Canadian firm pursues mechanical approach to fusion energy

A successful test of this scaled down prototype of General Fusion’s reactor may change the future of energy production.

In a world beset by fossil fuel energy woes, fusion energy is holiest of Holy Grails. A working fusion reactor would not only release large amounts of energy but, unlike nuclear fission plants, they can’t melt down. They’re also significantly “cleaner,” in that a fusion reaction only uses small amounts of an abundant fuel (hydrogen isotopes tritium and deuterium), which is only weakly radioactive. The problem is, no one has yet created a net gain reactor (more energy out than in), although many well-funded programs are actively pursuing it.

It’s not surprising, considering the daunting challenges involved. Similar to the process that drives the Sun, a fusion reaction—melding two hydrogen atoms to form helium—requires heating the reactor fuel to galactic-scale temperatures and crushed under intense pressures. Of course, you also need a vessel capable of producing and containing these thermonuclear conditions.

Consequently, building fusion reactors will take decades, as well as enormous expenditures, which is why enthusiasm for this type of energy production has dampened. However, these same issues have many in the field keeping a close eye on a Canadian company, General Fusion, and its comparatively low-tech approach to fusion power. The Burnaby, BC-based company’s mechanical design sidesteps the massive costs of other leading approaches.

“Fusion reactions require plasma to be heated to near 150 million˚C, and that requires a lot of energy,” says Michael Delage, General Fusion’s vice president of business development. “Where you get this energy, and how you deliver it to the fuel, has a big effect on system cost.”

Reactor Design 101
To appreciate General Fusion’s concept, it’s important to understand how it differs from the two leading projects. ITER, a multinational collaboration based in France, is the larger and uses an approach called magnetic confinement. Using this method, a stream of super-heated tritium and deuterium gas, or plasma, is contained in a donut-shaped vacuum vessel called a tokamak. Super conducting magnets heat and compress the plasma to create the fusion reaction.

The National Ignition Facility (NIF) at Lawrence Livermore National Laboratories is pursuing the other approach, inertial confinement. It employs 192 laser beams focused on deuterium-tritium pellets inside a 10-meter-diameter target chamber to convert the fuel to plasma and generate X-rays. The radiation then compresses the plasma until fusion occurs. Both methods, says Delage, require massive amounts of input energy and depend on expensive, complex equipment that drive development costs into the billions and time lines out to 2050 at best.

In comparison, Delage says a commercial General Fusion reactor could be online by 2020 and at a fraction of the price. The company’s approach is a hybrid between the two main methods, called “magnetized target” fusion, and employs a comparatively less power hungry reactor design. Based on a concept called LINUS first developed by the U.S. Naval Research Laboratory in the 1970s, General Fusion’s reactor starts with a spherical vessel filled with liquid lead-lithium metal. The liquid metal is then pumped in a circle until centrifugal force forms a vortex in its center.

Into this vortex, plasma injectors on the top and bottom of the reactor inject doughnut-shaped “puffs” of plasma wrapped in a magnetic field. Like smoke rings blown into either end of a tube, these “magnetized targets” collide at the reactor’s core. As the targets combine, approximately 200 steam-driven pistons simultaneously hammer the spherical vessel, sending a shockwave through the molten metal. The shockwave collapses the vortex and compresses the plasma, heating it adiabatically (like a diesel engine), to produce a short burst of fusion energy.