ABSENCE OF DICKE NARROWING IN X-RAY LASER PLASMAS

Present x-ray laser plasmas are in the intermediate coupling regime (0 .1 < Gamma < 4, Gamma = Z(2)e(2)/kTa, with a the ion sphere radius), w here the binary collision based arguments of low density plasma kineti c theory can be misleading. The difficulty of modeling the spectral ou tput from neonlike lasers at wavelengths near 200 Angstrom A has led t o the suggestion, based on a low density, electron screened, plasma mo del, that collisional (''Dicke'') narrowing may be important. Molecula r dynamics results, which include ion collisions and screening effects , are presented here. They indicate that the free-particle Doppler app roximation is still quite accurate for lambda approximate to 200 Angst rom A and Gamma less than or similar to 1. Collisional narrowing will become important at somewhat stronger couplings (T approximate to 5) a nd at this wavelength the diffusion approximation is reasonable for T > 10. Collisional narrowing is found to be small even for the higher d ensity (Gamma approximate to 4) nickel-like lasers operating near 45 A ngstrom A.