Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: thedoc on 09/09/2016 10:23:02
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Eric Sorensen asked the Naked Scientists:
Hello Naked Scientists!
I understand that the primary focus in nuclear fusion research is on deuterium-tritium or deuterium-helium-3 reactions, because they yield more output energy and require less input energy than other reactions. However, since the fuel is so rare, why does it seem like there is no focus on using proton-proton fusion, which could work using simple hydrogen? Also, might it ever be possible to generate power with fusion from *any* isotope (up to iron)?
Thanks, and keep up the great work!
What do you think?
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The proton-proton reaction is possible, but it is very inefficient, because when two protons collide, they form Helium 2 which is very unstable, and immediately disintegrates back into 2 protons.
The proton-proton reaction can only progress in the extremely rare case where one of the protons interacts with an electron in the plasma to form a neutron (forming stable Deuterium) before the Helium 2 disintegrates. Nuclear interactions between protons and electrons are governed by the Weak Nuclear Force, and occur very rarely.
By extracting deuterium from seawater, this very inefficient proton-proton step is bypassed, allowing fusion to occur much more quickly. Interactions between Deuterium nuclei occur via the Strong Nuclear Force, which occur much more rapidly than interactions via the Weak Nuclear Force. (Or it would, if we could get controlled fusion to work at all!)
The Deuterium-Tritium reaction occurs at an even lower temperatures than Deuterium-Deuterium, which makes it useful to investigate, despite the nuisance of having to generate and handle the radioactive Tritium.
See: https://en.wikipedia.org/wiki/Proton%E2%80%93proton_chain_reaction
https://en.wikipedia.org/wiki/Fusion_power#Fuels
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It works in stars but requires temperatures of 15*10^6 °K and volume for volume produces about as much power as a manure heap
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It works in stars but requires temperatures of 15*10^6 °K and volume for volume produces about as much power as a manure heap
I think that may be mass for mass, rather than volume for volume.
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It works in stars but requires temperatures of 15*10^6 °K and volume for volume produces about as much power as a manure heap
I think that may be mass for mass, rather than volume for volume.
Dunno about that, since the sun, where such conditions allow proton-proton reactions to exist, is around twice the density of manure. About 1.3x manure on average, but the such reactions don't much take place in the outer low-density regions.
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Fair enough; it makes much less difference than I thought.