Energy

Nuclear fusion plasma could be stabilized against large eruptions – by causing lots of small ones

Nuclear fusion plasma could be...
The researchers conducted the experiments in the DIII-D tokamak in San Diego
The researchers conducted the experiments in the DIII-D tokamak in San Diego
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The researchers conducted the experiments in the DIII-D tokamak in San Diego
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The researchers conducted the experiments in the DIII-D tokamak in San Diego

As the Sun and stars themselves can attest, nuclear fusion could be an essentially unlimited energy source, if we can only harness it. The problem is that the plasma used is inherently unstable, and large eruptions can damage the reactors containing it. But now, physicists from the Princeton Plasma Physics Laboratory (PPPL) have found a way to prevent those large eruptions, by triggering lots of small ones through the injection of tiny pellets of beryllium.

Nuclear fusion is basically the opposite of nuclear fission, which is the method used in nuclear power plants around the world. Where fission involves splitting atoms and collecting the energy released, fusion is all about merging the nuclei of atoms together, which is cleaner, safer and more efficient than fission.

This is usually done in hollow, donut-shaped reactors called tokamaks, which are filled with rings of plasma as hot as the Sun. But as you'd expect, it takes tremendous effort to maintain the intense pressures and temperatures required for an "artificial star" here on Earth. Eruptions called edge-localized modes (ELMs) can damage the walls of reactors, making them less secure and requiring the replacement of parts far too regularly.

ELMs are hard to eliminate, but as the PPPL researchers wondered, maybe they can be controlled instead. The team found that creating a series of small ELMs could prevent larger, more damaging ones from occurring. These smaller eruptions could be triggered by injecting pellets of beryllium into the boiling plasma at regular intervals. The team was testing whether the technique could be used in ITER, a tokamak currently being constructed in France.

Computer simulations showed that granules of beryllium, measuring about 1.5 mm thick, could get deep enough into the plasma to trigger ELMs most effectively. Next, the team ran physical experiments in the DIII-D, a tokamak reactor housed in the National Fusion Facility in San Diego.

The researchers used magnetic fields to constrain the plasma in the same way ITER will, and injected granules of carbon, lithium and boron carbide, which are all light metals with similar properties to beryllium. And the first results appear successful.

"This is the first attempt to try to figure out how these impurity pellets would penetrate into ITER and whether you would make enough of a change in temperature, density, and pressure to trigger an ELM," says Rajesh Maingi, co-author of the study. "And it does look in fact like this granule injection technique with these elements would be helpful."

The team says that beryllium pellets could be one of many plasma-management tools put to use in tokamaks, with others including external magnets and deuterium pellet injections. The next step is to test the technique out on other tokamaks, like the Joint European Torus (JET) in the UK.

The research was published in the journal Nuclear Materials and Energy.

Source: PPPL

8 comments
Mr T
40 years and at least 100 billion dollars and we still don't have fusion generators. Time to give it up, it's a bad idea, sink any future fusion money into renewables instead, you will get a much better return...
Brian M
@MrT
You could argue the same logic at finding a cure for cancer - not there yet but progress is being made.
Its a balance about the amount spent versus the possible returns - which would have massive implications to what we can do.
Its not just about commercialising controlled fusion but also about learning more on physics and engineering.
Mike_S
@Mr T: It's September 1879. You say to Thomas Edison "Give up, you have tried 98 times, your electric bulb is not going to work, better concentrate on improving kerosene lamp". And today you would be sitting in your kerosene burn smelly living room every night. Great advise!
fb36
IMHO, all research into fusion power generation is absolutely worth it, because fusion power can allow humanity do revolutionary advancements (which are absolutely cannot be done using solar & wind power etc, because they all would be too feeble for such purposes)!!!
Like what???
How about doing seawater desalination @ global scale & using a global clean water pipeline to provide water to everywhere on Earth??? (So no more droughts & any/all lands can be used for agriculture or forests etc.)
How about producing titanium (which is plenty to mine but requires so much electricity) @ global scale & making all kinds of vehicles (land/sea/air) & even whole cities from titanium (which is light & strong & durable)!!!
Lance
I pity the fool.
Fletcher
@Mr T Because of the money already spent we now have reactors that have broke the input in vs output out point (it's just not profitable yet.) But personally I see no greater advancement on mankind's horizon than making fusion energy commonplace. Once that happens we will truly be able to leap to deep space travel and colonization. Besides if we didn't spend this money on research what would it have been spent on, weapons?
Fastestrigger
Im really hoping to see this accomplished. Once we harness this type of energy things like space travel and space probes will be able to go even further. With the benefits of fusion power we can eliminate a lot of other energy sources .
Kpar
The real problem with fusion power is the conversion of the released energy to a useful form- electricity.

These fusion reactors all are basically steam engines, and they extract the energy by heating (stainless steel) cooling jackets filled with water, which then power steam turbines to generate the electricity.

The problem? Fast neutron flux causes blistering, spalling, and brittleness of the steel, requiring its periodic replacement- and that steel is now HIGHLY radioactive. Storage of this very dangerous material is now required, and it could be many megatons of waste- even more than the radioactive "ash" from a fission reactor.