A company in Oxfordshire, U.K., is aiming to make a business out of fusion with a design for a super compact fusion reactor, or tokamak, that it hopes to sell to industry or for research. The reactors are not designed to generate power but to exploit the fact that fusion reactions produce lots of high-energy neutrons, which can be used to make medical isotopes, transmute nuclear waste, and for research on plasma and materials. To produce neutrons in large quantities usually requires a fission reactor or powerful particle accelerator, so a relatively cheap fusion neutron source could open up many possibilities. Also, the size and cost of conventional tokamaks means that they are usually built by government research labs. Attempts to commercialize fusion are rare.
Physicist and entrepreneur David Kingham, chief executive of the new company Tokamak Solutions, says that the firm could build the most basic version of the machine—producing just a hot plasma for research purposes—in a year at a cost of around $1 million. Swadesh Mahajan of the Institute for Fusion Studies at the University of Texas, Austin, welcomes the creation of the company but says: "It's going to be difficult to predict if there is a market for [such a] machine."
Governments around the globe have been building tokamaks for more than 40 years in an effort to generate power from fusing hydrogen nuclei together to form helium. A tokamak is a doughnut shaped vessel in which the hydrogen gas is ionized, squeezed, and heated with intense magnetic fields until fusion takes place. The world's largest tokamak, the 6-meter wide ITER currently under construction in France, is expected to be the first that will produce large amounts of excess energy, but at a cost of around €15 billion.
Spherical tokamaks are variants on the traditional doughnut design, shaped instead like a cored apple. They are cheaper to build and the ionized gas, or plasma, they produce tends to be more stable than in conventional machines. The United Kingdom's Culham Laboratory, now known as the Culham Centre for Fusion Energy, built the first spherical tokamak, START, from 1990 to 1991. Since then, some 15 spherical tokamaks have been built worldwide.
Mikhail Gryaznevich and Alan Sykes, fusion scientists who have worked at Culham for 20 years, teamed up with Kingham in 2009 to form Tokamak Solutions, believing there must be a market for small, cheap, and reliable tokamaks. This week they announced that they had secured £170,000 from various sources to develop a full conceptual design over the next year.
Kingham says they will take a stepwise approach: first developing a simple plasma reactor that is 1.5 meters in external diameter. This would partly be a demonstrator, but "plasma physics labs could find interesting things to do with it," he says. Because the reactor is not aiming to generate power from fusion, the design does not require the extremes of temperature and magnetic field that the likes of ITER produce. "We're not pushing too many boundaries of known technology," Kingham says.
The next stage would be to build a device that generates neutrons by fusing deuterium, a hydrogen isotope. This will require additional heating of the plasma, which they will achieve by firing high-energy beams of neutral hydrogen into the tokamak. The beam heats the plasma to fusion temperatures and also generates fusions in its initial collision with the hot gas. "We may get more neutrons from the impact than from the plasma," Kingham says. This sort of machine could be useful to medical physicists trying to develop new radioisotopes for medical treatments.
In the final phase they aim to make a machine that uses a mixture of deuterium and tritium, another hydrogen isotope, a more reactive combination. But tritium, a radioactive gas, has to be handled very carefully. This stage will be "significantly more challenging," Kingham says. The team's modelling suggests that they will be able to generate neutrons with a combined power in the megawatts, and more cheaply than other types of neutron source such as fission reactors or accelerator-based spallation sources.
Neutrons from the source they envision would be able to transmute dangerous and long-lived nuclear waste, particularly minor actinides, into more manageable forms. They could also be used to test materials needed for future fusion or fission power reactors. A spherical tokamak could even form the core of a hybrid fusion-fission reactor, providing the neutrons to keep a fission reaction running. "Our expertise is in neutron sources and small tokamaks. We need to find the right partners and work with them to develop applications," Kingham says.
The basic machine in a university physics department "would be a nice interesting tool for learning some aspects of plasma physics, if sufficiently cheap," Mahajan says. "But a neutron source of some significance is not a minor thing … the jury is still out."