Researchers Look to Harness the Power of the Stars
The Record, Volume 30, Issue 6, p. 3, 12/17/2004
Star Trek aficionados and physics buffs know better, but many of us are familiar with only three states of matter: solids, liquids and gases. Any trekkie, however, can tell you about a fourth state of matter—plasma, the state of high-temperature matter found in stars. Now Columbia University students, researchers and their MIT counterparts have begun a novel experiment that will test whether the plasma created within a new type of reactor might lead to a fusion energy source. Fusion is a possible energy source for the future that is free of green-house gas emission and does not contribute to global warming.
The experiment, known as the levitated dipole experiment (LDX), is the first of its kind and confines high-temperature ionized gas with magnetic force fields generated by a half-ton superconducting ring. When heated to a high tempera- ture—200 million degrees at the hottest point in the LDX—gas changes its behav- ior and properties and becomes plasma: the ionized state of matter of nearly the entire visible universe.
Results of the first round of LDX tests were presented at a meeting of the American Physical Society the week of Nov. 15. More than 100 plasma discharges were created within the new device, each lasting from 5 to 10 seconds. X-ray spectroscopy and visible photography recorded spectacular images of the plasma, capturing the dynamics of how this type of matter behaves within the confines of magnetic force fields.
Going forward, scientists will use LDX to study plasma and investigate whether someday it may be used to produce fusion energy on Earth. Fusion is the energy source of stars, including the sun. Inside stars—and inside the LDX—under high temperature and high pressure, light-weight elements such as hydrogen are fused together to make heavier elements such as helium. This process releases large amounts of energy. Fusion energy is advantageous because its fuel, hydrogen, is nearly limitless; the hydrogen fuel for fusion energy is found in water. Fusion energy is also clean and would not contribute to global warming as does the burning of fossil fuels.
Magnetic fields are needed to confine and control the plasma in which fusion occurs. The primary confinement fields are created by a powerful superconducting ring about the size of a truck tire and weighing more than half a ton that will ultimately be levitated within a large vacuum chamber. A second superconducting magnet located above the vacuum chamber provides the force necessary to support the weight of the floating coil. The resulting force field resembles the fields of the magnetized planets, such as Earth and Jupiter. Using satellites, scientists have observed how these fields confine plasma at hundreds of millions of degrees.
The LDX research team is led by Michael Mauel, a professor of applied physics at Columbia University, and Jay Kesner, senior scientist at MIT’s Plasma Science and Fusion Center (PSFC). Mauel and Kesner’s colleagues on the experiment include Eugenio Ortiz, a CU graduate student, and Columbia scientists Darren Garnier and Alex Hansen, as well as Rick Lations, Phil Michael, Joseph Minervini, Don Strahan and Alex Zhukovsky of the PSFC.
Because the shape of the force field determines the properties of the confined plasma, several different fusion research experiments are under way throughout the world, including a second experiment at MIT, the Alcator C- Mod, and the HBT-EP experiment at Columbia. The work is sponsored by the United States Department of Energy, Office of Fusion Energy Sciences.