Effect of electron collisions on ion‐acoustic waves and heat flow

The damping rate of ion‐acoustic waves in a plasma is calculated by numerically solving the electron Fokker–Planck and cold‐ion fluid equations for arbitrary electron collisionality kλei and charge number Z. The damping rate reaches a maximum at kλei∼(Zme/mi)1/2, as predicted by fluid theory, but then remains above fluid‐theory predictions for kλei≳(Zme/mi)1/2. This enhancement is most significant for high‐Z plasmas, where the thermalization due to electron–electron (e–e) collisions is least effective. For kλei≫1, the damping approaches the collisionless Landau limit. The isotropic‐Rosenbluth‐potential approximation for e–e collisions gives rise to errors of up to 10% in the damping rates. A further approximation that involves adjusting the e–i angular scattering collision strength to simulate the contribution from e–e collisions is found to be similarly accurate. In the high‐Z limit, there is a strong reduction in the effective thermal conductivity κ relative to the classical Spitzer–Harm value κSH for k...