[VladRussian2]

> It may in fact not be possible to do better-than-breakeven fusion on a small (relative to a star) scale.

the H-bomb is better-than-breakeven and much smaller than star scale. What you say may be true for Tokamak like confinement schemes whereis H-bomb is inertial confinement, and it works. And it is pretty clear that inertial confinement in several orders of magnitude smaller scale than H-bomb would work too. Look at Sandia Z-machine - an order of magnitude up, and it would get breakeven. Not that anybody really needs it :)

[arethuza]

JET (Joint European Torus) achieved a Q of 0.7 - with break-even being defined as a Q of 1:

http://en.wikipedia.org/wiki/Joint_European_Torus

ITER is aiming for a Q of 5 for 480 seconds:

http://en.wikipedia.org/wiki/ITER

[lisper]

OK, let me be more precise: it may not be possible to do better-than-breakeven fusion on a small scale in a way that makes the resulting energy safely harnessable for useful work.