Plasma can bend magnetic fields into unique shapes

Plasma, the fourth state of matter, holds many secrets yet to be uncovered, ranging from its behavior in space to its interaction with magnetic fields and potential applications on Earth.

One of its most intriguing mysteries is how plasma interacts with magnetic fields. This phenomenon is thought to occur both in the vast expanses between galaxies, shaping cosmic structures, and within fusion devices like tokamaks, where scientists strive to replicate the energy-generating processes of stars.

New research sheds light on the captivating and complex dance between plasma and magnetic fields, revealing insights that could revolutionize our knowledge of both astrophysical phenomena and practical fusion energy production.

Plasma and magnetic field interactions

Scientists at the Department of Energy’s Princeton Plasma Physics Laboratory (PPPL) have discovered an innovative way to capture the dynamic interaction between plasma and magnetic fields.

Protons, the subatomic particles that form the core of atoms, were used as a diagnostic tool to track and visualize these interactions with unprecedented detail.

“Observing magneto-Rayleigh Taylor instabilities arising from the interaction of plasma and magnetic fields had long been thought to occur but had never been directly observed until now,” said Sophia Malko, a PPPL staff research physicist and lead scientist on the project.

“This observation helps confirm that this instability occurs when expanding plasma meets magnetic fields. We didn’t know that our diagnostics would have that kind of precision. Our whole team is thrilled!”

Plasma bends magnetic fields

As the scientists conducted their measurements, they observed an unexpected and mesmerizing performance: the plasma, upon encountering the magnetic fields, exerted pressure that caused the fields to bend outward.

“When an expanding plasma pushes against a background magnetic field, it displaces the field out of its volume and forms a diamagnetic cavity. This expansion occurs until the equipartition of vacuum and magnetic pressure at the plasma’s outer boundary is reached, which determines the cavity’s maximum radius,” noted the researchers.

This interaction resulted in a dramatic and visually striking effect – a bubbling and frothing spectacle known as magneto-Rayleigh Taylor instabilities.

The instabilities manifested in the form of fascinating column and mushroom-like structures at the plasma boundaries, offering new insights into the fundamental behaviors that govern plasma dynamics in both natural and laboratory settings.

The mystery of plasma jets

When the plasma’s energy declined, the magnetic fields snapped back into their original positions, compressing the plasma into straight jets.

This is an important observation as these jets resemble those that stream from ultra-dense dead stars, known as black holes, extending for distances that are many times the size of a galaxy. The research suggests that these mysterious jets could be formed by similar compressing magnetic fields.

Magnetic fields: Architects of plasma jets

“These experiments show that magnetic fields are very important for the formation of plasma jets,” said Will Fox, a physicist at PPPL and the principal investigator of the research.

With their expertise in developing and building diagnostics, PPPL has been instrumental in the progress of measurement innovation in plasma physics.

The researchers used proton radiography, making an exciting tweak to the technique for this experiment to allow for extremely precise measurements.

The scientists shot a powerful laser on a small disk of plastic to create plasma and 20 lasers at a capsule containing fuel made of hydrogen and helium atoms variants to produce protons. The resulting fusion reactions led to a burst of protons and intense light, also known as X-rays.

Future of plasma research

The findings of this research have broadened the focus of PPPL to include research on high energy density (HED) plasma.

“HED plasma is an exciting area of growth for plasma physics,” said Fox. “The results show how the Laboratory can create advanced diagnostics to give us new insights into this type of plasma.”

The scientists at PPPL plan to work on future experiments to improve models of expanding plasma.

“Now that we have measured these instabilities very accurately, we have the information we need to improve our models and potentially simulate and understand astrophysical jets to a higher degree than before,” said Malko.

The study is published in the journal Physical Review Research.

Image Credit: Kyle Palmer / PPPL Communications Department

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