why can"t humans harness nuclear fusion but only nuclear fission?

Answer 1

We have harnessed nuclear fusion--in weapons.

The tough thing (for fusion energy production) is controlling a sustained reaction because the plasmas involved are so hot and energetic. Plasma scientists have been working hard for many years to contain them inertially or magnetically and actually get out more energy than they put into the effort. No luck so far (incremental progress maybe), but there may be hope on the horizon (or so they claim to get funding for their projects). France is working on a big machine that might be the first large scale demo.

Answer 2

I assume you mean harness for energy production (as opposed to city destruction). Controlled fusion for such purposes requires confining an extremely hot plasma of sufficient density and for a sufficiently long time to liberate more fusion energy than the energy that must be invested to created and confine the plasma in the first place. This has only been done to date by using a fission bomb as the primary energy source. Fission bombs only work with a minimum critical mass, which releases a minimum energy that's a bit hard on the turbines.

Answer 3

Nuclear fusion takes place in a plasma state. Plasma is a unique form of matter consisting of a super-heated ionised gas which is extremely hard to contain. The only way to do so is to use magnetic fields. Scientists and engineers are currently getting there.

We are approaching a break-even point with nuclear fusion, where the energy we can extract is comparable with the energy we use in creating the fusion. Once we pass through this point, and have improved containment systems, then fusion will be possible.

Answer 4

Because nuclear fusion requires alot of energy to force nuclei to bind together and produce fusion reactions.

Answer 5

Fusion reactions generally occur at temperatures of 90,000,000 °F (50,000,000 °C) or greater; hydrogen atoms at even higher temperarures. That makes fusion reactions impractical. Maybe some day they can work around that.

Answer 6

Um, yes we can. It's called the hydrogen bomb. An immense amount of heat is used to cause an exothermic reaction by fusing hydrogen atoms to create Helium. God, that was a dumb question.