CAMBRIDGE, Mass.--Just a few blocks off busy Massachusetts Avenue there is a lab devoted to nuclear fusion, the science of fusing atoms together to create energy. Although it's largely outside the daily discussions on energy, fusion is still being actively pursued. There are other types of fusion being studied, but a tour of the facility introduced me to the fundamentals of magnetic fusion and some of the technical challenges.
Pictured here is the blue cylinder-shaped test reactor. Inside is a doughnut-shaped vessel measuring about 1 meter across in the middle. Researchers are able to fuse two hydrogen atoms to make helium but only for a few seconds. An interesting side note is that only a few blocks away is MIT's nuclear research reactor built at the dawn of the atomic age to study nuclear fission, or splitting atoms to produce energy.
For related story, see "A reality check on nuclear fusion at MIT."
One of the big technical challenges to magnetic nuclear fusion is finding materials that can withstand the super high temperatures--millions of degrees Celsius--and magnetic fields required for a reaction. Pictured here is a device to test the effect of plasma on different materials. The plasma is the pink beam shining on a circular metal test surface.
Plasma is a state of matter which happens at high temperatures--this plasma was created at 50,000 degrees Celsius--where electrons break off from an atom's nucleus. To get nuclear fusion, MIT and other researchers need to create plasma of two hydrogen isotopes (heavier versions of hydrogen) and heat the vessel so that fusion occurs. The vessel has powerful magnetic fields to confine plasma and keep it away from the vessel walls, but particles and heat leak out. That's one reason that materials science and testing is important to the future of fusion.
MIT professor of nuclear science and engineering Dennis Whyte, pictured here, helped lead a tour of MIT's Plasma Science and Fusion Center. He believes that a power plant able to produce electricity with fusion could be built in 10 to 15 years with an annual research budget of $20 billion, but the machine would probably not be reliable or economic, he said. The prevailing view is that nuclear fusion needs to be pursued for decades before a practical energy-producing system can be made.
Behind him are incredibly close-up images, or micrographs, of the surface of materials from inside a nuclear fusion reactor. With so much heat and electromagnetic energy, materials get melted and damaged, even tungsten which has the highest melting point.
Here is an image captured from the doughnut-shaped test reactor at MIT. This magnetic fusion reactor fuses two heavy isotopes of hydrogen to produce helium and a blast of energy. In a working power plant, the heat from the making of helium would be fed back into the reactor to sustain the reaction. The other product of fusion is neutrons which fire off after fusion. The idea is to convert the kinetic energy from those neutrons into electricity by making steam, which would drive a turbine as today's power plants do.
The MIT nuclear fusion reactor is a tokamak design, which you can see here in this cutaway drawing which is hanging in the center. A tokamak, which used to stand for a Russian acronym, uses powerful magnetic fields to keep plasma from touching the surface of the vessel. The magnetic fields are produced by the coils that surround the doughnut-, or torus-, shaped vessel. The entire construction is about 15 feet tall and the torus is about 3 feet across in the middle. ITER is a global collaboration that has plans to build a much larger magnetic fusion reactor in southern France by the end of the decade.
MIT nuclear science and engineering graduate student Matt Reinke stands in front of a model of the nuclear fusion reactor's cover, which gives you an idea of how big it is. These covers actually bend during the maximum pulses.
Here is the control room for the test nuclear fusion reactor, where experiments are regularly done for MIT students and researchers. The tests, which are run by two people, generate data on the temperature and magnetic field inside the reactor as well as the properties of the high-temperature plasma. Each "shot" lasts only a few seconds and it takes about 15 minutes for the reactor to cool down for the next shot.
One of the high-level goals of these tests is to figure out an operating mode that removes particles which can "poison" the fusion process.
A closer view of the test reactor which shows how many diagnostic probes and instrumentation are attached to the tokamak. A two-second pulse of power to set off fusion generates gigabtyes of data, said nuclear science and engineering student Matt Reinke. Over the years, terabytes of information have been generated. People actually go in that opening to attach diagnostic equipment and it's a very tight space.
This photo provides a view of what the interior of the doughnut-shaped reactor vessel is like. Strong magnetic fields are created by coils around this structure and antennas create the high heat to precipitate fusion. Often, the interior of the tokamak vessel are made from tungsten, but the MIT's Alcator C-Mod machine uses molybdenum.
There is a separate lab to test how materials will stand up to the high energy from nuclear fusion. Plasma is created by heating up hydrogen gas with radio waves to about 50,000 degrees Celsius. That plasma in then put into a vacuum, as it would be in a reactor to perform tests. A machine attached to this shoots high-energy ion beams onto the surface of a material, such as tungsten, to see with great definition the effect of plasma on the surface. The goal is design a system where the material does not degrade and cause problems.
One area of research is to see how helium, which is produced during fusion of two hydrogen isotopes, affects the materials inside nuclear fusion reactors. These photos show how small filaments form on the surface of tungsten which is used on the interior of fusion reactors. By studying how helium degrades from the energy produced from fusion, researchers hope to develop reliable materials for reactors.
Nuclear fusion testing at MIT relies on powerful magnetic fields and temperatures in the millions of degrees. That requires huge bursts of power, on the order of megawatts for a few seconds. Since the test fusion reactor is in the middle of Cambridge, it can't draw that much power directly from the grid without affecting its neighbors, so it has an alternator which stores power like a flywheel to deliver the power, said Matt Reinke, nuclear science and engineering student, during a tour.
Inside the control room is this bolt which gives you an idea of the size of the reactor and the magnetic thrust. Two of these bolts would be able to hold down the thrust of the Space Shuttle and the reactor has 96 in all.