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Work heating up at PPPL during 50th year
Steven Schultz
By May, he had enough of a plan to secure $50,000 from the Atomic Energy Commission, and what was to become the Princeton Plasma Physics Laboratory was born. Now in its 50th year, the lab has indeed created a kind of star on earth, triggering and controlling thermonuclear fusion reactions at temperatures as great as 500 million degrees Celsius -- 25 times hotter than the core of the sun. In its early days, the lab was known as Project Matterhorn and its work was top secret. While Spitzer worked on fusion energy, John Wheeler, the Joseph Henry Professor of Physics Emeritus, was studying fusion for use in the hydrogen bomb. That work ended after the first H-bomb test of 1952, and by 1958 the lab's work was declassified. Looking aheadThe lab's colorful origins are reported in an upcoming history of the Forrestal Campus, written by James Merritt '66 and published by the University in honor of the campus' 50th anniversary. Attention at the lab, however, is focused on the future. "It is an exciting time in fusion science," said Robert Goldston, who is Spitzer's fourth successor as director of the lab, which is now funded by the U.S. Department of Energy and administered by the University. "We have generated the hottest ionized gasses, or plasmas, that have ever been made on earth, and we are understanding them at a depth that we never imagined possible." Fusion offers the possibility of an economical, environmentally benign and nearly limitless source of power, said Goldston. Its fuel consists of small amounts of so-called "heavy hydrogen," which can be extracted from seawater. Because it does not require the highly radioactive materials used in today's fission nuclear power plants, fusion would produce much less waste and risk of nuclear proliferation. Fusion is particularly safe because if the plasma touches the reactor vessel, it immediately becomes too cool to sustain the fusion reaction. "If you make a mistake you can annoy your shift supervisor, but you can't cause a disaster," said Goldston. So when might Spitzer's dream finally be realized, with fusion a major source of world energy? "It's certainly decades," said Goldston. "But how many depends, on the one hand, on our scientific results and, on the other, on how much funding the government puts behind this research. The science part is looking pretty good right now, and the new administration has included fusion in the National Energy Policy." Although decades may seem like a long time, Goldston noted that the nation's energy infrastructure turns over on a 30- to 50-year basis, meaning that now is the time to prepare the next generation of technology. In addition, the leading climate change studies suggest that by 2100 the world will need to derive at least half its power from non-fossil fuels. "That's a goal fusion science can deliver on," said Goldston. "Hopefully the political system can deliver on it as well." In many ways, the ideas Spitzer conceived on the ski slope remain central to fusion science today. Spitzer, who died in 1997, was an expert on interstellar plasmas, which are gasses heated so much that they lose all their electrons and become highly electrified. Matter needs to be in a plasma state to sustain a fusion reaction, but the idea of creating a container out of ordinary materials for such a reaction was ludicrous. Spitzer proposed containing plasmas within a magnetic force field. A careful arrangement of magnets would hold the plasma securely, preventing it from striking the solid walls of its confinement vessel. A series of test devices designed by Spitzer and others established a strong foundation for fusion science through the mid 1970s. Then, ready to attempt fusion at a larger scale, the lab built a large experiment called the Tokamak Fusion Test Reactor (TFTR), which began operating in 1982. The TFTR ushered in a remarkable period of experimental advances. It produced a record temperature of 500 million degrees Celsius, more than three times the amount needed for fusion, and produced 10 megawatts of fusion power, a world record. The extensive physics knowledge gained from TFTR, shut down in 1997, is now being applied in testing a smaller, more compact magnetic bottle that promises tighter control of plasma with considerably less hardware and energy requirements. The device, the National Spherical Torus Experiment (NSTX), has exceeded several key milestones a year or more ahead of schedule and has operated at 40 percent above its design specifications. Very fancy computationWhile the early history of the PPPL could be seen as a period of great experimental progress, the last decade has brought important advances in the theoretical understanding of plasma behavior. "If you think of it as a horse race between theory and experiment, in some ways theory caught up and has even taken the lead today," said Goldston. Theoretical advances have, for example, allowed scientists to fine tune the magnetic field to greatly reduce turbulence in the plasma. "This sense in which the theory is pulling us ahead is very exciting," said Goldston. Building on these insights as well as advances in modern supercomputing, the lab is proposing a second moderate-scale test device called a compact stellarator, a modern version of the very first design proposed by Spitzer. Unlike Spitzer, who used pencil and paper calculations to analyze three or four alternative designs, PPPL scientists used "very fancy computation" to look at 250,000 configurations, said Goldston. The resulting design has what appear to be rather odd curves in the vessel, but "it has remarkable underlying symmetries and should produce a plasma that is naturally steady in its operation." The device would be ready to run in 2006 and would go head-to-head with NSTX. "I view it as a friendly competition between these experiments," said Goldston. The winner might form the basis of the next large-scale experiment, which would be built in the space left behind by TFTR. In the immediate future, the PPPL is planning a 50th
anniversary symposium, which will take place at the lab on
Sept. 12-14. (Visit <http://www.pppl.gov> for
information and registration.) Goldston said the conference
will stress the connections between fusion energy science
and the many other areas of research that involve plasma
science. Such connections will be a key to the ultimate
success of fusion science, he said. |
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