Magnetic field lines that wrap around the Earth protect our planet from cosmic rays. Researchers at the U.S. Department of Energy's (DOE) Princeton Plasma Physics Laboratory (PPPL) have now found that beams of fast-moving particles launched toward Earth from a satellite could help map the precise shape of the field. This mapping could provide insight into a region of the Earth's upper atmosphere known as the ionosphere, as well as the magnetosphere, the region of outer space affected by Earth's magnetic field, and help scientists predict how plasma belched from the sun can disrupt telecommunications satellites, cell phone calls, and global positioning systems.
"Understanding space weather - the behavior of hot, charged particles from the sun as they interact with the Earth's immediate environment - is critically important," said Andrew Powis, a graduate student in Princeton University's Department of Mechanical and Aerospace Engineering and lead author of a paper reporting the results in Frontiers in Astronomy and Space Sciences. "Developing a better fundamental understanding of how the magnetosphere operates is going to improve our ability to predict how it affects life on Earth."
Powis and PPPL physicist Igor Kaganovich, deputy head of the PPPL Theory Department, ran computer simulations to determine the feasibility of using a beam of electrons to measure the magnetic field. They sought to answer two questions that would help determine whether such a beam could be used as intended. First, would changing conditions in the magnetosphere affect where in the Earth's atmosphere the electron beam would strike? Second, would the electron beam stay focused enough to produce a strong-enough signal when hitting the atmosphere for ground-based instruments to detect?
"For these beams to teach us something about the magnetosphere, a change in the magnetosphere must cause a change in the electron beam's strike point," Powis said. "Our research has confirmed that this is the case."
Using codes on PPPL computers, the scientists also confirmed that the electron beam would remain focused enough to create an observable signal, acting in effect as an aurora. "If you have all these particles spreading out and impacting over thousands of square kilometers," said Powis, "you wouldn't be able to detect their individual signatures above the background noise, or even above the natural aurora itself."
Powis hopes that a satellite with the electron beam technology will fly in the near future. "There is uncertainty about magnetospheric storms and how they affect telecommunications satellites and the electric grid. This tool would be able to settle some of the uncertainty."
Powis and Kaganovich would next like to model how the electron beam interacts with the plasma - the state of matter composed of free-standing electrons and atomic nuclei - in the Earth's ionosphere and how the beamed electrons would affect one another. Initial calculations suggest that these interactions should not significantly affect the spreading of the beam, "but we want to be rigorous," Powis said.
These findings were the result of collaborations with a wide range of researchers, including undergraduates in the DOE's Science Undergraduate Laboratory Internships (SULI) program, high school students in PPPL's science education program, and graduate students enrolled in other departments at Princeton University. "It was great seeing the development of the next generation of plasma physicists," said Kaganovich.
The research was part of a larger project that included the National Aeronautics and Space Administration (NASA) and the DOE's Los Alamos National Laboratory. PPPL's role was to use both pen-and-paper theoretical calculations and computer simulations to study the behavior of the electron beam.
Support for this work came from the DOE, the National Science Foundation, and PPPL's Laboratory-Directed Research and Development funds. Other members of the research team physicist Peter Porazik, now at Lawrence Livermore National Laboratory; visiting research students Michael Greklek-McKeon of the California Institute of Technology, David Shaw of the University of Notre Dame, and then-high-school-student Kailas Amin, now of Harvard University; Andrews University engineering professor Jay Johnson; and SRI International scientist Ennio Sanchez.
