It’s Nice to Dream

Since I was in college I’ve been reading reports of fusion reactors that were just around the corner. That was more years ago than I care to mention. Now just today I’m reading of two projects that should have prototypes working within a few years. First, from Aviation Week:

To understand the breakthroughs of the Lockheed concept, it is useful to know how fusion works and how methods for controlling the reaction have a fundamental impact on both the amount of energy produced and the scale of the reactor. Fusion fuel, made up of hydrogen isotopes deuterium and tritium, starts as a gas injected into an evacuated containment vessel. Energy is added, usually by radio-frequency heating, and the gas breaks into ions and electrons, forming plasma.

The superhot plasma is controlled by strong magnetic fields that prevent it from touching the sides of the vessel and, if the confinement is sufficiently constrained, the ions overcome their mutual repulsion, collide and fuse. The process creates helium-4, freeing neutrons that carry the released energy kinetically through the confining magnetic fields. These neutrons heat the reactor wall which, through conventional heat exchangers, can then be used to drive turbine generators.

Until now, the majority of fusion reactor systems have used a plasma control device called a tokamak, invented in the 1950s by physicists in the Soviet Union. The tokamak uses a magnetic field to hold the plasma in the shape of a torus, or ring, and maintains the reaction by inducing a current inside the plasma itself with a second set of electromagnets. The challenge with this approach is that the resulting energy generated is almost the same as the amount required to maintain the self-sustaining fusion reaction.

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 burst—so to operate safely, they don’t 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. “It’s 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 we’ve 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.

They’re talking about five years to prototype and ten to production.

And then there’s this in EETimes Europe:

Fusion reactors offer the possibility of unlimited green power, being based on the same principles that make the sun shine. Instead of fission reactors that produce massive amounts of radioactive waste that must be stored for thousands of years, fusion reactors produce only a small amount of much less dangerous nuclear waste that only has to be stored for 10 years. Fusion reactors also do not present the danger of a melt down. Sutherland’s and Jarboe’s low-cost fusion reactor design will be presented at the International Atomic Energy Agency’s Fusion Energy Conference in St. Petersburg, Russia on October 17, 2014.

The design, called a spheromak, began as a class project by professor Thomas Jarboe, but had not been proven a viable design until a prototype called the Dynomak was recently built by Jarboe and doctoral candidate Derek Sutherland, who had previously worked on reactor designs at the Massachusetts Institute of Technology (MIT).

The standard approach to fusion reactors today, exemplified by the joint Chinese, European Union, India, Japan, Korea, Russia, and US collaboration called the International Thermonuclear Experimental Reactor (ITER) in Saint-Paul-lès-Durance, France, is akin to using brute force compared to the more elegant Dynomak design invented at University of Washington.

“We eliminated the need for the expensive superconducting toroidal field coil set like the ITER in France requires, enabling us to make a much more compact reactor system that reduces the cost by a factor of 10 while increasing the output by a factor of five,” Sutherland told EE Times. “The spheromak design generates twisted magnetic fields which drive a current in the plasma — which is a really good conductor
— thereby confining and stabilizing the super-hot plasma in the reactor. A voltage transferred using induction generates these magnetic fields to achieve confinement and stability.”

There’s no estimate on how long it will take to build the next generation prototype or a production model.

I wouldn’t advise selling your stock in Peabody just yet. We’ve had reports like this for decades. But it’s certainly intriguing.

Imagine a fusion power generation plant cheaper to build than a coal-fired plant, which produces no greenhouse gases, and which doesn’t pose a radiation (or security) hazard. I think we’d probably learn pretty quickly whether environmentalists were interested in the environment or just opposed to technology.