In a small, tungsten-lined chamber in a Swarthmore College laboratory, physicist Michael Brown and a team of undergraduates are recreating conditions found on the surface of the sun -- including temperatures near one million degrees -- to give science its first up-close look at solar flares and the heating of the sun's enigmatic corona.
Brown, who last year won the Department of Energy Junior Investigator Award, says the research has three purposes: to study the complex and little-understood physics of solar flares and the corona; to advance the development of nuclear fusion technology; and to introduce undergraduate science students to plasma physics, the study of hot, ionized gases like those found on the sun.
Solar flares are huge loops of flaming, ionized gas that reach above the sun's surface to heights more than ten times the Earth's diameter. During particularly intense bursts, they generate powerful magnetic fields and energetic particles that can disrupt satellite communications on Earth. Brown notes that little is known about the cause of the flares and the process by which they heat the corona, the atmosphere over the sun, to temperatures 1,000 times greater than those on the solar surface.
"In the corona and solar flares, we have two very old physics problems that haven't been solved," says Brown, a former Caltech senior research fellow who chose Swarthmore from an array of job offers for the chance to work closely with undergraduates. "I realized that these problems could be addressed with undergraduates at Swarthmore in a way that would advance both science and the training of the next generation of scientists."
Scientists have puzzled for years over the "dynamo problem" -- the process by which solar flares are formed -- and the extremely high temperature of the corona. Says Brown: "We think the magnetic fields in the flares are generated by a 'dynamo' in the core of the sun that converts the spinning motion of the sun into electric current and magnetic fields. We think the corona is heated by the self-destruction of the flares, which converts their magnetic energy into x-rays and heat."
The Swarthmore research is attempting to illuminate the phenomena in two ways. To explore the dynamo problem, Brown and his students create and analyze a spinning sphere of liquid sodium, looking at the conversion of spinning kinetic energy to magnetic energy. To study the corona heating problem, meanwhile, they merge two magnetized plasma rings and analyze the conversion of the magnetic energy into x-rays and heat.
Brown and his students are conducting the research with a specially designed cylindrical chamber called a "spheromak," which the team built with start-up money from the College and now operates with grants from the National Science Foundation and the Department of Energy. The experiment works like this: A plasma "gun" powered by high electrical voltage and current shoots a miniature solar flare into the chamber. Temperatures as high as those found on the sun would normally melt any substance on earth, but the experimental burst lasts for just a few hundred-millionths of a second. That's enough time for dozens of tiny probes to observe the phenomenon and send data to a computer in a nearby control room, where the complex process is modeled and analyzed. Of particular interest to the researchers is the strength and motion of the magnetic field created by the bursts.
"The flares we create have the same twisting shape and the same temperature, material, density, and magnetic field as those on the sun," Brown says. "Except for the size, if you looked at ours and then went to the surface of the sun, you couldn't tell the difference."
The research has the attention and funding support of the Department of Energy, which believes the work could lead science closer to unlocking the potential of nuclear fusion to provide a clean and limitless power source.
Three to five Swarthmore students, many of them enrolled in the College's acclaimed honors program, join Brown full-time in the laboratory each summer to contribute to the research while furthering their own education. Students also participate during the academic year. The student-researchers present their work at national conferences, and several have co-authored papers published in top scientific journals. One student participating in the project, Cameron Geddes, last year won the Apker Award of the American Physical Society for the top undergraduate physics thesis in the country.
Swarthmore, located outside of Philadelphia, is a highly selective liberal arts college with enrollment of approximately 1,370.
Note: A more detailed description of the research is available at http://laser.swarthmore.edu/html/research/SSX/index.html.
Materials provided by Swarthmore College. Note: Content may be edited for style and length.
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