Fusion Physicists Found a Way Around a Long-Standing Density Limit (sciencealert.com) 37
alternative_right shares a report from ScienceAlert: At the Experimental Advanced Superconducting Tokamak (EAST), physicists successfully exceeded what is known as the Greenwald limit, a practical density boundary beyond which plasmas tend to violently destabilize, often damaging reactor components. For a long time, the Greenwald limit was accepted as a given and incorporated into fusion reactor engineering. The new work shows that precise control over how the plasma is created and interacts with the reactor walls can push it beyond this limit into what physicists call a 'density-free' regime.
[...] A team led by physicists Ping Zhu of Huazhong University of Science and Technology and Ning Yan of the Chinese Academy of Sciences designed an experiment to take this theory further, based on a simple premise: that the density limit is strongly influenced by the initial plasma-wall interactions as the reactor starts up. In their experiment, the researchers wanted to see if they could deliberately steer the outcome of this interaction. They carefully controlled the pressure of the fuel gas during tokamak startup and added a burst of heating called electron cyclotron resonance heating.
These changes altered how the plasma interacts with the tokamak walls through a cooler plasma boundary, which dramatically reduced the degree to which wall impurities entered the plasma. Under this regime, the researchers were able to reach densities up to about 65 percent higher than the tokamak's Greenwald limit. This doesn't mean that magnetically confined plasmas can now operate with no density limits whatsoever. However, it does show that the Greenwald limit is not a fundamental barrier and that tweaking operational processes could lead to more effective fusion reactors. The findings have been published in Science Advances.
[...] A team led by physicists Ping Zhu of Huazhong University of Science and Technology and Ning Yan of the Chinese Academy of Sciences designed an experiment to take this theory further, based on a simple premise: that the density limit is strongly influenced by the initial plasma-wall interactions as the reactor starts up. In their experiment, the researchers wanted to see if they could deliberately steer the outcome of this interaction. They carefully controlled the pressure of the fuel gas during tokamak startup and added a burst of heating called electron cyclotron resonance heating.
These changes altered how the plasma interacts with the tokamak walls through a cooler plasma boundary, which dramatically reduced the degree to which wall impurities entered the plasma. Under this regime, the researchers were able to reach densities up to about 65 percent higher than the tokamak's Greenwald limit. This doesn't mean that magnetically confined plasmas can now operate with no density limits whatsoever. However, it does show that the Greenwald limit is not a fundamental barrier and that tweaking operational processes could lead to more effective fusion reactors. The findings have been published in Science Advances.
ELI5? (Score:2, Funny)
Re: ELI5? (Score:2, Funny)
Re: ELI5? (Score:5, Informative)
Fusion needs three things to work:
- A âoehighâ density of plasma (high is relative, in reality itâ(TM)s close to a vacuum)
- A high temperature (not relative, literally the hottest things in the solar system)
- A long time at those conditions.
The higher you make the product of those three the more fusion you get and the more energy you get.
At the same time though, you need to stop your fusing stuff from touching the outside of your reactor, because itâ(TM)s incredibly high temperature and radioactivity will destroy the reactor. It will also rapidly cool the reaction, shutting it down. That means you need to be really good at containing the hot plasma in the middle of the reactor.
These reactors do this by using magnets to squeeze the plasma into the middle (increasing the density), and various forms of heating to get to the desired temperatures. However, when you squeeze the plasma, it wriggles around like an eel trying to escape. At some point when you try to grip it too hard, the eel just slips straight out and shoots across the reactor into the walls. That limits the size of the product described at the start, and so limits the amount of power you can get out.
These scientists have discovered that if youâ(TM)re very careful about how you position the eel when you start squeezing you can squeeze a lot harder before it starts wriggling about like crazy.
Re: ELI5? (Score:4, Informative)
Fusion needs three things to work:
- A "high" density of plasma (high is relative, in reality it(TM)'s close to a vacuum) - A high temperature (not relative, literally the hottest things in the solar system) - A long time at those conditions.
This is called the Lawson criterion [wikipedia.org]. And yes, you can offset the last two with more of the first, a higher density allows for lower temperature and a shorter enclosing time.
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Kudos man, this is one of the best ELI5s I've seen.
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Delightful explanation and now forever in my brain fusion will be "squeezing the wriggling eel with magnets"
The first link is clear and accessible (Score:4, Informative)
In summary: you can sustain denser plasma's if you can precisely control the way your plasma is started. That's useful because it helps your reactor reach a break-even point between energy cost (to make, maintain, and contain the plasma) and the amount of energy the plasma emits during its existence.
Fusion is the future ! (Score:2)
Seriously, can ITER use this advance to improve their existing apparatus ?
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If the past is any indication, the answer is no. They'll have to build another multi-billion dollar test apparatus over a decade only to figure out they're still 10 years away from viability. :)
Re: Fusion is the future ! (Score:2)
Unlikely because its magnets suck by modern standards and so it canâ(TM)t reach very high pressures. SPARC/ARC might do it though. And yes, we absolutely will have commercial fusion in 20 years. Likely more like 5-10.
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But most likely not with Tokamak style reactors.
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- Inertial confinement will not work for commercial power generation.
- ITER will plod along through the treacle of bureaucracy and international cooperation, but it will eventually fulfil its purpose and prove the fusion power concept.
- ITER will, however, be overtaken by commercial plants (using its results) before then, but that is fine.
- Embarrassing to say, but I actually do think commercial power generation will happen around 20 years from now
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It could be much earlier than 20 years.
Lets see, I plan to live a bit longer than just 20 more :D
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Commercial outfits will overtake ITER without even bothering to use ITER's results.
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"And yes, we absolutely will have commercial fusion in 20 years. Likely more like 5-10."
We absolutely will not. There may be some test reactors that are energy positive for significant periods of time, but to have solved all the remaining issues AND designed AND built multi megawatt commercial reactors?
Oink flap.
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Check out Helion. They've got an ambitious schedule. Should be interesting to see how well they actually do.
Re: Fusion is the future ! (Score:2)
They have broken ground. SPARC is well under construction. ARC is going to break ground soon. Which is why I said 5-10, not 5.
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Seems like it's the new old buzz word to accompany the power of tomorrow.
On a side note I saw Keanu Reeves was working on a fusion project back in 1996. Maybe that will be commercially available if Morgan Freeman doesn't keep getting in his way. It could be huge!
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It might never happen. As renewables + battery get cheaper, and/or the need for massive AI datacenters dies when IQ growth reaches an asymptote, fusion power production might work but not be economic. But I doubt it.
In from three to eight years, Slashdot will support Unicode.
Your sig checks out
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Amateurs! (Score:2)
Don't hold your breath (Score:2)
Fusion Reactors are Sexy, BUT (Score:2)
I'll wait for this to be reproduced (Score:2)
And small lab environments are not real world results.
I remain skeptical but hopeful.
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I'm afraid YOU are the one who doesn't understand where this was done.
EAST is a small chinese test facility based on a 30 year old design. By today's standards it's lab tool for experimentation no where near the type of environment we see in modern designs. The reactor walls aren't even made of the same materials.
Experimentation like this is encouraging, but it is VERY far from some kind of breakthrough.
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The age of the design has fuckall to do with the findings or relevancy of this specific experiment.
Like I said, you don't know what you're talking about.
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Concise fact filled retort. Well argued. I'm sure everyone reading is now convinced. Well done sir, first class.
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Well-funded American Universities succeed AGAIN (Score:4, Funny)
Sorry, I'm being told and that this breakthrough happened in China and that the current administration completely slashed funding to our universities? That can't be right, that would've set back American research by decades and ceding the advantage to China. I'm gonna have to look into this deeper.
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MIT spun off Commonwealth Fusion years ago. China is late to the party.