Raspberry Simpson

Raspberry Simpson, a Lawrence Postdoctoral Fellow at Lawrence Livermore National Laboratory (LLNL), stands at the cutting edge of experimental physics, driving advancements in laser-driven particle acceleration and transformative applications. As part of the Short Pulse Laser Science and Applications Team led by Dr. Matthew Hill, Simpson’s research is shaping the future of inertial fusion energy, high-energy-density physics, and national security through pioneering experimental methods and machine learning tools.

Path to Livermore

Simpson’s journey to LLNL reflects her lifelong curiosity and a relentless pursuit of scientific discovery. Raised in New York, Simpson enjoyed frequent visits to the Hayden Planetarium and the Natural History Museum with her mother, whose resourcefulness and intellectual rigor inspired an early love of learning. “She always instilled in me a desire to ask questions and never stop until you find the answer,” Simpson recalls. Despite limited resources, Simpson’s mother ensured access to every educational opportunity the city could offer, nurturing a passion for science that would define Simpson’s career.

At just 15, Simpson enrolled at Bard College at Simon’s Rock, a small liberal arts institution known for its early college program, before transferring to Columbia University to earn a B.S. in Applied Physics. During college, a pivotal internship at Los Alamos National Laboratory introduced Simpson to the unique environment of the National Laboratory complex. “I loved the environment so much that I spent two years after college at LANL working in inertial confinement fusion diagnostic research,” said Simpson.

Inspired by the potential of fusion energy and the collaborative spirit of the National Laboratories, Simpson pursued a Ph.D. in nuclear engineering at MIT. Through the NNSA Laboratory Residency Graduate Fellowship, Simpson completed much of her graduate work with Dr. Tammy Ma at LLNL, whose blend of compassionate mentorship and technical excellence continues to serve as a model. “Tammy is always an inspiration to me in how she is able to combine compassionate mentorship and a strong motivation for technical excellence,” says Simpson.

Mission-Driven Research 

Simpson’s work at LLNL explores the science of laser-driven particle acceleration—a field with profound implications for energy, national security, and fundamental physics. Collaborating with the Short Pulse Laser Science & Applications Team, Simpson investigates how high-intensity lasers interact with thin solid foils to create plasmas with exceptionally strong electric fields. These fields are capable of pulling ions from the foil’s surface and accelerating them to high energies, a process known as Target Normal Sheath Acceleration (TNSA) first explored at LLNL.

One of Simpson’s key projects focuses on the alternative inertial fusion energy (IFE) approach known as ion fast ignition (IFI). IFI represents a promising pathway to achieving the high gain and high-repetition rate fusion concepts necessary for future energy solutions. By separating the compression and heating phases in inertial confinement fusion, IFI seeks to reduce driver energy and symmetry requirements compared to traditional central hot spot ignition schemes. “The fast ignition scheme was actually first invented by Max Tabak at LLNL,” Simpson notes.

In IFI, a spherical capsule of deuterium-tritium fuel is compressed to high densities using a long-pulse laser drive, then heated to fusion-relevant temperatures by short-pulse, laser-generated ions. Simpson’s research explores this scheme across several world-class laser facilities, including the OMEGA facility at the Laboratory for Laser Energetics and the National Ignition Facility. These experiments not only advance the science of fusion energy but apply world-class science and technology to national security.

“Laser-driven sources are an important toolkit in our work since they can be used to both create extreme states of matter at high temperatures and densities, but also probe and measure states of matter relevant to stockpile stewardship, the interior of planets, and inertial confinement fusion,” Simpson explains. 

The physics of laser-driven particle acceleration extends far beyond the confines of the Laboratory, with applications that touch many aspects of modern life and technology. “The physics of laser-driven sources have very large application spaces and thus large impacts on all of us,” Simpson observes. These sources can probe and create extreme states of matter, play a key role in fusion energy schemes, and are integral to technologies like laser-driven EUV sources used in semiconductor chip production. Some research groups are even exploring the potential of laser-driven sources for proton cancer therapy, opening new avenues for medical innovation.

Innovation Through Collaboration

Simpson’s motivation is deeply tied to the collaborative culture and ambitious scientific mission of LLNL. “Being able to make a small impact to that mission feels very exciting, and it’s also a privilege. I feel very lucky to be able to work on some of the biggest scientific facilities with some of the most hardworking and talented people on the planet to move some of these big questions forward, like energy and nuclear security.”

Simpson also emphasizes the importance of mentorship, both as a recipient and as a mentor to the next generation of scientists and engineers. “I feel like I’ve benefitted from a lot of excellent mentorship at the Lab, and it has been fun for me to give that back and learn to be a mentor,” Simpson says. 

Vision for the Future

Simpson’s work exemplifies the spirit of curiosity, collaboration, and technical excellence that defines LLNL. By developing new experimental and machine learning tools to optimize laser-driven secondary particle sources, Simpson is not only advancing the frontiers of physics but also contributing to the Lab’s mission of national security and scientific leadership. The potential for fusion energy, advanced diagnostics, and new applications in medicine and technology makes this research both timely and transformative.

Looking ahead, Simpson envisions a future where LLNL continues to lead in fusion energy and laser-driven particle acceleration, supported by robust interdisciplinary teams and state-of-the-art facilities. The realization of an inertial fusion energy demonstration facility redefines the possibilities of energy generation and scientific discovery. 

“In fusion energy, I think LLNL is a clear leader in this field, and being able to realize an inertial fusion energy demonstration facility here at Livermore Lab would be very exciting!” Simpson says. Simpson is confident that LLNL is one of the few places capable of producing this kind of scientific moonshot. “There are so many people already working on what this might look like, especially Tammy Ma. It would be such a complex facility to work through the components of, but I believe a place like LLNL is one of the few places that can produce that type of moonshot. I would feel very lucky to see that one day here!”

In a rapidly evolving geopolitical environment, the need for more people working across disciplines is even more important. “As the problems that the Laboratory is solving become more and more complex, we always need more people working interdisciplinary and the next generation facilities that can push us into new frontiers of science.”