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Why is nuclear fusion so hard?

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Re: Why is nuclear fusion so hard?

#111

Post by thaumasiotes »

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.

Would it? Or would it expand into basically normal hydrogen and helium?

Re: Why is nuclear fusion so hard?

#112

Post by narag »

simonh wrote: post #96
kamaal wrote: post #53

Earlier quoted context omitted.

Is this an another way of saying that the only way to fuse to Hydrogen is to create a structure as large and with gravitational features that of a star? Then a star/solar energy is the only way you will ever have large scale fusion energy generation and harvesting.

I suppose the universe doesn't owe us a cheap, easy, unlimited source of energy. A lot of people seem to think that it's inevitable we will achieve amazing, magical feats of technology given sufficient time and effort that are unthinkable today. Maybe. But it's also just as possible that we already know most of the general parameters of what is possible in the universe, and the peak practical feats of technology that…

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.

Re: Why is nuclear fusion so hard?

#113

Post by sova »

thaumasiotes wrote: post #111
thomasahle wrote: post #107

Earlier quoted context omitted.

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. Would it? Or would it expand into basically normal hydrogen and helium?

Provided you could keep the plasma contained in magnetic fields, it would certainly generate plenty of free neutrons to provide heat for substantial power generation.

Re: Why is nuclear fusion so hard?

#114

Post by voidmain »

sova wrote: post #113
thaumasiotes wrote: post #111

Earlier quoted context omitted.

> So if a m^3 of sun core was moved to a powerplant it would generate a lot more energy. Would it? Or would it expand into basically normal hydrogen and helium?

Provided you could keep the plasma contained in magnetic fields, it would certainly generate plenty of free neutrons to provide heat for substantial power generation.

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

Re: Why is nuclear fusion so hard?

#115

Post by mdpopescu »

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.

Re: Why is nuclear fusion so hard?

#116

Post by User23 »

intralizee wrote: post #36
oblio wrote: post #32

Earlier quoted context omitted.

Why do you need it to be legalized? After all, it's a one way trip, you don't care about being convicted post mortem, do you? :)

Statistically failure rate is high and where the very real outcome of brain damage is possible. Wouldn’t want to be stuck in a state causing more resources spent and unable to attempt the act again. I am seeking it medically for the record and I assume most people are just irrational against letting people die which is why this world is in jeopardy anyway.

Interestingly and sadly a rather bright young man set his mind to exactly this problem and engineered a solution. https://imgur.com/a/Z5mEB#0bVIYlf

Re: Why is nuclear fusion so hard?

#117

Post by ScottBurson »

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…

Not exactly. If, using your Star Trek-style transporter, you instantaneously transported a cubic meter of sun core into empty space, it would radiate a lot of power at first, but by the very fact of radiating all that power, it would quickly cool, especially if you didn't have a good way of keeping it from expanding. But even if you did have some way to contain it, it would still cool pretty fast, since it would no longer be receiving the power input of all the other core stuff around it.

Re: Why is nuclear fusion so hard?

#118

Post by peterashford »

narag wrote: post #112
simonh wrote: post #96

Earlier quoted context omitted.

I suppose the universe doesn't owe us a cheap, easy, unlimited source of energy. A lot of people seem to think that it's inevitable we will achieve amazing, magical feats of technology given sufficient time and effort that are unthinkable today. Maybe. But it's also just as possible that we already know most of the general parameters of what is possible in the universe, and the peak practical feats of technology that…

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 think that significant swathes of human kind throughout history have assumed that their current state of existence is the peak and final form of humanity. While it is always logically possible that this is the case, it has never yet been true.

Re: Why is nuclear fusion so hard?

#119

Post by hobscoop »

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?

Say you shoot the deuterium and tritium ions at each other in beams. Making two ions fuse isn't quite the same as hitting a fixed bullseye. Typically, physicists consider a 'cross section' for a reaction between two particles as a function of their relative velocity: a notional area that allows one to compute the probability of a reaction occurring, which may be thousands of times larger or smaller than what we typically think of as the physical size of the particles.

The cross sections for fusion reactions are significantly less than 1000th those of elastically bouncing off, even at the optimal velocities. Fusion reactions release about 1000 times[2] the typical energy needed by the reactants in order to get close enough for there to be any significant probability of reaction. So a one-pass beam system is always going to lose out to elastic scattering.

[1] https://en.wikipedia.org/wiki/Nuclear_cross_section [2] D + T releases 17.6 MeV of energy; typical fuel temperatures are 15 keV.

Re: Why is nuclear fusion so hard?

#120

Post by rectangletangle »

narag wrote: post #112
simonh wrote: post #96

Earlier quoted context omitted.

I suppose the universe doesn't owe us a cheap, easy, unlimited source of energy. A lot of people seem to think that it's inevitable we will achieve amazing, magical feats of technology given sufficient time and effort that are unthinkable today. Maybe. But it's also just as possible that we already know most of the general parameters of what is possible in the universe, and the peak practical feats of technology that…

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.

Agreed, the accepted models in physics are laughably incomplete. There is still a tremendous amount we still don't know. Although it's possible we've peaked, I have doubts.

It is also a self fulfilling prophecy to declare that we have reached our technological apex, and not striving to progress further.

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