Modification of Transport in Burning Plasmas due to alpha-electron Collisions

Ignition in ICF requires alpha particles to transfer energy to the deuterium-tritium plasma via Coulomb collisions. For plasma temperatures < ~25 keV, the alphas transfer energy predominantly to the plasma electrons. The electron-electron collision time is much shorter than the alpha-electron collision time since the alpha number density is a small fraction of the electron number density. Therefore, it is usually assumed that the electron distribution function remains Maxwellian when alpha particles are present.

In this work it is shown that a net flux of alpha particles can perturb the electron distribution function from Maxwellian. The electron kinetic equation is solved in the presence of arbitrary populations of alpha particles to quantify this perturbation. The perturbation results in the transport of energy and momentum by the plasma electrons. In particular, it is shown that heat flow from hot to cooler regions of an igniting plasma can be increased by the flux of alpha particles that results from differences in reactivity between the regions. Burn propagation into cold fuel is also modified by this effect.