> 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 :)
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 :)