Scientists have gained new insights into how plasma interacts with magnetic fields, which might help explain the origins of massive plasma jets that travel between stars.
Plasma, the electrically charged fourth state of matter, frequently interacts with strong magnetic fields, whether in the space between galaxies or in the doughnut-shaped devices used for nuclear fusion called tokamaks. This interaction alters plasma’s shape and behavior. A novel measurement technique utilizing protons—subatomic particles at the core of atoms—has revealed details of this behavior for the first time, offering potential explanations for the vast plasma jets that extend across star systems.
Researchers from the U.S. Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL) have captured vivid images of a magnetic field expanding outward due to pressure from expanding plasma. As this plasma exerted force on the magnetic field, bubbling and frothing known as magneto-Rayleigh Taylor instabilities emerged along their edges, forming structures that looked like columns and mushrooms.
As the energy within the plasma decreased, the magnetic field lines returned to their initial positions, causing the plasma to compress into a streamlined form that resembles the jets produced by black holes—ultra-dense remnants of dead stars that can extend vast distances, often many times the size of a galaxy. These findings suggest that the same compressing magnetic fields identified in this study could also be responsible for creating these cosmic jets, which have remained a mystery.
“When we conducted the experiment and analyzed our data, we realized we had discovered something significant,” stated Sophia Malko, a staff research physicist at PPPL and lead author of the study. “While the existence of magneto-Rayleigh Taylor instabilities was long believed to occur during the interaction of plasma and magnetic fields, it had never been directly observed until now. This confirmation of the instability occurring when expanding plasma meets magnetic fields was unexpected, and our entire team is highly excited about the precision of our diagnostics!”
“Our experiments clearly show that magnetic fields play a critical role in the formation of plasma jets,” noted Will Fox, a PPPL research physicist and principal investigator of the findings reported in Physical Review Research. “This newfound understanding gives us a theoretical framework to explore giant astrophysical jets and learn more about black holes.”
PPPL is renowned for its capability in developing diagnostic tools that measure plasma properties such as density and temperature under various conditions. This accomplishment adds to a series of recent advancements showcasing the lab’s progress in measurement innovation in plasma physics.
Utilizing an innovative technique for remarkable detail
The research team enhanced a measurement technique called proton radiography by creating a new variation specifically for this experiment aimed at achieving extremely precise measurements. To generate plasma, they directed a powerful laser at a small disk made of plastic. To produce protons, they employed 20 lasers on a fuel capsule containing different hydrogen and helium isotopes. The resultant fusion reactions led to the release of both protons and a powerful burst of X-rays.
Additionally, the team placed a mesh with tiny holes adjacent to the fuel capsule. As the protons passed through the mesh, they formed separate beams that were then altered due to the surrounding magnetic fields. By comparing the distorted image of the mesh to an undistorted image from the X-rays, the researchers gained insights into how the expanding plasma influenced the behavior of the magnetic fields, resulting in swirling instabilities at the edges.
“Our experiment was unique because we could observe the magnetic field changing in real-time,” Fox explained. “We directly witnessed how the field gets pushed outward in a kind of tug-of-war with the plasma.”
Diversifying the research agenda
The results exemplify the PPPL’s expanding research agenda that includes high-energy-density (HED) plasma studies. Unlike those used in standard fusion experiments, these plasmas, similar to those produced in the experiment’s fuel capsule, have higher temperatures and densities. “Research on HED plasma is a thrilling area of growth within plasma physics,” Fox commented. “This work is part of PPPL’s commitment to advance this field. The findings indicate our lab’s ability to develop sophisticated diagnostics that provide new insights into this plasma type, which can be utilized for laser fusion technologies and methods employing HED plasma to produce radiation for microelectronics fabrication.”
According to Fox, “PPPL’s extensive expertise in magnetized plasmas can significantly contribute to the realm of laser-generated HED plasmas.”
“HED science is intricate, intriguing, and vital to comprehending a wide variety of phenomena,” stated Laura Berzak Hopkins, PPPL’s associate laboratory director for strategy and partnerships and deputy chief research officer. “Achieving these conditions in a controlled manner and creating advanced diagnostics for meticulous measurements presents notable challenges. These thrilling results highlight the effectiveness of combining PPPL’s ample technical knowledge with pioneering methodologies.”
More experiments and improved simulations
The research team plans to conduct further experiments to enhance models related to expanding plasma behavior. “Scientists have often assumed that density and magnetism vary directly in these scenarios, but that may not be the case,” Malko noted.
“Having accurately measured these instabilities, we can refine our models and potentially simulate and gain a deeper understanding of astrophysical jets,” Malko added. “It’s fascinating how we can replicate phenomena that typically exist in outer space within a laboratory setting.”
The collaboration involved researchers from the University of California-Los Angeles, Sorbonne University, Princeton University, and the University of Michigan. The research received funding from the DOE’s Laboratory-Directed Research and Development program, under contract number DE-AC02-09CH11466. The experiment utilized the University of Rochester’s Omega Laser Facility with support from DOE/National Nuclear Security Administration contract number DE-NA0003856.
