An advanced fusion reactor version, the International Thermonuclear Experimental Reactor (ITER), being built in Cadarache, France, is expected to generate 500 MW. However, plasma is not due to be generated until the late 2020s, and derivatives are not likely to be producing significant power until at least the 2040s.
The problem with tokamaks is that they can only hold so much plasma, and we call that the beta limit, McGuire says. Measured as the ratio of plasma pressure to the magnetic pressure, the beta limit of the average tokamak is low, or about 5% or so of the confining pressure, he says. Comparing the torus to a bicycle tire, McGuire adds, if they put too much in, eventually their confining tire will fail and burstso to operate safely, they dont go too close to that. Aside from this inefficiency, the physics of the tokamak dictate huge dimensions and massive cost. The ITER, for example, will cost an estimated $50 billion and when complete will measure around 100 ft. high and weigh 23,000 tons.
The CFR will avoid these issues by tackling plasma confinement in a radically different way. Instead of constraining the plasma within tubular rings, a series of superconducting coils will generate a new magnetic-field geometry in which the plasma is held within the broader confines of the entire reaction chamber. Superconducting magnets within the coils will generate a magnetic field around the outer border of the chamber. So for us, instead of a bike tire expanding into air, we have something more like a tube that expands into an ever-stronger wall, McGuire says. The system is therefore regulated by a self-tuning feedback mechanism, whereby the farther out the plasma goes, the stronger the magnetic field pushes back to contain it. The CFR is expected to have a beta limit ratio of one. We should be able to go to 100% or beyond, he adds.
This crucial difference means that for the same size, the CFR generates more power than a tokamak by a factor of 10. This in turn means, for the same power output, the CFR can be 10 times smaller. The change in scale is a game-changer in terms of producibility and cost, explains McGuire. Its one of the reasons we think it is feasible for development and future economics, he says. Ten times smaller is the key. But on the physics side, it still has to work, and one of the reasons we think our physics will work is that weve been able to make an inherently stable configuration. One of the main reasons for this stability is the positioning of the superconductor coils and shape of the magnetic field lines. In our case, it is always in balance. So if you have less pressure, the plasma will be smaller and will always sit in this magnetic well, he notes.
