Defense contractor Lockheed Martin was recently awarded a patent for a novel design of compact nuclear fusion reactor, a device presumably small enough to be housed in a standard shipping container. According to earlier promotional material released by the company, the reactor’s compact design could be used not only for commercial energy-generating applications, but also incorporated into ocean-going ships and aircraft to vastly extend the vehicles’ ranges. In terms of generating electricity for commercial use, the device could also be used to replace not only nuclear waste-producing fission reactors, but also fossil fuel-based electrical generators, dramatically reducing the carbon footprint of our civilization’s thirst for energy.
Initially filed in April 3, 2013, the patent, US20180047462A1, illustrates the basic layout of a plasma confinement system with a linear arrangement, unlike the traditional doughnut shape used by tokamak reactor designs. The development of this device is presumably the same project being conducted by Lockheed’s secretive Advanced Development Programs (ADP), better known as Skunk Works, that was announced in a 2014 promotional video. In the video, MIT Skunk Works Compact Fusion Project Lead Thomas John McGuire says that the concept of a compact design allows them to speed up development of the reactor, meaning at the time the video was produced they expected to have a working prototype in five years, or 2019.
Most experimental fusion reactor designs are large and cumbersome by necessity: the extremely hot plasma used to fuel the fusion process would quickly melt through even the most robust of materials, meaning it has to be contained by powerful magnetic fields, generated by powerful superconducting magnets. For instance, the International Thermonuclear Experimental Reactor being developed in France is a large building-sized device weighing 26,000 tons; the MIT/Commonwealth Fusion Systems’ Sparc project, despite being much more compact, is still too large to be housed by anything smaller than a large ocean-going vessel. In contrast, Skunk Works’ device would be roughly the same volume as a small automobile.
The compact size of McGuire’s device is due to a novel design that improves the reactor’s ability to increase the pressure within the plasma: "The problem with tokamaks is that they can only hold so much plasma, and we call that the beta limit," according to McGuire. The beta limit is the ratio of the pressure within the plasma to the pressure being exerted by the reactor’s magnetic fields: tokamak reactors are only capable of a beta limit of 5 percent, so for every unit of pressure needed within the plasma, the device needs to generate a magnetic field with 20 units of pressure. If the reactor exceeds that limit, it loses containment, and the device fails spectacularly. Lockheed’s device makes use of a series of computer-controlled magnetic coils that adapt to changes in the plasma’s pressure, allowing the plasma to expand within the containment vessel, while the "walls" of the containment area strengthen in response. "So for us, instead of a bike tire expanding into air [that is at risk of bursting], we have something more like a tube that expands into an ever-stronger wall," McGuire explains. He feels that this novel approach can achieve a beta limit of 100 percent, and possibly even push beyond that 1/1 ratio.
It is estimated that Skunk Work’s reactor could run on 25 pounds (11 kilograms) of fuel, consisting of deuterium and tritium, for full year without needing to be refueled, and generate 100 megawatts of power over that period. Deuterium and tritium are naturally-occurring isotopes of hydrogen: deuterium is a non-radioactive substance, meaning it would have a negligible impact on the environment if a leak were to occur; and although tritium is radioactive, it has a half-life of only 12.32 years, meaning even a substantial amount of it would decay completely within a matter of centuries, as opposed to the hundreds of thousands of years that we expect the waste from fission reactors to plague us with.