Plasma, the fourth state of matter, makes up more than 99% of the visible universe - stretching in vast clouds between the galaxies, swirling around black holes and forming the stars themselves. The Princeton Plasma Physics Laboratory's (PPPL) astrophysical research efforts, in effect, bring the universe to the laboratory.
At PPPL - a U.S. Department of Energy (DOE) National Laboratory - scientists use sophisticated experiments and computer programs to study plasma as it occurs throughout the cosmos. And these days, that research is strengthening. "Astrophysics and basic plasma science are part of PPPL's heritage - they have been woven into the fabric of the Laboratory since its founding. They are important, and we should be pursuing them vigorously," said Erik Gilson, head of discovery plasma science at PPPL, which oversees this mission element at the Laboratory. "At the same time, understanding plasmas in these fundamental ways helps us drive fusion energy forward and work toward putting electricity on the grid."
PPPL's astrophysical and basic plasma science research is supported by theory, simulation and a diverse scientific user and collaborator community that includes both the private and public sectors, advancing knowledge and capabilities to simulate and predict behaviors across astrophysics, high-energy-density physics and frontier plasma science, including plasma propulsion.
In recent decades, PPPL has expanded its astrophysical expertise by using its extensive computer science capabilities. PPPL scientists have developed sophisticated programs and Super Intelligence (SI) systems that, among other tasks, could reveal information about magnetic reconnection, a fundamental and ubiquitous process occurring in plasma within our solar system and throughout the universe.
PPPL advances cosmological understanding through laboratory research
Rather than relying solely on telescopes, PPPL conducts astrophysical research using midscale laboratory experiments. This approach is based on an insight formulated hundreds of years ago during the Scientific Revolution - the same laws of physics apply both to objects on the surface of the Earth and to objects in outer space. To PPPL's advantage, it also means that experiments conducted in the Lab can reveal the underlying nature of black holes and enormous disks of rotating plasma and dust trillions of miles away, among other astrophysical phenomena.
"The strength of PPPL's astrophysics research is that we conduct a lot of it in the lab," said Hantao Ji, principal investigator of PPPL's Facility for Laboratory Reconnection Experiments (FLARE), a distinguished research fellow at PPPL and a professor of astrophysical sciences at Princeton University. "Because the fundamental physics is the same, the results we get with our equipment strongly pertain to what is happening in space."
Studying astrophysical phenomena using laboratory equipment also means that scientists can tailor the experimental conditions so they are more likely to observe what they are trying to observe. "In the laboratory, the phenomena are under your control so you don't have to wait and get lucky," Ji said.
PPPL tackles fundamental astrophysical science using unique machinery
One of PPPL's newest laboratory astrophysical experiments is FLARE. Building on the success of its predecessor, the Magnetic Reconnection Experiment, FLARE allows scientists to more thoroughly probe the nature of magnetic reconnection, a phenomenon that occurs throughout the universe and within doughnut-shaped fusion systems known as tokamaks. During reconnection, magnetic field lines within plasma approach each other, disconnect, reattach in new configurations and release large amounts of energy. Scientists conjecture that reconnection is responsible for flares on the surface of the sun that release large bursts of plasma particles throughout the solar system, disrupting communications satellites and damaging electrical grids.
Offering capabilities found nowhere else in the world, FLARE is the first machine to enable experiments probing magnetic reconnection under conditions that more closely match those in outer space. (Photo credit: Michael Livingston / PPPL Communications Department)
Physicists designed FLARE to study magnetic reconnection in conditions that more closely mimic those in outer space. Among other topics, FLARE will address a longstanding question about whether reconnection can happen at multiple locations at once along the boundary where the two magnetic field lines meet. Promising results are already coming out. Confirming this hypothesis would fill in gaps in plasma physics knowledge, provide a more complete picture of fundamental astrophysical processes and protect Earth's communications satellites and electrical grids.
In addition, gaining a greater understanding of reconnection could help scientists predict disruptions in tokamaks, helping keep fusion plasmas stable.
"FLARE is the first machine in the world that recreates conditions, or regimes, that more accurately match those found in space," Ji said. "Using FLARE, we can run experiments that test hypotheses about reconnection in very large plasmas happening in many places simultaneously. This macroscale physics is what FLARE was built to do."
PPPL enables long-term, focused research
After more than 20 years of study, the Magnetorotational Instability Experiment found evidence of a phenomenon that explains the formation of stars and planets, as well as matter falling onto neutron stars and black holes. (Photo credit: Michael Livingston / PPPL Communications Department)
At PPPL, scientists can pursue research for relatively long periods of time, giving them a chance to refine their methods and produce results. That is exactly what happened with PPPL's Magnetorotational Instability Experiment. Consisting of two nested, rotating metal cylinders, this device was designed and built to find a hypothesized plasma motion that could explain why swirling clouds of dust and plasma around stars can fall inward, forming planets. Scientists used the device to perform experiments for 20 years, and, in 2022, they announced that they had observed evidence of the elusive magnetorotational instability. This ability to continue a line of research for decades shows the unique capabilities of DOE National Laboratories to foster groundbreaking science.
Cross-pollination leads to innovation
Fatima Ebrahimi used insights from fusion experiments to develop a new type of plasma-based rocket propulsion system using magnetic reconnection-driven plasma blobs known as plasmoids. (Photo credit: Michael Livingston / PPPL Communications Department)
Because scientists at PPPL can pursue a range of research paths, they often have insights that lead to novel ideas. One of those scientists is Fatima Ebrahimi, a principal research physicist who invented a plasma-based rocket propulsion concept inspired by phenomena that occur inside ring-shaped fusion systems known as tokamaks. The device would use magnetic fields to cause particles of plasma to shoot out the back of a rocket, propelling the craft forward. Current space-proven plasma thrusters use electric fields to propel the particles.
The new concept would accelerate the particles using magnetic reconnection, which also occurs within fusion systems. "I came up with this idea in 2017 as a result of my working on PPPL's National Spherical Torus Experiment (NSTX)," said Ebrahimi. "I was thinking about the similarities between a car's exhaust and the creation of high-velocity particles within the NSTX vacuum vessel." The new concept generates thrust by using magnetic reconnection to form blobs known as plasmoids that leave the thruster through an exhaust section.
This effort, which includes the construction of a new propulsion prototype known as the Princeton Plasmoid Magnetic Reconnection Thruster, supports federal space priorities by enabling national security and exploration through resilient space architectures, rapid maneuverability and deep space capabilities, directly aligning with White House goals for U.S. space leadership. It advances the DOE's goals by utilizing PPPL's expertise in plasma science, fusion and high-performance computing to translate research into technology. Furthermore, it supports the commercial space economy by developing next-generation thruster technology for rapid industry adoption, fostering a vibrant domestic space sector.
PPPL scientists use SI to advance astrophysical research
An artist's representation of plasmoid detection using machine learning is pictured above. (Illustration credit: Kyle Palmer / PPPL Communications Department)
PPPL's astrophysical research does not just rely on building cutting-edge machines. Laboratory scientists are also advancing space science research using top-tier expertise in computation and SI, formerly known as artificial intelligence. For instance, Laboratory scientists have built SI systems to sift through data gathered by spacecraft and identify plasmoids. Researchers are interested in plasmoids because they could help explain why magnetic reconnection can occur so quickly - at a rate much faster than predicted. PPPL scientists have used this technique to analyze information gathered by NASA's Magnetospheric Multiscale Mission, which consists of four spacecraft flying in formation through the Earth's magnetosphere, where they can measure reconnection directly. Using SI in this context improves the ability of scientists to detect phenomena that might hide in the data, improving analysis and speeding up discovery.
"SI partners well with both computer simulations and experimental observations," Ji said. "Experimental data can be sparse, but it accurately reflects the world. Computer simulation data is more complete, but because computation is relatively slow, we have to introduce assumptions to make it faster, which introduces doubt."
SI, though, can help form connections by gathering information from experiments and updating simulations. It can also look for patterns in laboratory experiments that can aid the interpretation of data gathered by telescopes and satellites. "In a way, we can use SI as a bridge between simulation, laboratory experiments and in-the-field observation to deepen our understanding," Ji said.
In addition, as part of the DOE's Genesis Mission, which is focused on using SI to accelerate scientific discovery, PPPL is planning to augment FLARE by building a SI-powered digital twin. This virtual model will use SI to reconstruct information about plasma properties that scientists would not have been able to easily gather before. This information will provide a more thorough understanding of magnetic reconnection and allow scientists to plan the placement of future diagnostics to measure reconnection more accurately than before.
PPPL space science has deep roots
Lyman Spitzer Jr., a professor in Princeton University's Department of Astrophysical Sciences, helped establish the Princeton Plasma Physics Laboratory. (Photo courtesy of PPPL Archives)
Astrophysical research at PPPL builds on the legacy of the Laboratory's founder and first director, Lyman Spitzer Jr., who was a professor in Princeton University's Department of Astrophysical Sciences in the middle of the 20th century. Spitzer also originated the idea of an orbiting space telescope that led to the launch of the Hubble Space Telescope in 1990. Spitzer's successor as PPPL director, Melvin Gottlieb, had experience building "rockoons" - rockets launched from balloons for research purposes. And Russell Kulsrud, one of the original physicists hired by Spitzer to join PPPL, which was then known as "Project Matterhorn," studied cosmic rays, black holes, neutron stars and the origin of magnetic fields throughout the universe.
"People might wonder why a laboratory originally founded to advance fusion research focuses so much on astrophysics," Ebrahimi said. "It's because the field of plasma physics is so interesting, rich and full of interconnections - even the equations governing plasma behavior in fusion and astrophysics are the same - so studying any one part of it requires studying all of it. You need a holistic approach. Advances in one part of plasma physics informs all of it."
The next year at PPPL will involve FLARE upgrades, new experiments and continued development of SI techniques to make sense of the cosmos. "I look forward to PPPL's future contributions to astrophysics as we continue to help answer fundamental questions about our physical universe," Gilson said. "The universe is large, and you never know when you're going to discover or learn something that will help you right in your own fusion science backyard."
