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This story appeared first in the Sunday edition of the Wisconsin State Journal newspaper.

As the world watched a nuclear crisis slowly unfold in Japan, UW-Madison scientists continued working on technology that could someday produce nuclear power without radioactive waste.

"It's the holy grail of alternative energy research," said Robert Wilcox, a graduate student working on one of several UW-Madison fusion projects.

In a fusion reaction, superheated atoms are joined to give off energy, as opposed to fission, in which the energy is released when atoms are broken apart. At UW-Madison, dozens of researchers are studying fusion to better understand and control the superhot substances in which the reactions take place.

The work is garnering national and international attention. In December, two projects won $10.7 million in competitive grants from the U.S. Department of Energy. And UW-Madison researchers are part of an international group working to build the world's first fusion power plant in France. In fact, scientists say, the work in Madison is crucial to the success of that effort because researchers here are working on problems that could delay the international project if they are not solved.

"It's the energy of the stars," said David Anderson, a UW-Madison computer and electrical engineering professor who oversees one of UW-Madison's fusion projects. "It's the energy of the future."

Superheated hydrogen

Researchers at UW-Madison are studying fusion by working with hydrogen superheated into plasma, a fourth state of matter in which the hydrogen molecules fuse after the plasma is ignited and heated to 100 million degrees or more. 

By studying plasma — how to more efficiently ignite it and how to better control and contain it — UW-Madison researchers hope to bring us closer to the day when much of our electrical power could be safely generated by fusion.

That could happen in about 50 years or so, researchers said. While a number of smaller research reactors are in operation around the world, a commercial-sized reactor that can generate electricity has yet to be built because of problems including the amount of energy necessary to start and sustain a reaction, and the difficulties designing a vessel to contain the reaction. 

Why so much interest in fusion?

To understand the answer to that question, it's important to understand how fusion differs from fission, which is the kind of reaction that powers current nuclear plants. In nuclear fission, an atom's nucleus is split into two fragments. In nuclear fusion, the nuclei of light atoms, such as hydrogen and helium, are fused to create a heavier nucleus. It's the same kind of reaction that powers the sun and other stars. Both reactions release energy because of the change in mass. 

No radioactive waste 

Several characteristics of fusion eliminate some of the safety problems of traditional fission plants that became apparent as the situation in Japan worsened. There, damage to the reactors and waste storage pools caused the nuclear fuel to overheat and release radioactive material into the air and water.

Anderson said one major problem with nuclear fission is that even when you stop the reaction, several of the radioactive byproducts can continue to generate heat for days and even weeks. With fusion, once the reaction is stopped, the generation of heat stops so there is no threat of the reactor melting down.

"The whole idea is that once you terminate the reaction, which is hard to get going in the first place, there is no more heat produced and everything returns to a relatively safe state. So loss of cooling isn't really a problem," Anderson said.

Unlike fission, the process of fusion does not result in the large and long-lasting amounts of dangerous waste because the major byproduct of a fusion reaction is helium, which is not radioactive. "You can use it to fill circus balloons. You can breathe it and talk like Mickey Mouse," Anderson said.

So there would be no need to store radioactive waste for thousands of years, an issue that has nearly brought the construction of nuclear fission plants to a standstill.

Another advantage of fusion is the plasma used to create the reaction is superheated hydrogen. Hydrogen is readily available from sea water, and the process produces no materials that could be used as weapons.

Two types of reactor vessels

UW-Madison is home to a number of ambitious fusion research programs. They include about 75 faculty and staff, 60 graduate students and 30 undergraduate students.

Fusion researchers on campus are using two kinds of reactor vessels. Anderson is using a two-story device called the Helically Symmetric eXperiment, or HSX. Deep in Engineering Hall, the unique reactor, also known as a stellarator, seems a confusing tangle of steel beams and heavy copper coils adorned with dozens of monitoring instruments. 

Anderson and the HSX crew were awarded about $6 million of the $10.7 million Department of Energy grant.

About $4.7 million went to another UW-Madison fusion reactor called Pegasus, a type of reactor vessel called a tokomak. It is a slightly different and much smaller version of the type of reactor being built in France as part of an international fusion research effort, said Raymond Fonck, UW-Madison Steenbock Professor of Physical Science and a professor of engineering physics.

Both reactors generate the superhot plasma that can be used to fuse hydrogen atoms. But there are crucial differences that are important to the research agendas of each; the differences have to do with how the plasma in which fusion reactions take place is contained and controlled.

Work with the Pegasus reactor vessel — known as a toroidal reactor because of its donut shape — is crucial to the international effort because it allows researchers to study the containment of plasma on a smaller and more manageable scale than the larger reactor that will be built in France. The grant money, Fonck said, will allow researchers to study plasma in the device at higher electrical current and higher temperatures.

"It's making that jump to the next level of activity so we can uncover the physics that may show up," Fonck said.

Pegasus researchers also are trying to understand mysterious burps in burning plasma that so far have gone unexplained and have the potential to cause big problems at a larger scale. Fonck described the disturbances as an explosive ejection of the outermost layer of plasma, "almost like an onion that blows off its outer skin." 

Anderson's HSX device is important because its design is different than the tokomak vessel. Instead of being shaped like a perfectly round donut, HSX is oddly twisted. But that shape — and the complicated spaghetti-like tangle of copper coils around the outside of the vessel — allow the plasma to be contained without using the powerful electrical current used in a tokomak.

The unique design makes the HSX stellarator a possible alternative to the tokomak because of the stability it lends to the confined plasma. 

"Wisconsin is in a leadership position when it comes to such alternatives," Anderson said.

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