Reply To: NEW ANIMATIONS

[Ivy Matt]

It’s my understanding that the fusion energy gain factor (Q) is what is also known sometimes as “scientific break-even”, and compares an input of electrical energy to an output of fusion energy in the form of kinetic energy of particles or electromagnetic radiation. So, in order to power itself, a fusion reactor running at a Q of 1 would need to convert the fusion energy back to electricity with 100% efficiency, which is impossible. Although Q = 1 would be a big scientific breakthrough, a fusion reactor that generates electricity would have to have a Q of greater than 1 to power itself, let alone to produce surplus electricity. A Q of 20 is about what is needed for a practical tokamak reactor.

Regarding JET’s Q of 0.75, if you check the fusor.net thread Steven Sesselmann linked to, you’ll find Richard Hull’s criticism of JET’s energy accounting in his June 4, 2008 comment. Apparently they counted the energy required to heat the plasma, but not that used to produce the magnetic fields, run the vacuum pumps, etc. The point is that an economical reactor design would need to take these things into account. Not to discourage anyone too much, but I suppose you could compare it to the difference between breaking the sound barrier and producing an economical supersonic airliner.

The p+B11 reaction doesn’t really change the accounting of the output energy, which is still in the form of kinetic energy of particles and electromagnetic radiation. What it does change is the way that output energy could be converted back into electrical energy. Charged particles (p+B11) and neutral particles (D+D, D+T) are converted to electricity using different methods, and the method (direct conversion) for charged particles is expected to be considerably more efficient than the method (steam turbines) for neutral particles. That said, any reactor that uses the D+T or D+D reactions also produces some charged particles as well as electromagnetic radiation, and direct conversion was originally posited as a method to obtain additional electrical energy from such reactions. However, it’s my understanding that in conventional tokamak designs the charged particles are intended to recirculate to keep heating the fusion plasma, which would preclude them being used for direct conversion. As for electromagnetic radiation…I’d love to see a tokamak + “onion” reactor design. That would certainly be interesting.