Line shapes in the presence of nonlinear wave collapse in a plasma

In a plasma submitted to an external source of energy, such as a beam of energetic charged particles, Langmuir, ion sound and electromagnetic wave may couple nonlinearly and change the structural and radiative properties of the plasma. Wave packets localize in many regions of the plasma and evolve cyclically toward very large values of the electric field. How the dipole autocorrelation functions (Fourier transform of the line shape) are modified by such conditions may be investigated with the help of a renewal model for the electric field. We compare the results of our model to the thermal line shape of Lyman α in low density plasmas.