What is the Most Efficient Fuel for Fusion Reactors: T-D, D-D, or D+He-3?

[Basil Currie]

Hi,
Does a T-D or a D-D fusion release more energy? Even if D-D needs higher temperatures, would it produce more energy in a fusion reactor?

 

[mfb]

These are numbers you can easily look up. DT wins by a big margin.

 

[Javier Lopez]

In one way the deuterium tritium fusion generates 17.6MeV
D+T=2He4+n +17.6MeV

In the other way the D+D fusion is more complex:
D+D->T+p +4.03MeV (a 50% of the reactions)
D+D->He3+n +3.27MeV (a 50% of the reactions)
But tritium fuses very quickly with deuterons as cross section is much larger than D+D fusion and D+T generates 17.6MeV as said before
Also happens with the Helium-3 that fuses again more easily with deuterons giving 18.3MeV, so if the reactor fuses also helium-3 at the end you should have:
D+D+D->He4+n+p+ (4.03+17.6)*50%
D+D+D->n+p+He4+ (3.27+18.3)*50%
So:
D+D+D->He+n+p+21.6MeV

So D+D =2/3*21.6MeV=14.4MeV that is less than 17.6MeV.
But that is not the exact account as long as Tritium does not exists so it is generated using the generated neutron again lithium target to generate tritium releasing more energy that I did not took in account

 

[mfb]

D+He-3 needs even higher temperatures for a relevant cross section than D+D.
If you don't need tritium as fuel you can use the neutrons for some exothermic reactions - even fission has been proposed (fusion-fission hybrid).