Among the most puzzling phenomena in the universe, mysterious fast cosmic radio bursts release as much energy in one second as the sun pours out in a year. Now PPPL researchers and the SLAC National Accelerator Laboratory have simulated a cost-effective experiment to produce the early stages of this process in a way once thought to be impossible with existing technology. 

Creating the extraordinary bursts in space are celestial bodies such as collapsed stars called magnetars (magnet + star) that are enclosed in extreme magnetic fields. These fields are so strong that they turn the vacuum in space into an exotic plasma composed of matter and antimatter in the form of pairs of negatively charged electrons and positively charged positrons, according to quantum electrodynamic (QED) theory. Emissions from these pairs are believed to be responsible for the powerful fast radio bursts.  

“Our laboratory simulation is a small-scale analog of a magnetar environment,” said physicist Kenan Qu of the Princeton Department of Astrophysical Sciences. “This allows us to analyze QED pair plasmas.”

Qu is the first author of a study showcased in Physics of Plasmas as a science highlight and the first author of a paper in Physical Review Letters that the present paper expands on. 

“Rather than simulating a strong magnetic field, we use a strong laser,” Qu said. “It converts energy into pair plasma through what are called QED cascades. The pair plasma then shifts the laser pulse to a higher frequency. The exciting result demonstrates the prospects for creating and observing QED pair plasma in laboratories and enabling experiments to verify theories about fast radio bursts.” 

No lasers are strong enough to achieve this today and building them could cost billions of dollars, Qu added. “Our approach strongly supports using an electron beam accelerator and a moderately strong laser to achieve QED pair plasma. The implication of our study is that supporting this approach could save a lot of money.” 

PPPL researchers have gained insight into a fundamental process called magnetic reconnection found throughout the universe. They discovered that the magnetic fields threading through plasma, the charged state of matter composed of free electrons and atomic nuclei, can affect the dynamic coming together and snapping apart of reconnection. This insight could help predict the occurrence of coronal mass ejections — enormous burps of plasma that reconnection releases from the sun, which could threaten communication satellites and electrical grids on Earth.

The scientists focused on the role of guide fields, magnetic fields threading through plasma blobs, or chunks, known as plasmoids. These fields add rigidity to the blobs and help determine how much reconnection occurs. The fields also occur in donut-shaped tokamaks, the most widely used type of fusion facility that confines plasma in the effort to harness fusion, the power that drives the sun and stars.

The process resembles the parallel computing that occurs in smart phones and high-powered computers that model the weather. Many processors are calculating simultaneously and making the overall calculation rate quicker. Similarly, plasmoids speed up the overall rate of reconnection by making it occur in many places at once.

“Understanding how guide magnetic fields affect plasmoids could give us a better idea of what affects magnetic reconnection on the sun and stars, and throughout the cosmos,” said Stephen Majeski, lead author of a paper reporting the results in Physics of Plasmas and a graduate student in Princeton University’s Program in Plasma Physics. “Guide fields are a knob we can turn up to reveal new information.”

The finding marks new territory for plasmoid reconnection research, said Hantao Ji, professor of astrophysical sciences at Princeton University and distinguished research fellow at PPPL. Ji also who helps manage PPPL’s Magnetic Reconnection Experiment (MRX) that studies reconnection. “Majeski has added to our knowledge about guide fields to make progress toward understanding large-scale reconnection based on plasmoids. Nobody has looked at guide fields in this way before.”

Researchers have uncovered a previously hidden heating process that helps explain how the atmosphere that surrounds the sun called the “solar corona” can be vastly hotter than the solar surface that emits it.

The discovery at the DOE’s PPPL could improve tackling astrophysical puzzles ranging from star formation to the ability to predict eruptive space weather that can disrupt cell phone service and black out power grids on Earth. Understanding the heating process also has implications for fusion research.

“Our direct numerical simulation is the first to provide clear identification of this heating mechanism in 3D space,” said Chuanfei Dong, a physicist at PPPL who unmasked the process by conducting 200 million hours of computer time for the world’s largest simulation of its kind. The finding is published in the journal Science Advances.

The hidden ingredient is magnetic reconnection, a universal process that separates and violently reconnects magnetic fields in plasma, the soup of electrons and atomic nuclei that forms the solar atmosphere and fuels fusion reactions. Dong’s simulation revealed how rapid reconnection of the magnetic field lines turns the large-scale turbulent energy into small-scale internal energy. This converts the large-scale turbulence to small-scale turbulence that superheats the corona.

“Think of putting cream in coffee,” Dong said. “The drops of cream soon become whorls and slender curls. Similarly, magnetic fields form thin sheets of electric current that break up due to magnetic reconnection. This facilitates the energy cascade from large scale to small scale, making the process more efficient in the turbulent solar corona than previously thought.”

It does this by breaking and rejoining the magnetic field lines — the faster the better — to generate chains of small, twisted lines called plasmoids. This changes the understanding of the turbulent energy cascade that has been widely accepted for more than half a century, said the authors of the paper. The new finding ties the energy transfer rate to how fast the plasmoids grow, enhancing the transfer of energy from large to small scales and strongly heating the corona at these scales.

The impact of this finding in astrophysical systems across a range of scales can be explored with current and future spacecraft and telescopes, said the authors. And unpacking the energy transfer process across scales will be crucial to solving key cosmic mysteries.

The information age created over some 60 years has given the world the internet, smart phones and lightning-fast computers. Making this possible has been the doubling of the number of transistors that can be packed onto a computer chip roughly every two years, giving rise to billions of atomic-scale transistors that now fit on a fingernail-sized chip. Such “atomic scale” lengths are so tiny that individual atoms can be seen and counted in them.

With this doubling now approaching a limit, the DOE’s PPPL has joined industry efforts to extend the process and develop new ways to produce ever-more capable and cost-effective chips. Laboratory scientists have now accurately predicted through modeling a key step in atomic-scale chip fabrication in the first PPPL study under a Cooperative Research and Development Agreement (CRADA) with Lam Research Corp., a world-wide supplier of chip-making equipment.

“This would be one little piece in the whole process,” said David Graves, associate laboratory director for low-temperature plasma surface interactions, a professor in the Princeton Department of Chemical and Biological Engineering and co-author of a paper that outlines the findings in the Journal of Vacuum Science & Technology B. Insights gained through modeling, he said, “can lead to all sorts of good things, and that’s why this effort at the Lab has got some promise.”

The PPPL scientists modeled what is called “atomic-layer etching” (ALE), an increasingly critical fabrication step that aims to remove single atomic layers from a surface at a time. This process can be used to etch complex three-dimensional structures with critical dimensions that are thousands of times thinner than a human hair into a film on a silicon wafer.

“The simulations basically agreed with experiments as a first step and could lead to improved understanding of the use of ALE for atomic-scale etching,” said Joseph Vella, a postdoctoral fellow at PPPL and lead author of the paper. “Improved understanding will enable PPPL to investigate such things as the extent of surface damage and the degree of roughness developed during ALE,” he said.

Going forward, “the semiconductor industry is contemplating a major expansion in the materials and the types of devices to be used,” said Graves, “and this expansion must be processed with atomic-scale precision. The U.S. goal is to lead the world in using science to tackle important industrial problems, and our work is part of that.”