[dr_lew]

First, the efficiency of a particular reaction is entirely a function of nuclear reaction kinetics, so, you hit the temperature and pressure necessary to overcome the activation energy and you're good to go, regardless of whether that takes you a few nanoseconds or a few million years. It took a long time to get there in the sun because gravity is weak, and gravitational collapse takes a long time. But, once you get there, you're there. With lasers doing the inertial confinement you can get to temperature and pressure much faster.

We're comparing steady state conditions over some period of time. The tens of millions of years I cited represents the length of time that the sun could shine on its energy of gravitational contraction, and I'm counting this total energy as the ( non-nuclear) ignition energy. So it takes that long for the sun to "break even" with radiation presumed to originate from fusion. So that's its break even confinement time.

With inertial confinement, the laser blast inputs a certain energy, and the confinement must be long enough so that the fusion reaction generates an equal amount of energy.

Well ... I guess this makes for a difficult comparison, since the laser energy input ( presumed instantaneous ) is arbitrary, whereas the sun's gravitational self-energy is a function of its mass and radius. It follows that my inference that the P-T conditions must "greatly" exceed the solar center had no basis. So I was RRRRRR .... RRRRRR ...., well, you know.

[FredZarguna]

It’s an easy mistake to make. The key thing is that the protons don’t care about where they are. They’re just not that smart. Classically, all they need is enough kinetic energy to get close enough to overcome the Coulomb barrier. Quantum mechanically, they don’t need quite that much energy, just enough for their proximity to be close enough that their wave functions have significant overlap (or equivalently, that their KE can “tunnel” through the Coulomb Barrier.)