Fusion 24 - Germany About To Turn On Experimental Stellerator For Nuclear Fusion
I have been blogging recently about fusion research in the United States. There has been global research on fusion reactors for decades largely based on what is called a "tokamak." The ITER project in France is an international collaboration that has spent billions of dollars building a giant version of a tokamak type fusion reactor. It is way over budget and way behind schedule. Germany has spent over one billion dollars to construct the biggest version of a "stellerator" type fusion reactor in existence.
A tokamak is a donut shaped chamber where a plasma is compressed to create a fusion reaction. The chamber is smoothly symmetrical and a powerful current flows through the plasma to compress it. The stellerator design is also shaped like a donut but it is not symmetrical like a tokomak. Instead, it has a five lobed configuration. The plasma in a stellerator is compressed by external magnetic fields. Stellerators are much more complex and difficult to construct than tokamaks but they are inherently more stable and may be better for power generation. Only a few stellerators have been built as opposed to the over two hundred tokamaks that have been constructed.
A major difference between a tokamak and a stellerator is the fact that the tokomak design cannot be run continuously. The longest operation of a tokamak so far was a French reactor that ran for a total of six and a half minutes. A tokamak has never been able to produce more energy than it has required to operate. This limitation means that a tokamak would not be a viable candidate for a commercial power reactor.
Germany's stellerator is called the Wendelstein 7-X or W7-X. This machine has a twisted torus plasma chamber. It is fifty two feet wide and weighs about four hundred and twenty five tons. There are fifty superconducting magnets that each weigh five and one half metric ton around the torus that are cooled by liquid helium. Over a million man hours were required to build the W7-X. It has over two hundred and fifty ports for observation and injecting plasma into the hollow ring at the center of the torus. The researchers working on the W7-X stellerator hope that it will be able to run for at least thirty minutes at a time. This would be a break-through for fusion research. The German team expects to turn on the W7-X soon.
The ITER and the W7-X are following the model of the giant nuclear fission power reactors. Any commercial power reactor based on the W7-X would cost billions of dollars, be difficult and time consuming to construct and would have to generate gigawatts to be cost effective. At least six companies in the U.S. are working on novel designs different from the research tokomaks and stellerators being build and tested. This new generation of fusion reactors will be much smaller and cheaper than the ITER or the W7-X. They will generate less power but will be simple and easy to build in comparison. It seems to me that both the ITER project and the W7-X project are outdated wastes of money.
Artist's rendition of the shape of the magnetic confinement inside the W7-X stellerator:
