An experimental U.S. facility completed by the Department of Energy could bring electricity generated by abundant and clean fusion power one step closer, scientists say.
The facility, Quasi-Axisymmetric Stellarator Research experiment, or QUASAR, was developed at the DOE's Princeton Plasma Laboratory.
It is an example of a type of fusion reactor based on a theory known as quasi-axisymmetry, leading to the design of a magnetic "bottle" -- necessary to contain and control a fusion reaction -- combining advantages of a stellarator and a more usual tokamak design.
Both designs utilize magnetic fields to contain the extremely hot, charge-carrying plasma gas created in fusion reactions.
Tokomaks require electric current to be fed into the plasma to create a magnetic confinement to hold the gas tightly together, while stellarators don't require the same process to keep the plasma contained.
Instead they rely on twisted 3D magnetic fields to harness and control the plasma in a "steady state."
The QUASAR experiment is intended to test the effectiveness of the stellarator concept and compare it to the tokomak paradigm.
It had been initiated in 2004 but brought to a halt in 2008, after a majority of its major components had been constructed, when costs went beyond projections.
Now completed, it has put stellerators -- the center of fusion research in the 1950s and 1960s but shoved aside by tokomaks that produced excellent plasma containment while being easier to build -- back on the fusion agenda.
"This type of facility must have a place on the roadmap to fusion," says Physicist George "Hutch" Neilson of the PPPL's Advanced Projects Department.
One perceived advantage of stellarators is that the plasma inside them are not prone to disrupting or coming apart as can occur in a tokomak if its internal electrical current is suddenly lost or shut off.
Just such a problem has plagued many tokomak systems; an international team working to built ITER, a fusion experiment in France, is having to devote considerable time and attention to developing systems to deal with such distruptions.
Advances in physics and computing have brought renewed interest in the stellarator design, with major work on stellarators underway in Germany and Japan.
With the Princeton stellarator, scientists are hopeful they can create properties of plasma confinement that measure up to those found in tokamaks.
"If the predicted near-equivalence in the confinement physics can be validated experimentally," Neilson says, "then the development of the QS [quasi-symmetry] line may be able to continue as essentially a '3D tokamak.'"
QUASAR-like designs might be a potential candidate for a demonstration version of a fusion reactor that could lead to building of a first commercial reactor to generate electricity, the researchers said.
The Princeton research has been described in the journal IEEE Transactions on Plasma Science.
