory.

DeVault is studying laser-driven inertial confinement fusion (ICF), a method of producing incredibly hot, dense, fusion-triggering environments by directing laser energy at tiny fuel capsules. She got her start early on, as a highschooler. During the summer of 2018 she used neutron time-of-flight diagnostics —used to measure the energy of neutrons generated during laser-driven ICF experiments— to explore the symmetry of implosions at the University of Rochester’s Laboratory for Laser Energetics, home of the OMEGA laser facility.

After completing an undergraduate degree in physics at Caltech, where she conducted astrophysics and computer science research at NASA’s Jet Propulsion Laboratory, DeVault considered returning to her first love: laser-driven ICF.

While DeVault was researching and applying to graduate programs in the winter of 2022, the National Ignition Facility at Lawrence Livermore National Laboratory announced their groundbreaking achievement of fusion ignition, wherein more fusion energy was produced than was delivered to the target via laser energy. The excitement was palpable, DeVault remembers. It was time to make the switch from astrophysics back to fusion.

One side of DeVault’s research at the PSFC aims to evaluate the time evolution of nuclear implosions via neutron diagnostics. Doing so involves the challenging task of capturing both the energy and time of emission of released neutrons over the span of an implosion, which occurs on the order of 100 picoseconds, approximately one billionth of the time it takes for a human to blink. DeVault designs printed circuit boards and runs simulations to develop new time-resolving neutron diagnostics.

The other side of DeVault’s research, which will be the subject of her fellowship-funded residencies at Lawrence Livermore National Laboratory and the primary focus of her thesis, is the development and characterization of a novel target platform. DeVault is exploring the use of 3D-printed foams— sponge-like structures made up of pores the size of dust particles – for use in ICF fuel capsules.  Capsules with foam linings can be wetted with liquid fuel, making them faster and less expensive to manufacture than the solid (ice) fuel used in traditional ICF target capsules. The advantages of 3D printing: The foam is customizable, and unlike many other processes, delivers highly consistent outputs.

The goal in an implosion is to achieve smooth, symmetrical compression so that laser energy can be efficiently converted to pressure and heat. DeVault likens it to squeezing a ball of playdough tightly between your hands— if the compression isn’t even, the playdough will squeeze out of the gaps. In inertial confinement fusion experiments, asymmetries and nonuniformities during the compression of the target can lead to a loss of confinement and failure to produce the conditions required for fusion. It is therefore vital to understand how highly regular structures like 3D-printed foam pores may contribute to nonuniformities during compression.

DeVault’s current work aims to quantify the non-uniformity in the velocity of a shock front seeded by 3D printed wetted foams. Through an experiment conducted at the OMEGA laser facility in December of 2024, she and mentor Dr. Marius Millot aimed to measure the effect of target production variables like pore size, density, and thickness on the uniformity of the shock front. “The mechanical process of printing has so many variables,” DeVault says, “manufacturing constraints could have a massive impact on what we could actually implement as a target platform.”

DeVault expects her first summer as an LRGF fellow at Lawrence Livermore National Laboratory will focus on performing hydrodynamic simulations of wetted foams to understand their behavior, under the mentorship of Dr. Ryan Nora. The following summer will focus on manufacturing considerations under the mentorship of Dr. Xiaoxing Xia and further experimental characterization of the targets under the mentorship of Dr. Marius Millot. Through studying production, modelling, and experimental characterization, DeVault is taking a holistic approach to understanding this novel target platform.

Bryan Foo’s journey to inertial confinement fusion also started with his love of physics. In high school, growing up in Maryland, he loved math but soon realized he wanted to pursue a different subject. “The couple of pure math classes I took were great but I felt like I could never get invested in it if it wasn’t somehow used to describe the real world,” Foo says. Physics was the right fit. “To me physics was where I found a good intersection between having a lot of deep math but also it’s relevant to things in the real world, so it feels more tangible,” Foo adds.

During his undergraduate studies in physics at Princeton, Foo was drawn to plasma and high energy density physics. It was the field he decided to pursue in graduate school. The projects his advisor, Dr. Maria Gatu Johnson pitched seemed like a good mix of experiment and theory and Foo decided to jump in.

Foo’s current research involves investigating the kinetic effects in ICF implosions, which have applications in both fusion energy and stockpile stewardship. Studying ICF implosions helps understand the mechanics of an important pathway to fusion.

Most of the models used to simulate ICF implosions rely on the assumption that the plasma is in local thermal equilibrium at all times. But recent experiments have hinted that this assumption might be flawed. Scientists at the Lawrence Livermore National Laboratory, for example, found the spectrum of fusion neutrons that the plasma emits is sometimes atypical. It does not indicate a plasma in thermal equilibrium.

And that is a problem because if the assumption of plasma thermal equilibrium is flawed, the whole house of cards collapses. Inaccurate assumptions about the behavior of implosions affects reactivity predictions, which in turn affects the efficacy of fusion reactions.

Energy distributions can look different and overall reactivity might not be captured by existing models. Given that for more energy, you want better reactivity, “it’s important to study these things if we want to aim for higher reaction rates in the future.”  Foo says.

Foo wanted to find out what was going on to explain the departure from assumptions.

One proposed cause of the imbalance in the plasma’s thermal equilibrium involves fast ion beams accelerated to high energy by shocks. To explore this possibility, Foo is creating a diagnostically accessible mock-up of these ICF implosions, trying to tease out and measure some of these departures from thermal equilibrium and study how they might impact fusion reactivity. Using a diagnostic called Thomson scattering, he is trying to measure the velocity distributions of the ions appearing in the fusion reaction volume.

Foo is grateful for the perspective that conducting research at PSFC has given him. “This department has allowed me to learn more about social and economic aspects of nuclear energy too. Doing a physics undergrad didn’t expose me to these broader ideas so that has also been nice,” he says.

As part of his fellowship, Foo expects to continue this work at Los Alamos National Laboratory. “I’m most excited to use this opportunity to do more computational work with my collaborators at Los Alamos National Lab, especially in support of my experimental work,” he says. Part of the computational work would be to use the Implicit Fokker-Planck (iFP) code, which simulates kinetic effects and accounts for non-thermal activities. The computational aspect of Foo’s work also involves running simulations of collisionless shocks to evaluate non-thermal effects on electrons.

The fellowship will be an important step toward shaping Foo’s work and in helping him merge his love of math and physics into transformative research in fusion.

DeVault and Foo reflect the excellence of PSFC students and the center’s commitment to preparing the next generation of fusion leaders. With these prestigious awards, DeVault and Foo have an especially potent opportunity to realize the promise of fusion energy and move us one step closer to a zero carbon emissions future.