Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Compact nuclear fusion reactor is 'very likely to work,' studies suggest

nytimes.com

Post reply on HN
Print view View original

71–80 of 373 posts

Re: Compact nuclear fusion reactor is 'very likely to work,' studies suggest

#71

Post by mlindner »

avmich wrote: post #59
tsomctl wrote: post #12

Earlier quoted context omitted.

ITER isn't meant to be a practical design, it's for research. So it's not obsolete just because it's using inefficient magnets.

It could be argued that ITER is actually quite important in learning how to deal with high technical complexity in general. Probably a good reason by itself to keep working on ITER, ISS is way simpler in comparison. https://en.wikipedia.org/wiki/ITER#Criticism "The project however was significantly delayed at the design stage as result of purposeful decision to decentralize its design and manufacturing among 35 parti…

In other words, ITER is a jobs project.

Re: Compact nuclear fusion reactor is 'very likely to work,' studies suggest

#72

Post by mchusma »

jhoechtl wrote: post #52

Honest question: Has man-made nuclear fusion ever happened? Or is it theory, happening on the sun?

Yes man-made nuclear fusion is quite "easy".

The hard part is getting more energy out than you put in.

The sun does this all the time, basically by having so much mass that hydrogen gets sucked in by gravity to collide with other particles. Keeping hydrogen close enough to smash into each other is hard, the sun is just so big that it can do that.

Hydrogen bombs do this by using other explosives to push hydrogen together. This isn't a good power source.

We can't use gravity to cause hydrogen to collide here on earth (we have no artificial gravity). But we have magnets, so we try to bounce hydrogen particles around super fast in a small space with magnets instead of using gravity.

Now getting more energy out is a bit like starting a fire. You need to apply heat for a while with a lighter before the fuel ignites, then the burning fuel keeps releasing energy.

Same basic idea with fusion. You put in energy to start fusing hydrogen. Once the hydrogen is releasing power, it will cause other hydrogen particles to bounce around super fast and continue fusing, releasing more energy.

The part that hasn't really been done yet is proving that the "fire" can stay lit, and that is what people are trying to do. It's hard for a bunch of reasons, but the theme is "making a tiny sun-like place on earth is challenging". When this article mentions "q" that is what it is referring to. q=2 means for every joule of energy put in you get 2 joules out.

(disclaimer: this is a quick version that omits a lot)

Re: Compact nuclear fusion reactor is 'very likely to work,' studies suggest

#73

Post by willis936 »

Someone wrote: post #60
tsomctl wrote: post #12

Earlier quoted context omitted.

ITER isn't meant to be a practical design, it's for research. So it's not obsolete just because it's using inefficient magnets.

The article claims this design can easily be built before ITER is completed (5 years vs 15 years) It also says it can be built much cheaper than the total cost for ITER. The article doesn’t say it, but I would guess that it also can be built for less money than the money needed to complete ITER. If so, what’s not obsolete about ITER? Are there useful experiments that can be done with it that one can’t do with a more…

ITER is much more complicated than SPARC. For example, the disruption mitigation system is similar to DIII-D's but with (I believe) much higher resolution in time and space. ITER has 80 MW of plasma heating but most Q targets only require ~50 MW. It is a platform to do science. It's a huge machine that is meant to demonstrate a tokamak reactor. Corners can't be cut to get there.

Making a tiny machine quickly, skimming over the hard engineering problems is more of a moonshot approach. It's halfway to a startup with actual MIT startups selling HTS coils. Be wary of anyone selling something.

Re: Compact nuclear fusion reactor is 'very likely to work,' studies suggest

#74

Post by ncmncm »

isoprophlex wrote: post #8

I never quite understood the math behind power densities in a fusion reactor. In the sun, isn't energy production occurring at something like 100-1000 W/m3? So, if you want to build a multiple MW fusion plant, shouldn't these plants be ridiculously huge compared to, say, a wind turbine rated at a couple of MW? Is the density of the plasma so much higher in a fusion reactor? Also, something else I never grokked, how d…

Exactly: there is no prospect or intent to actually, ever make a Tokamak that produces useful power. Besides the power density problem and the really absolutely enormous expense and already-sunk cost, the necessary neutrons would destroy the most expensive part of the reactor in short order, and make the rest radioactive.

The whole research program gets its funding as what amounts to a jobs program to keep high-neutron-flux physicists employed and available to draw upon for weapons work. That is one reason why any fusion process that does not emit neutrons is not given any of the research funds: weapons work doesn't need high-alpha-flux physicists. (Secondarily, they have papers that purport to show e.g. p-B fusion could never work.)

If we ever do get practical fusion, it won't be in a Tokamak, it probably won't be on the Earth's surface, and it certainly won't help resolve global climate disruption.

The money being spent on Tokamaks, on the other hand, absolutely could help a great deal with global climate disruption. But not while also maintaining the all-important high-neutron-flux population.

Re: Compact nuclear fusion reactor is 'very likely to work,' studies suggest

#75

Post by JustAPerson »

https://www.youtube.com/watch?v=KkpqA8yG9T4

Here's a video lecture from the MIT Professor (Dennis Whyte) who was leading the research group that provided some of the key designs for the SPARC reactor. As the NYT article explains, that research has been spun out into a startup that raised $200M.

The key breakthrough is the advancement of REBCO tape superconductors which allow you to (1) generate record breaking magnetic field strengths (2) easily disassemble the super conducting loop for fast repairs / refuels / more modular design.

It's a long talk, but it's extremely fascinating. Basically everything becomes much easier once you can increase the magnetic field strength. This talk is fairly accessible to even relative laypeople who have a vague understanding of E&M physics.

Re: Compact nuclear fusion reactor is 'very likely to work,' studies suggest

#76

Post by Already__Taken »

wcarss wrote: post #34
eigenhombre wrote: post #5

Having read about tokamaks for thirty years, I'd be curious what specific breakthroughs and innovations have occurred since the 1980s, which lead to the optimism described in the article (which is otherwise frustratingly devoid of detail). It's great there are seven-peer reviewed articles about SPARC, but plasma was not my specialty in physics -- would any specialists care to comment on whether there is anything part…

My layman's understanding is that recently available (~last 5 years) industrial scale processes to produce rebco tape[1] is the specific advance in superconductor tech that's specifically enabling higher tesla magnetic field strengths from significantly smaller and lighter and easier to manage magnets, so you can get a system that's "powerful enough" to run net posititve at a size that's small enough to be built by a…

2 - skip to ~2:30 for the speaker, whose mic'd and the sound greatly improves.

Good job recording MIT.

Re: Compact nuclear fusion reactor is 'very likely to work,' studies suggest

#77

Post by Baeocystin »

isoprophlex wrote: post #8

I never quite understood the math behind power densities in a fusion reactor. In the sun, isn't energy production occurring at something like 100-1000 W/m3? So, if you want to build a multiple MW fusion plant, shouldn't these plants be ridiculously huge compared to, say, a wind turbine rated at a couple of MW? Is the density of the plasma so much higher in a fusion reactor? Also, something else I never grokked, how d…

>The plasma heats up, but how do you turn that into useful electrical energy?

I appreciate that many people are commenting 'you couple the plasma to a working fluid', but I think the original comment was more along the line of how you couple a confined plasma to a working fluid. By definition the plasma is in a hard vacuum, magnetically bottled. What, then, is the coupling method? Thermal photons escaping confinement? I genuinely have no idea myself, but would really like to know.

Re: Compact nuclear fusion reactor is 'very likely to work,' studies suggest

#78

Post by zachrose »

nielsbot wrote: post #68

My current favorite future fusion reactor project (I'm a layperson) is the Wendelstein 7-X: https://en.wikipedia.org/wiki/Wendelstein_7-X Seems like they're meeting all their planned milestones and it's going well! Excited for their next updates... More from their project page: https://www.ipp.mpg.de/w7x "Wendelstein 7-X is the world’s largest fusion device of the stellarator type."

I’m also a layperson and also a fan of the 7-X, almost on purely aesthetic grounds. The plasma shape is a beautiful twisted loop, the magnets resemble a French crueler, and with the shielding and instrumentation it has all the charm of a steampunk time machine

Re: Compact nuclear fusion reactor is 'very likely to work,' studies suggest

#79

Post by willis936 »

nielsbot wrote: post #68

My current favorite future fusion reactor project (I'm a layperson) is the Wendelstein 7-X: https://en.wikipedia.org/wiki/Wendelstein_7-X Seems like they're meeting all their planned milestones and it's going well! Excited for their next updates... More from their project page: https://www.ipp.mpg.de/w7x "Wendelstein 7-X is the world’s largest fusion device of the stellarator type."

Keep your ear on the floor for a medium-scale HTS stellarator in the US sometime in the next ten years.

https://wistell.engr.wisc.edu

Post reply on HN