Highly charged ions in a weakly coupled plasma: an exact solution
  The ion sphere model introduced long ago by Salpeter is placed in a rigorous theoretical setting. The leading corrections to this model for very highly charged but dilute ions in thermal equilibrium with a weakly coupled, one-component background plasma are explicitly computed, and the subleading corrections are shown to be negligibly small. Such analytic results for very strong coupling are rarely available, and they can serve as benchmarks for testing computer models in this limit. 
Lowell S. Brown, David C. Dooling and Dean L. Preston