Why is nuclear fusion so hard? • Hacker News Board

Re: Why is nuclear fusion so hard?

#141

Post by cjslep » Mon, Dec 10, 2018, 8:12 AM UTC

Animats wrote: post #105

Plasma instability is just awful. See [1]. I thought he was going to go on about some approach to active stabilization of plasmas. But no. There's been work done on that, but it's been years. Anyone following that? Then there's the first wall problem.[2] Fusion generates heat and neutrons. Lots of neutrons, which break atoms apart. Finding something which will stand up to that in an experimental machine has been toug…

Yep, studied Nuclear Engineering at NC State, didn't stick around for the grad program. My friend did, for plasma physics, and is now working at ITER. Plasma confinement is still improving.

Re: Why is nuclear fusion so hard?

#142

Post by thaumasiotes » Mon, Dec 10, 2018, 8:24 AM UTC

sova wrote: post #137

voidmain wrote: post #114

Earlier quoted context omitted.

If you let it cool, it would stop fusing. The fusion power wouldn't magically go up.

fusion halts harmlessly when conditions are unmet

Halting harmlessly is the opposite of "producing a lot more energy".

Re: Why is nuclear fusion so hard?

#143

Post by mathw » Mon, Dec 10, 2018, 8:30 AM UTC

robertsteinhaus wrote: post #139

Mankind is currently in possession of a practical fusion technology. It might be worthwhile to remember that Ivy-Mike fission-fusion technology worked the very first time it was tried in 1952. Mike technology was the basis of the first thermonuclear weapons in the US arsenal. Adapting Mike technology to be pure hybrid DT-DD fusion opens up many new applications in economical power generation. In 60 years, no other fu…

So, how do you turn a bomb into a practical source of power that doesn't destroy the surrounding area the moment you turn it on?

Re: Why is nuclear fusion so hard?

#144

Post by menotyou » Mon, Dec 10, 2018, 10:00 AM UTC

rkagerer wrote: post #91

This is probably another ignorant question, but why can't we "aim" and shoot protons at each other to make them smack together without requiring all that heat and pressure?

Like hydrogen-boron fusion?

https://newsroom.unsw.edu.au/news/science-tech/laser-boron-f...

https://revolution-green.com/breakthroughs-make-commercial-l...

Other: Google for "LENR". Some people claiming (for years) they are near to success.

Re: Why is nuclear fusion so hard?

#145

Post by throwaway77384 » Mon, Dec 10, 2018, 11:09 AM UTC

dukoid wrote: post #15

If you understand German, trust me and listen to this podcast about Wendelstein 7-X O:) : https://alternativlos.org/36/

Almost trotted this one out myself. So good!

Re: Why is nuclear fusion so hard?

#146

Post by kungtotte » Mon, Dec 10, 2018, 11:11 AM UTC

sethrin wrote: post #135

narag wrote: post #112

Earlier quoted context omitted.

Nuclear tech is not even a century old. The idea that we can't do any better in a thousand or a million years seems so improbable to me that I can't take it seriously. There is some kind of extrange pessimism around that mindset: that we will be extinct much sooner, or that the Sun will die and thus Humanity, as if there's no obvious way to escape that apocalypsis.

I don't know what it is about the idea of the far future that makes people so willing to throw out fundamental physical laws. The relevant point here would be that there are fundamental limits to heat transfer, and a finite amount of work which can be done on Earth-as-we-know-it for a given unit of time, irrespective of the energy source. An "unlimited" source of energy would be in practice limited by its heat output…

Improbable is not the same as impossible. We didn't even know about atoms for a huge stretch of science, and now we're smashing them together to break them apart looking for smaller things.

Is it completely out of the question that some discovery will be made that invalidates our current understanding of physics?

Re: Why is nuclear fusion so hard?

#147

Post by pfdietz » Mon, Dec 10, 2018, 12:45 PM UTC

ravar wrote: post #123

bjelkeman-again wrote: post #122

Earlier quoted context omitted.

Could that be explained with less jargon? I’d like to understand it.

There is a chain of individual steps that need to happen to create the final product of hydrogen fusion, helium. One of the crucial steps is the production of deuterium from two protons. This step is incredibly slow and limits the rest of the chain. However if you skip the slow step and start by fusing deuterium and tritium you can have a much faster and efficient reactor.

Indeed. After a D nucleus forms in the sun, it reacts (with a proton, to form 3He and a photon) within a few seconds.

The 3He+3He reaction is also slow, but not as slow as that first step.

Re: Why is nuclear fusion so hard?

#148

Post by pfdietz » Mon, Dec 10, 2018, 12:48 PM UTC

thomasahle wrote: post #107

mannykannot wrote: post #41

This is somewhat tangential to the specific issue here, but I was surprised by this: At the center of the Sun, fusion power is estimated by models to be about 276.5 watts/m3. Despite its intense temperature, the peak power generating density of the core overall is similar to an active compost heap, and is lower than the power density produced by the metabolism of an adult human.[1] So practical fusion power requires…

It continues like this though: > The low power outputs occurring inside the fusion core of the Sun may also be surprising, considering the large power which might be predicted by a simple application of the Stefan–Boltzmann law for temperatures of 10 to 15 million kelvins. However, layers of the Sun are radiating to outer layers only slightly lower in temperature, and it is this difference in radiation powers between…

> So if a m^3 of sun core was moved to a powerplant it would generate a lot more energy.

Yes, for a tiny fraction of a second as it exploded. Its pressure would far beyond what any material could withstand (and magnetic confinement does that change that, as the outward pressure has to eventually be carried by the magnet support structure).

Re: Why is nuclear fusion so hard?

#149

Post by pfdietz » Mon, Dec 10, 2018, 12:51 PM UTC

robertsteinhaus wrote: post #139

Mankind is currently in possession of a practical fusion technology. It might be worthwhile to remember that Ivy-Mike fission-fusion technology worked the very first time it was tried in 1952. Mike technology was the basis of the first thermonuclear weapons in the US arsenal. Adapting Mike technology to be pure hybrid DT-DD fusion opens up many new applications in economical power generation. In 60 years, no other fu…

They looked at this. It's grossly uneconomical as a power source.

"In a 1975 review of the various Plowshares efforts, the Gulf University Research Consortium (GURC) considered the economics of the PACER concept. They demonstrated that the cost of the nuclear explosives would be the equivalent of fuelling a conventional light-water reactor with uranium fuel at a price of $328 per pound."

Re: Why is nuclear fusion so hard?

#150

Post by BurnGpuBurn » Mon, Dec 10, 2018, 12:53 PM UTC

mdpopescu wrote: post #115

aurizon wrote: post #93

Here is a thought experiment( no cats harmed or wetted). Show a cat how the toilet flushes, then try to flush the cat. You have two hands, the cat has 4 paws, with sharp claws as well as teeth. This will give you an idea.... Stars have gravity and mass- we do not, so we must try and compress the plasma, heat it AND stops the paws from grabbing the exterior. In truth magnetic confinement is a poor way to constrain a p…

Controlled fusion has always been 5 to 10 years away, just as we've always been at war with Eurasia.

I remember distinctly reading a popular science magazine article when I was young (it had that great plasma picture with all the plasma arcs fizzing over the floor of a giant lab) that stated that we could have fusion power plants in 25 to 50 years. That was 30 years ago.