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Chinese Tokamak reaches over 100M degrees

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Re: Chinese Tokamak reaches over 100M degrees

#31

Post by NamTaf »

piannucci wrote: post #17
saagarjha wrote: post #12

Earlier quoted context omitted.

Except Wikipedia seems to put the barrier significantly higher, at 100 keV: https://en.m.wikipedia.org/wiki/Thermonuclear_fusion#Tempera...

A system of particles in thermal equilibrium will contain a small fraction whose kinetic energy exceeds the average by a factor of 10. Also, the energy available in the center-of-mass frame of two colliding particles is higher if they happen to be moving in opposite directions. That could give you another factor of up to 2. In any event, I don't think you want your fuel fusing all at once!

Expanding on this, this 10KeV temperature is the average of all particles, and there's a distribution around this average. Some will be higher, and thus more capable of colliding with high energy.

In addition to that, whether two nuclei fuse is also dependent on how squarely they collide. A glancing blow intuitively allows both nuclei to push each other away a lot easier than if they experience a head-on collision.

A graph of the fusion rate such as [1] shows that even at much lower average temperatures, fusion will occasionally happen when two higher-than-average nuclei collide head-on. As the temperature gets higher, this rate increases as more particles have enough energy and less require those head-on collisions. The peak rate for D-T according to this graph is about 70kEv.

I can't speak to why the grandparent's link referenced 100kEv, as it's been a decade since I last studied this and I'm very rusty.

[1]: https://en.wikipedia.org/wiki/File:Fusion_rxnrate.svg

Re: Chinese Tokamak reaches over 100M degrees

#32

Post by adtac »

Once we achieve sustainable fusion, will it be possible to "share" the energy with everyone else to create more independent fusions? Kinda like keeping the candle burning so as to light more candles because matches are too costly.

Now, I don't expect politics to allow sharing of fusion energy to help other countries.

Re: Chinese Tokamak reaches over 100M degrees

#33

Post by hoffs »

adtac wrote: post #32

Once we achieve sustainable fusion, will it be possible to "share" the energy with everyone else to create more independent fusions? Kinda like keeping the candle burning so as to light more candles because matches are too costly. Now, I don't expect politics to allow sharing of fusion energy to help other countries.

Isn't fusion reactor basically infinite energy, I mean sure it makes total sense to no share it with other because you can sell your free energy for cash, but considering that a lot of global scientists work on it and most of the findings are published, don't think that such strategy would last long.

Re: Chinese Tokamak reaches over 100M degrees

#34

Post by kungtotte »

docker_up wrote: post #11

Stories like this scare me. With all of the precautions, even things like Fukushima failed and will poison our ocean for millennia. What happens if we have a runaway fusion process through some pathway that was unexpected? With all the talk about the LHC possibly producing mini blackholes or magnetic monopoles that could potentially cause protons to decay spontaneously, I don't have enough nuclear physics background…

The earthquake was the most powerful to ever hit Japan and the fourth most powerful in the world since modern record keeping began, and the investigation into the disaster showed that the safety precautions weren't adequate in the first place.

You can't dismiss the technology based on that incident. Just like we don't ban cars because a lot of people don't operate them properly.

Re: Chinese Tokamak reaches over 100M degrees

#35

Post by throwaway_se099 »

Quenty wrote: post #19
docker_up wrote: post #11

Stories like this scare me. With all of the precautions, even things like Fukushima failed and will poison our ocean for millennia. What happens if we have a runaway fusion process through some pathway that was unexpected? With all the talk about the LHC possibly producing mini blackholes or magnetic monopoles that could potentially cause protons to decay spontaneously, I don't have enough nuclear physics background…

Fusion is not a chain reaction. The energy maintained for this is incredible and it can’t run away. Fusion has no toxic or radioactive bioproducts. As a power source fusion is pretty good, which is why it’s such a target for research. See: http://www.fusenet.eu/node/38

> Fusion has no toxic or radioactive bioproducts.

D-T fusion, which is the easiest to achieve and perhaps sustain, directly produces He nuclei (that is, alpha particles) and rather energetic neutrons at 14 MeV. Those neutrons, aside from being a form of ionizing radiation themselves, are bound to transmute some of the surrounding material into radioactive isotopes. So, I don't think that "no toxic or radioactive byproducts" is correct. However, the results are easier to handle than those of fission reactors.

Re: Chinese Tokamak reaches over 100M degrees

#36

Post by _nalply »

Quenty wrote: post #19
docker_up wrote: post #11

Stories like this scare me. With all of the precautions, even things like Fukushima failed and will poison our ocean for millennia. What happens if we have a runaway fusion process through some pathway that was unexpected? With all the talk about the LHC possibly producing mini blackholes or magnetic monopoles that could potentially cause protons to decay spontaneously, I don't have enough nuclear physics background…

Fusion is not a chain reaction. The energy maintained for this is incredible and it can’t run away. Fusion has no toxic or radioactive bioproducts. As a power source fusion is pretty good, which is why it’s such a target for research. See: http://www.fusenet.eu/node/38

I don't know a lot about fusion, however «no radioactive bioproducts» seems to be off. I just read Wikipedia, and the deuterium-tritium reaction produces neutrons. Radiation seems to be not as bad as for fission reactions, however it is NOT radiation-free.

Re: Chinese Tokamak reaches over 100M degrees

#37

Post by afraca »

i_am_proteus wrote: post #27
agoldis wrote: post #5

Okay, did some search: - When two hydrogen nuclei combine, they produce an enormous amount of energy. That process is known as nuclear fusion. - Light nuclei have to be heated to extremely high temperature, it is challenging to create a controlled, safe fusion reactor that offers more energy than it consumes. Once we have such we’d have a near-limitless source of clean energy. - Nuclear fusion does produce radioactiv…

I will add: - While the products of the fusion reaction are short-lived, operating a fusion reactor will active materials in the reactor and create some longer-lived radioisotopes. - Unlike a fission reactor, which is loaded with months to years worth of fuel, a fusion reactor would have fuel constantly injected. So operator action to stop injecting fuel would stop the nuclear reaction.

Can either you or your parent poster say what "short lived" and "longer-lived" would be roughly?

Re: Chinese Tokamak reaches over 100M degrees

#38

Post by Arnt »

adtac wrote: post #32

Once we achieve sustainable fusion, will it be possible to "share" the energy with everyone else to create more independent fusions? Kinda like keeping the candle burning so as to light more candles because matches are too costly. Now, I don't expect politics to allow sharing of fusion energy to help other countries.

No, it's not. The gear necessary to maintain controlled fusion is not portable.

Re: Chinese Tokamak reaches over 100M degrees

#39

Post by aaaaaaaaaab »

adtac wrote: post #32

Once we achieve sustainable fusion, will it be possible to "share" the energy with everyone else to create more independent fusions? Kinda like keeping the candle burning so as to light more candles because matches are too costly. Now, I don't expect politics to allow sharing of fusion energy to help other countries.

What... no. Igniting fusion is easy. Keeping the plasma confined is the hard part due to its immense heat.

Re: Chinese Tokamak reaches over 100M degrees

#40

Post by thaumasiotes »

NamTaf wrote: post #8
daxfohl wrote: post #6

Earlier quoted context omitted.

What important happens at that temperature?

As I understand, this represents sufficient energy to overcome the Coulomb Barrier [1] which naturally repels atoms apart. To cause fusion, you need to push particles together either hard enough or fast enough that they push through this repulsion and fuse. The repulsion is a product of the electrostatic repulsion of the positive charges of the nuclei (pushing the positive ends of two magnets together, essentially).…

> you need to push particles together either hard enough or fast enough that they push through this repulsion

What's the difference between "hard" and "fast"? What does pushing "hard" mean?

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