![]() This issue... 11 Physics Questions for the New Century Astrophysicists Explore Supernovae Long-Life Rechargeable Batteries
This issue...
11 Physics Questions for the New Century
Astrophysicists Explore Supernovae
Long-Life Rechargeable Batteries
This issue...
11 Physics Questions for the New Century
Astrophysicists Explore Supernovae
Long-Life Rechargeable Batteries
This issue...
11 Physics Questions for the New Century
Astrophysicists Explore Supernovae
|
View from the InsideRob GoldstonPrinceton Plasma Physics LaboratoryWhat's Up With Fusion?by Nona Shepard
In the past five years, fusion scientists have learned how to calm the turbulence that causes much loss of heat energy from plasmasthe hot ionized gases that serve as the fuel for fusion energy production. When Rob Goldston, became Director of DOE's PPPL in 1997, there were only theoretical hints of the ultimately successful technique. ES News interviewed Professor Goldston to learn how those hints became a scientific breakthrough, and what this and other advances in plasma science mean for the future of magnetic fusion research.ES News: Professor Goldston, what's been going on at PPPL to make you so enthusiastic about fusion science? Goldston: As you know, one of the big issues in fusion has been how to hold plasmas stably inside a toroidal (donut-shaped) container where the temperature can be as high as 500 million degrees centigrade. Over the short span of five years, a major leap has been made. It's an important breakthrough. So I like to explain it to people. ES News: Please, tell us about it. Goldston: In the mid 90's, we began to understand more deeply how to control the turbulence that causes plasmas to lose heat. A relatively simple theory hinted that if we reconfigured the magnetic field to make the electric current that flows in the plasma flow toward the outside, instead of flowing close to the center, the plasma would be less turbulent and heat retention would be improved. These ideas were confirmed dramatically in specially tailored experiments. Since then, we have also discovered that if the plasma has a sheared flowif the flow in one part of the plasma has a different flow speed than in another part of the plasmathen swirls of turbulence that try to build up are torn apart. As the plasma flows, it just shears these swirls apart, which also reduces heat losses. There is now nice agreement between the theoretical understanding of that shearing effect and a wide range of experimental observations. ES News: Did advances in computing contribute to the development of the latest theories on plasma turbulence? Goldston: Absolutely. Simulations made possible by advances in parallel processing allow us to realistically visualize plasma behavior predicted by our advanced models. The computers we use, particularly at the National Energy Research Supercomputer Center (NERSC) at Berkeley, keep getting faster and more powerful, allowing us to simulate full-scale experiments. We are striving to add more detail to these full-scale simulations. This is very exciting. But desk-top monitors have not kept pace in terms of their resolution capability. To solve this problem, PPPL has constructed a Visualization Wall that can project images with a resolution more than three and a half times better than high-resolution TV. Ten clustered computers work together and nine projectors beam pixelated images onto the Wall. Nine standard displays are tiled together to make one display with superior clarity. The PPPL Visualization Wall is allowing our theoreticians to see fine-scale structure in the output from the supercomputers, including simulations of plasma turbulence. PPPL is the first U.S. fusion facility to have such a wall. Many of the ideas and technologies for this display came from work done on the main campus of Princeton University. ES News: Has the fusion program's strong focus on fundamental science enabled breakthroughs like this one?
Goldston: Yes, our increased knowledge of the underlying fundamental plasma science has made us more confident about moving forward with new fusion experiments such as the National Spherical Torus Experiment (NSTX) at PPPL. In fact, our new theoretical understanding suggests that shear flow will have a really strong effect in a spherical torus configuration. In this geometry, the plasma is fattershaped more like a cored apple than a donut. The center hole contains only a very slender column. The fatter plasmas also allow higher beta valuesthe ratio of plasma pressure to magnetic field pressure. Since fusion power production is roughly proportional to the square of the plasma pressure, a higher beta means that substantially more fusion power output is achieved with a given magnetic field strength. This may lead to smaller, more economical fusion systems.
NSTX is also taking advantage of another major discovery. Many years ago, theoreticians had predicted that the plasma current could be self-sustaining. This phenomenon, known as bootstrap current, was observed for the first time during experiments on the Tokamak Fusion Test Reactor at Princeton in the mid 1980s. NSTX will use this bootstrap effect to sustain the plasma current, and we are investigating bootstrap and other techniques to start the current without using a transformera gadget that takes up space in the center hole. If we can eliminate this transformer, we can make the hole smaller and the plasma chubbier. Then the pressure will go up and so will the sheared flow. ES News: How is NSTX doing? Goldston: Exceptionally well. It began operation in February 1999. By December 1999, it had produced its design plasma current of 1 million amperes, nine months ahead of schedule, and had produced all of the plasma shapes needed for its experiments. Since then it has produced a plasma current of 1.4 million amperes, 40% above its goal. In September 2000, NSTX's neutral-beam injection (NBI) system began operating ahead of schedule. The use of NBI plasma heating coupled with exceptionally good plasma confinement has resulted in a toroidal beta of 25%. Toroidal beta is the ratio of plasma pressure to magnetic field pressure in the long direction around the spherical torus. For reference, the highest toroidal beta produced in a tokamak stands at about 13%. NSTX's toriodal beta accomplishment was achieved more than a year ahead of schedule, with much less plasma heating power than expected. This bodes well for the prospect that NSTX eventually will have adequate heating power to test the theoretically predicted toriodal beta values in the range of 40% for a spherical torus. ES News: Besides the spherical torus concept, what other ideas are currently being studied? Goldston: There's a whole portfolio. The idea is to have a breadth of focus that allows new ideas to get tried out and to benefit each other from the deeper understanding that comes from the research. There are a number of small-scale experiments at universities around the country and at the national laboratories. In addition to NSTX, medium-scale devices include a reverse-field-pinch experiment, MST, at the University of Wisconsin. There are tokamaks, including the DIII-D machine at General Atomics and the Alcator-C machine at MIT. PPPL is leading a national team that has just completed the conceptual design of a compact stellarator proof-of-principal experiment that will be proposed for construction. This configuration offers very stable, steady operation. There are scientific issues that are common to all of these configurations, so they support each other in their research. However, there are aspects of the different configurations that complement one another, enabling a deeper understanding of the science. If one of these ideas works out better than others, it may race ahead of the rest. Ultimately the best configuration will be selected for the first fusion demonstration power plant. ES News:What are the next steps toward a fusion power reactor? Goldston: In addition to optimizing the plasma configuration, these are likely to include a burning (self-heated) plasma experiment, an engineering test facility, facilities for testing fusion materials and components, and then a demonstration plantwhich would put net electricity onto the grid. It may be possible to eliminate one step by combining the burning plasma experiment and engineering test facility into one devicethe cost of which would be shared through international collaboration. The spherical torus configuration, being developed through NSTX, may provide an excellent test bed for the development of materials and components for the demonstration power plant. One of the primary missions of the engineering test facility would be to study the effect of fusion neutrons on plasma facing components, including the blanket or first wall surrounding the plasma. The blanket would capture the neutrons and convert their kinetic energy to heat. The demonstration plant would have the ability to use the heat produced in the blanket to make steam and perhaps generate as much as 500 million watts of electric power. ES News: People are concerned about the safety of nuclear power. Tell us why fusion power may be safer than fission. Goldston: In a fission power plant, you need to have one or two years' worth of fuel in the reactor vessel. But the amount of fuel in the reaction chamber of a fusion power plant is only a few minutes' worth. Radioactivity will be produced by neutrons interacting with the reactor structure, but careful materials selection is expected to minimize the handling and ultimate disposal of such activated materials. ES News: What is the status of international collaboration in fusion research? Goldston: As usual, there is a tremendous amount of collaboration and cooperation among the various nations with fusion programs. U.S. physicists spend time, especially in Europe and Japan, working on their fusion experiments, and their researchers work on our devices. These collaborations insure the free, expeditious flow of research results and, of course, are in addition to the transfer of information through publication in scientific journals. I should add that many of the papers that appear are authored by individuals representing several labs worldwide.
The Europeans, Japanese, Canadians, and Russians are moving ahead with the proposal to build a burning plasma/engineering test facility called ITER. The U.S. dropped out of this cooperative effort in 1998 for budgetary reasons. Making ITER a strong part of the U.S. program will require the nation to become more committed to energy issues, particularly fusion energy. We'll see how that evolves in 2002, but I am cautiously optimistic. ES News: What is the current budget for the U.S. Fusion Energy Sciences Program? Goldston: We will spend about $250 million in fiscal year 2002. Europe and Japan together are spending about a billion dollars a year. Yet, together, their economies are only 40% larger than ours. India and China also have substantial programs in fusion. Korea is building a $400 million fusion experiment right now. My worry is that if we don't move forward more aggressively in fusion, the U.S. will be buying fusion reactors from another country. There's a big transfer of wealth when you buy a power plant from somebody else. I argue strongly for international collaboration in fusion energy science research. We are still in the pre-competitive phase of developing the physics and technology, and it's good for the whole world to be working together to develop fusion. At some future time, the teams are going to divide up and say, "I'm going to build mine and sell it cheaper than you." I wonder if we are going to be among those who are ready to go, or are we going to be left behind? ES News: Have budget reductions for the fusion program discouraged students from choosing careers in fusion science? Goldston: Recently funding has been stable, or even growing, which is encouraging after the difficult times of the mid 1990's. The goal of fusion energy is sufficiently attractive and the interest in plasma science is sufficiently strong that we continue to get wonderful students. Every year a few are so clever and understand things so quickly, and are so enthusiastic, that they knock our socks off. If the fusion program were growing faster, it would be easier to keep a larger fraction of these students in the program after they complete their graduate degrees. But then, some of them are so good, we find a place for them. Professor Rob Goldston came to PPPL as a graduate student in 1972 after receiving his bachelor's degree, magna cum laude, from Harvard University. He served as a research assistant at the Lab for five years and earned his Ph.D. in astrophysics, Program in Plasma Physics, from Princeton University in 1977. Over the next 15 years, he advanced in progressively responsible positions on the PPPL research staff. He has had a distinguished career pursuing experimental and theoretical research on the high-temperature plasmas required for producing thermonuclear fusion. Goldston was named professor of astrophysical sciences at Princeton University in 1992, a position he continues to hold, and Associate Director for Research at PPPL in 1995. In 1997, he became the Laboratory's fifth Director. Professor Goldston is the author and coauthor of more than 200 scholarly articles, and is coauthor with Paul Rutherford of the textbook, Introduction to Plasma Physics. |
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