German Physicists Reach Milestone In Nuclear Fusion Energy Quest

[muriel_volestrangler]

A German nuclear fusion experiment has produced a special super-hot gas which scientists hope will eventually lead to clean, cheap energy.

The helium plasma - a cloud of loose, charged particles - lasted just a tenth of a second and was about one million degrees Celsius.

It was hailed as a breakthrough for the Max Planck Institute's stellarator - a chamber whose design differs from the tokamak fusion devices used elsewhere.
...
The team at Greifswald, in northeastern Germany, aim in future to heat hydrogen nuclei to about 100 million C - the necessary conditions for fusion to take place like in the Sun's interior. They will use deuterium, a heavier type, or isotope, of the element.

The stellarator's plasma was created on Thursday using a microwave laser, a complex combination of magnets and just 10mg of helium. The Max Planck Institute calls its machine Wendelstein 7-X.

http://www.bbc.co.uk/news/world-europe-35074848

[longship]

1. One has to use deuterium.

Ordinary hydrogen has no neutron with which to make helium, which requires two of them. Deuterium has the required neutron in its nucleus.

[muriel_volestrangler]

2. Deuterium is relatively easy to concentrate, though

There's a certain amount of it in all water. It's tritium or helium-3 that are the exotic fusion fuels - you need a nuclear fission reactor, or to go to the moon for the latter.

[longship]

3. Yup!

But normal hydrogen is basically useless for fusion. That was my point. Sorry that I did not make that clear. The wording in the article is a bit confusing about that.

[thereismore]

4. 3H, not 3He. nt

[jakeXT]

5. It both works, one reaction throws away a neutron, the other reaction throws away a proton

[thereismore]

6. Nice, thanks. nt

[Angleae]

7. Elemental helium has no neutrons.

Helium-4 has 2 neutrons. When 2 hydrogen atoms are fused together you get pure helium, whey you fuse 2 deuterium atoms together you get helium-4.

[longship]

8. AFAIK, almost all helium has 2 neutrons.

Helium nucleus would not be stable without neutrons. There is no Helium-2 in nature, as far as I know.

I may be wrong on this, but I highly doubt it.

[Angleae]

9. On earth yes. In space no.

Nearly all deuterium is left over from the big bang. Stars are using pure hydrogen in their fusion cores.

[longship]

10. Helium-2 is extremely unstable.

Last edited Thu Dec 17, 2015, 02:56 PM - Edit history (3)

It has negative binding energy. It immediately changes to an atom of deuterium via beta-plus decay.

The effective transformation is this:

H1 + H1 -> D2 + e+ + nu + 0.42 MeV

(Sorry, don't know how to type Greek. nu is the electron neutrino. e+ is the positron, D2 is deuterium, heavy hydrogen.)

So, no. Helium-2 is not found in nature. It is only seen in the cores of main sequence stars as part of the fusion process that generates He-4. It is only there as a step which inevitably and instantly leads to Deuterium, which subsequently fuses to He-4.

So I will stand by my posts.

[Treant]

11. Beta decay takes care of that.

Usually, in a basic small stellar core (Sun sized or smaller), two hydrogen (simple protons) bang together and fall apart very quickly. Diproton (helium-2) is incredibly unstable. This happens most of the time, with no net energy absorbed or released.

Rarely, one of the protons decays to a neutron, and the diproton becomes deuterium. That's then free to fuse with another hydrogen atom to produce helium-3. Two helium-3 atoms will then fuse to form a helium-4, and release two hydrogen atoms again as well.

That happens often enough to maintain hydrostatic equilibrium of the star. If it didn't, pressures and temperatures would increase until enough diproton had the chance to decay and release enough energy to do so.

Larger stellar cores (just a tiny bit more massive than our Sun and upward) use the CNO (carbon, nitrogen, and oxygen) process primarily instead.