Mug handles could help hot plasma give lower-cost, controllable fusion energy

October 11, 2012 by Hannah Hickey, University of Washington
This is a computer drawing of the prototype, which attaches current-carrying handles to either end of the central plasma. Credit: T. Jarboe, Univ. of Washington

(—New hardware lets engineers maintain the plasma used in fusion reactors in an energy-efficient, stable manner, making the system potentially attractive for use in fusion power plants.

Researchers around the world are working on an efficient, reliable way to contain the used in fusion reactors, potentially bringing down the cost of this promising but technically elusive source. A new finding from the University of Washington could help contain and stabilize the plasma using as little as 1 percent of the energy required by current methods.

"All of a sudden the current energy goes from being almost too much to almost negligible," said lead author Thomas Jarboe, a UW professor of aeronautics and astronautics. He presents the findings this week at the International Atomic Energy Association's 24th annual Conference in San Diego.

The new equipment looks like handles on a coffee mug – except they attach to a vessel containing a million-degree plasma that is literally too hot to handle. Most people know about , the commercial type of nuclear power generated from splitting large atoms in two. Still under research is , which smashes two small atoms together, releasing energy without requiring or generating radioactive waste.

Alternating the current through the handles produce asymmetric magnetic fields, shown here, which act to contain the plasma. Credit: T. Jarboe, Univ. of Washington

Of course, there's a catch – smashing the atoms together takes a lot of energy, and scientists are still working on a way to do it so you get out more energy than you put in. The sun is a powerful but we can't recreate a full-scale sun on Earth.

An international project in France is building a multibillion-dollar fusion reactor to see whether a big enough reactor can generate power.

The reactor in France will inject high-frequency and high-speed to sustain the plasma by maintaining an even hotter 100-million-degree operating temperature and enclosing it with magnetic fields.

"That method works," Jarboe said, "but it's extremely inefficient and expensive, to the point that it really is a major problem with magnetic confinement."

For two decades Jarboe's team has worked on helicity injection as a more efficient alternative. Spirals in the plasma produce asymmetric currents that generate the right electric and magnetic fields to heat and confine the contents. Plasma is so hot that the electrons have separated from the nuclei. It cannot touch any walls and so instead is contained by a magnetic bottle. Keeping the plasma hot enough and sustaining those magnetic fields requires a lot of energy.

"We would drive it until it was unstable," Jarboe said of his approach. "Like you twist up a rope, the plasma twists up on itself and makes the instability and makes the current drive."

Mug handles could help hot plasma give lower-cost, controllable fusion energy
Tom Jarboe has worked on fusion energy for more than three decades. The new copper handles can replicate the UW's low-energy approach while maintaining a stable plasma. Credit: Mary Levin, UW Photography

Results showed the UW strategy required less energy than other methods, but the system was unstable, meaning that if conditions change it could wobble out of control. It's like a stick balancing on one end, which is stable at that moment, but is likely to come crashing down with any nudge. In the case of plasma, unstable equilibrium means that a twist in the plasma could cause it to escape and potentially lead to a costly reactor shutdown.

Instability was a major impediment to applying the UW method.

"The big issue is whether, when you distort the bottle, it will leak," Jarboe said.

By contrast, in a stable equilibrium, any shift will tend to come back toward the original state, like a ball resting at the bottom of a bowl that will settle back where it started.

"Here we imposed the asymmetric field, so the plasma doesn't have to go unstable in order for us to drive the current. We've shown that we can sustain a stable equilibrium and we can control the plasma, which means the bottle will be able to hold more plasma," Jarboe said.

The UW apparatus uses two handle-shaped coils to alternately generate currents on either side of the central core, a method the authors call imposed dynamo current drive. Results show the plasma is stable and the method is energy-efficient, but the UW research reactor is too small to fully contain the plasma without some escaping as a gas. Next, the team hopes to attach the device to a larger reactor to see if it can maintain a sufficiently tight magnetic bottle.

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5 / 5 (2) Oct 11, 2012
A bit early to break out the bubbly, eh.
3.8 / 5 (5) Oct 11, 2012
Well it's money well spent, vs stupid little wars over oil, and/or democratizing countries that are too unstable to last (again for oil and other natural resources), and/or sustaining a large body of people that won't get off their collective asses and become productive citizens.

I hope this design or a spawn of it succeeds. Hot fusion is the word.
2.7 / 5 (3) Oct 11, 2012
This does look like a Go. I'll be keeping the fingers x'd.
4.7 / 5 (3) Oct 12, 2012
Sounds promising.

releasing energy without requiring rare elements or generating radioactive waste.
Well, sorta. While certainly vastly superior to fission in that department fusion does generate some radioactive waste (neutrons bombarding the containment vessel's walls do turn a percentage of the atoms therein into radioactive isotopes. So the containment vessel itself is 'radioactive waste' after the useful lifetime of a reactor - much like in the fission counterparts).

Nowhere near as much waste as with fissionables, though.
4 / 5 (2) Oct 12, 2012

"Next, the team hopes to attach the device to a larger reactor to see if it can maintain a sufficiently tight magnetic bottle."

Sounds like they're angling to get their handles on ITER
not rated yet Oct 13, 2012
If it could burn p-B11 like the design, there are only a few slow neutrons, from side reactions.
not rated yet Oct 17, 2012
I bet there is enough power in the CT's which encircle the "mug handles" to power the computer equipment that runs the reactor too. Fingers crossed indeed! (fingers raised at OPEC)
1 / 5 (3) Oct 17, 2012
What's really amazing, is that this plasma can be confined and controlled using EM forces, apparently unlike the plasma that constitutes 99.99% of the universe that supposedly is controlled by the remarkably weak (relatively) gravitational force. Weird!
not rated yet Oct 18, 2012
I bet there is enough power in the CT's which encircle the "mug handles" to power the computer equipment that runs the reactor too. Fingers crossed indeed! (fingers raised at OPEC)
With backup power, presumably. Not sure if I like the idea of the computers losing power during a reactor malfunction.
not rated yet Oct 18, 2012
Not sure if I like the idea of the computers losing power during a reactor malfunction.

For a fusion plant that is actually not a problem at all. If you lose confinement the reaction stops on a dime (even if you kept feeding in more fuel)
Fusion reaction require extreme control. Too little fuel, too much fuel, too little confinement...any of these will stop the thing virtually instantly. (and the case of 'too much confinement' isn't possible because the magnets aren't capable of producing that kind of confinement)

Reactor malfunctions during operation would be costly - as you'd have to replace the inner lining of the reaction chamber afterwards. But that's about the extent of the problem.
The worst 'explosive' event that could happen is not a nuclear explosion but a quenching event in a superconductor coil (specifically the resultant flash evaporation of the coolant). While nasty this doesn't pose a risk to anyone not in the same building.
not rated yet Oct 18, 2012
This reminds me of Lee DeForest's first developement of the triode vacuum tube that led to a revolution in electronics that continues to this day. A small current/voltage controlling a much larger one. The vacuum tube voltage amplifiers led proximally to the current amplifying semiconductors, etc. And now we have an analog in plasma control. I LOVE it. Tom Jarboe you old fart tinkerer, one old fart to another, YOU are as they say in Oklahoma, a 'hand'. May you go into the history books as the father of fusion.
not rated yet Oct 18, 2012
May you go into the history books as the father of fusion.

Nope. If you want to go by that kind of 'reasoning' then it's Archimedes (you know: the guy with the lever)

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