UW Dynomak fusion reactor concept cheaper than coal

The UW's current fusion experiment, HIT-SI3. 

It is about one-tenth the size of the power-producing dynomak concept. 

Credit: U of Washington

Fusion energy almost sounds too good to be true – zero greenhouse gas emissions, no long-lived radioactive waste, a nearly unlimited fuel supply.

Perhaps the biggest roadblock to adopting fusion energy is that the economics haven't penciled out.

Fusion power designs aren't cheap enough to outperform systems that use fossil fuels such as coal and natural gas.

University of Washington engineers hope to change that. They have designed a concept for a fusion reactor that, when scaled up to the size of a large electrical power plant, would rival costs for a new coal-fired plant with similar electrical output.

The team published its reactor design and cost-analysis findings last spring and will present results Oct. 17 at the International Atomic Energy Agency's Fusion Energy Conference in St. Petersburg, Russia.

"Right now, this design has the greatest potential of producing economical fusion power of any current concept," said Thomas Jarboe, a UW professor of aeronautics and astronautics and an adjunct professor in physics.

The UW's reactor, called the dynomak, started as a class project taught by Jarboe two years ago.

After the class ended, Jarboe and doctoral student Derek Sutherland, who previously worked on a reactor design at the Massachusetts Institute of Technology (MIT), continued to develop and refine the concept.

UW's dynomak

The design builds on existing technology and creates a magnetic field within a closed space to hold plasma in place long enough for fusion to occur, allowing the hot plasma to react and burn.

The reactor itself would be largely self-sustaining, meaning it would continuously heat the plasma to maintain thermonuclear conditions.

Heat generated from the reactor would heat up a coolant that is used to spin a turbine and generate electricity, similar to how a typical power reactor works.

"This is a much more elegant solution because the medium in which you generate fusion is the medium in which you're also driving all the current required to confine it," Sutherland said.

There are several ways to create a magnetic field, which is crucial to keeping a fusion reactor going.

The UW's design is known as a spheromak, meaning it generates the majority of magnetic fields by driving electrical currents into the plasma itself.

This reduces the amount of required materials and actually allows researchers to shrink the overall size of the reactor.

Other designs, such as the experimental fusion reactor project (tokamak) that's currently being built in France, called Iter, have to be much larger than the UW's because they rely on superconducting coils that circle around the outside of the device to provide a similar magnetic field.

When compared with the fusion reactor concept in France, the UW's is much less expensive, roughly one-tenth the cost of Iter, while producing five times the amount of energy.

Iter's Tokamak

The UW researchers factored the cost of building a fusion reactor power plant using their design and compared that with building a coal power plant.

They used a metric called "overnight capital costs," which includes all costs, particularly startup infrastructure fees.

A fusion power plant producing 1 gigawatt (1 billion watts) of power would cost $2.7 billion, while a coal plant of the same output would cost $2.8 billion, according to their analysis.

"If we do invest in this type of fusion, we could be rewarded because the commercial reactor unit already looks economical," Sutherland said. "It's very exciting."

Right now, the UW's concept is about one-tenth the size and power output of a final product, which is still years away.

The researchers have successfully tested the prototype's ability to sustain a plasma efficiently, and as they further develop and expand the size of the device they can ramp up to higher-temperature plasma and get significant fusion power output.

The team has filed patents on the reactor concept with the UW's Center for Commercialization and plans to continue developing and scaling up its prototypes.

PPPL QUASAR Stellerator: A concept on the path to fusion energy

QUASAR stellerator design. Credit: PPPL

Completion of a promising experimental facility at the U.S. Department of Energy's Princeton Plasma Laboratory (PPPL) could advance the development of fusion as a clean and abundant source of energy for generating electricity, according to a PPPL paper published this month in the journal IEEE Transactions on Plasma Science.

The facility, called the Quasi-Axisymmetric Stellarator Research (QUASAR) experiment, represents the first of a new class of fusion reactors based on the innovative theory of quasi-axisymmetry, which makes it possible to design a magnetic bottle that combines the advantages of the stellarator with the more widely used tokamak design.

Experiments in QUASAR would test this theory.

Construction of QUASAR, originally known as the National Compact Stellarator Experiment (NCSE), was begun in 2004 and halted in 2008 when costs exceeded projections after some 80 percent of the machine's major components had been built or procured.

George "Hutch" Neilson

"This type of facility must have a place on the roadmap to fusion," said physicist George "Hutch" Neilson, the head of the Advanced Projects Department at PPPL.

Both stellarators and tokamaks use magnetic fields to control the hot, charged plasma gas that fuels fusion reactions.

While tokamaks put electric current into the plasma to complete the magnetic confinement and hold the gas together, stellarators don't require such a current to keep the plasma bottled up.

Stellarators rely instead on twisting, or 3D, magnetic fields to contain the plasma in a controlled "steady state."

Stellarator plasmas thus run little risk of disrupting or falling apart as can happen in tokamaks if the internal current abruptly shuts off.

ITER: the world's largest Tokamak

Developing systems to suppress or mitigate such disruptions is a challenge that builders of tokamaks like ITER, the international fusion experiment under construction in France, must face.

Stellarators had been the main line of fusion development in the 1950s and early 1960s before taking a back seat to tokamaks, whose symmetrical, doughnut-shaped magnetic field geometry produced good plasma confinement and proved easier to create.

But breakthroughs in computing and physics understanding have revitalized interest in the twisty, cruller-shaped stellarator design and made it the subject of major experiments in Japan and Germany.

PPPL developed the QUASAR facility with both stellarators and tokamaks in mind. Tokamaks produce magnetic fields and a plasma shape that are the same all the way around the axis of the machine—a feature known as "axisymmetry." QUASAR is symmetrical too, but in a different way.

While QUASAR was designed to produce a twisting and curving magnetic field, the strength of that field varies gently as in a tokamak, hence the name "quasi-symmetry" (QS) for the design.

This property of the field strength was to produce plasma confinement properties identical to those of tokamaks.

"If the predicted near-equivalence in the confinement physics can be validated experimentally," Neilson said, "then the development of the QS line may be able to continue as essentially a '3D tokamak.'"

More information: Neilson, G.H.; Gates, D.A.; Heitzenroeder, P.J.; Breslau, J.; Prager, S.C.; Stevenson, T.; Titus, P.; Williams, M.D.; Zarnstorff, M.C., "Next Steps in Quasi-Axisymmetric Stellarator Research," Plasma Science, IEEE Transactions on , vol.42, no.3, pp.489,494, March 2014. DOI: 10.1109/TPS.2014.2298870