# Fusion energy?

1. May 10, 2012

### Hypo

Hallo everyone!

I'd like to understand why is it that the sun can produce fusion energy with less heat then the required heat in our current reactors?

Fusion reactors produce 100M/Degrees to produce a few minutes of fusion where the sun uses only 10M degrees and still produces fusion? Why is that?

Hows is it possibile for us to harness that energy? how will reactors be able to converte that to electricity or any form of energy?

Hyp,

2. May 10, 2012

### tiny-tim

Hallo Hypo!
I think it's the containment problem …

the sun doesn't have any difficulty keeping the stuff in the reactor!

3. May 10, 2012

Staff Emeritus
No, it's a rate problem. The sun takes 10 billion years to use its fuel, i.e. uses 10-10 of its fuel per year. For a fusion reactor, we'd like that number to be tens of percent.

4. May 10, 2012

### Staff: Mentor

With other numbers:
The sun releases about 40W/m^3 of fusion power in the core. The large volume of the sun gives a nice total amount of fusion power. However, for earth, it would mean that 1GWth would require ~25 million cubic meters of plasma. That is a cube with ~300m side length and impractical for power plants.

In addition, the sun has a very high pressure (due to gravity) inside - something which is not reproducible on earth. With the same temperature, the power output would be lower than the sun's by some orders of magnitude.

5. May 12, 2012

### Staff: Mentor

The above answers are all good, however I would like to point out that it boils down to the fact that fusion doesn't start to occur at a specific temperature. Due to quantum effects there is an absolutely tiny chance of two hydrogen atoms fusing together at room temperature. The hotter you get the hydrogen the harder the two collide with one another, which increases the chance that fusion will occur. (Up to a certain point, at which the chance with start to drop again)

Well, first we have to be able to produce a sustained reaction or chain of pulsed reactions that produce more power than they consume. We have to use power to get the magnetic fields, electric currents, and other things that are required to contain and heat the plasma. So figuring out how to do this efficiently is how we achieve fusion power.

As to how we harness this power once we achieve a net gain, there are several options. The simplest is to simply let the neutrons from the reactions heat water and use the steam to power a turbine, like many power plants do today.

Another option, if we can get fusion to work for the particular type of fuel it requires, is to use the actual kinetic energy of the ions after fusion and convert it to electric energy. A moving charge generates a magnetic field and we can use it to slow these ions down and generate a voltage/current in the process.