> What stops you from using the "even tinier piece pellet of hydrogen"[sic] from initiating fusion in a slightly less tiny pellet of hydrogen that it's sitting on top of, which initiates fusion in a slightly less tiny pellet of hydrogen, and so on? Aside from concern for your own survival, of course.
The same thing that stops you from igniting the initial pellet with the hohlraum - you don't have anything creating the kind of confinement necessary to keep the plasma together.
The only thing allowing the plasma to get hot enough for fusion is the initial velocity of the inward-spreading shockwave from the initial explosion of the outer shell of the pellet. As the velocity of this shockwave inevitably decreases, confinement is inevitably lost and the plasma dissipates and cools down.
Probably in principle you could use the energy of the first pellet's plasma to cause similar shockwaves in a second, larger pellet and so on, but that requires an entirely different geometry, its not just a matter of putting the second pellet close to the first one.
The same thing that stops you from igniting the initial pellet with the hohlraum - you don't have anything creating the kind of confinement necessary to keep the plasma together.
The only thing allowing the plasma to get hot enough for fusion is the initial velocity of the inward-spreading shockwave from the initial explosion of the outer shell of the pellet. As the velocity of this shockwave inevitably decreases, confinement is inevitably lost and the plasma dissipates and cools down.
Probably in principle you could use the energy of the first pellet's plasma to cause similar shockwaves in a second, larger pellet and so on, but that requires an entirely different geometry, its not just a matter of putting the second pellet close to the first one.