The frequency of electron-ion collisions in a hot plasma
  It is shown that the anomalous resistivity, thermal conductivity, and magnetic pressure of hot plasmas can be explained by the assumption that the collisional electron-ion cross-section becomes constant above some critical temperature. This constant is determined by the size of ion (its electron envelope). It is shown also that this assumption follows from the consideration of interaction of a hot plasma with thermal radiation. 
Fedor V.Prigara