I have three questions about ICF, in the explanations i have read on the internet about ICF they all explain that the top layer of the pellet or the ablator is heated till it explodes and produces a reaction force which compress the D+T fuel. They then say shock waves are formed due to the collapsing fuel which compress it even further and eventually ignite the fuel. My question is why and when are the shock waves formed? My second one is what why is the D+T fuel in the pellet in two distinct layers after compression, the not so dense small center and the denser outer layer? My last question is when are the alpha particles created and what is its role? Are they formed when the fusion is underway? then why are they needed to heat up the fuel? or are they formed before the fusion occurs? Thank you.