I have been blogging this week about experimental fusion reactors. I got excited reading about the Bussard Polywell reactor. It has three excellent features. Based on hydrogen and boron-11 fuel, it does not consume radioactive fuel, it does not produce neutrons during operation and it does not produce radioactive waste. The developers of the Bussard Polywell say that they are confident that they can build a prototype 100 megawatt nuclear fusion reactor for about three hundred and fifty million dollars. This is a very small amount of money compared to the billions that are subsidizing the nuclear fission industry. But then I had to ask why one was not being built if it was such a good design.
The original idea for this type of reactor design was from a paper by a Russian physicist named Lavrent'ev published in 1974. Robert Bussard started a company to pursue the Polywell concept in 1985. In 1992 and 1994, he received funding from the U.S. Navy as well as two small grants from NASA and LANL. IN 1995, a paper was published by Todd Rider that offered a detailed criticism of the Polywell design. Because no operational device existed, Rider had to use theoretical estimates from other fusion research. After making a set of assumptions about the operation of the reactor including such factors as loss of ions due to upscattering, ion thermalization rate, energy loss due to x-ray emissions and the fusion rate, Rider concluded that the design had "fundamental flaws."
Bussard responded that the Polywell plasma had a different structure, temperature distribution and well profile than the operational parameters that had been assumed by Rider. He questioned other assumptions made by Rider and concluded that his design would produce net useful energy. Other researchers also questioned Rider's assumptions, calculation and conclusions. They pointed out that there were aspects of the Polywell design and operation that Rider did not address that undermined his conclusions.
I do not have the mathematical and physics background that would enable me to review Rider's critique and Bussard's answers. I would assume but cannot document that twenty years of work on experimental devices by the Polywell team should have experimentally answered some of the criticisms posed by Rider. However, the existence of a detail critique, even if flawed has had a corrosive effect on support for the project over the years.
Bussard continued to receive funding from the U.S. Navy from 1999 to 2006. He died in late 2007 while seeking funding to continue his work. In 2007, the Navy renewed funding and the project continued up to the present. The Polywell company is now seeking funds to build a full-scale model. Part of the problem with getting more money from the Navy lies in the fact that most of the nuclear research funded by the U.S. government is handled by the U.S. Department of Energy which supports the tokomak approach to nuclear fusion.
Considering how important this device could be if it works and the enormous amount of money the U.S. government spends on nuclear research, subsidies and loan guarantees, it would make sense to allocate the funds to build one. Assuming, of course, that the theoretical challenges from Rider and other have been successfully answered.
Diagram of a basic Polywell design:
