  We derive a quantum master equation for an atom coupled to a heat bath
represented by a charged particle many-body environment. In Born-Markov
approximation, the influence of the plasma environment on the reduced system is
described by the dynamical structure factor. Expressions for the profiles of
spectral lines are obtained. Wave packets are introduced as robust states
allowing for a quasi-classical description of Rydberg electrons. Transition
rates for highly excited Rydberg levels are investigated. A circular-orbit wave
packet approach has been applied, in order to describe the localization of
electrons within Rydberg states. The calculated transition rates are in a good
agreement with experimental data.
