The formation of shockwaves and the role of Alpha particles in ICF

[tripleA]

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.

 

[the_wolfman]

In general shock waves form as the result of large sudden changes. In ICF, this happens when they deliberately increase the intensity of the lasers.

Alpha particles are a product of the D-T fusion reaction. They carry about 20% of the energy produced in a fusion reaction. The other 80% is carried by a neutron (the other fusion product).

The ICF pellet is designed similar to a camp fire. When you light a camp fire you place small twigs and other kindling in the center and surround the kindling with bigger logs. You light the kindling with a match (or other means), and heat released from the kindling heats the bigger logs until they ignite. It is these bigger logs that provide most of the heat from the campfire.

In an ICF pellet, the low density region is the kindling. It requires a lot less energy to initiate fusion is this region. But once the low density region is lit, the heat from fusion rapidly heats the high density region (the big logs) to fusion temperatures. It is the burring of this high density region that (in theory) will produce most of the energy.

As an aside, NIF (the national ignition facility) has been under performing because turbulence is destroying the high density region before the low density region can ignite it. (This is like Smokey the bear running in and kicking you campfire apart just after you light the kindling). Reducing turbulence is key!