Stark broadening under extreme plasma conditions

Broadening of spectral lines of atoms and ions primarily caused by electric fields from plasma electrons and ions can be important at electron densiti es ranging from Ne approximate to 0.1 cm(-3) (interstellar molecular clouds ) to N-e less than or similar to 10(25) cm(-3) (laser-fusion targets, atmos pheres of neutron stars), or N-e greater than or similar to 10(27) cm(-3) ( stellar interiors). At the low density extreme, lines useful for density de terminations are n-alpha radio-frequency lines of atoms and ions in Rydberg levels with principal quantum numbers up to about 600. At the other extrem e, astrophysicists are interested in helium- and hydrogen-like X-ray lines of iron, because of their importance in the energy transport from stellar c ores, or plasma physicists in analogous lines of argon, because their obser ved profiles give a measure of the compression achieved. Experiments on Sta rk broadening under well-defined and independently measured plasma conditio ns have been performed only for a relatively small portion of the huge rang e of densities and temperatures of interest. This leaves a heavy burden on theory and calculations for extrapolations into the more extreme regimes.