The nonlinear interaction of waves can change the structural and radiative properties of plasmas. We describe the main features of a fully ionized unmagnetized plasma affected by strong Langmuir turbulence characterized by nonlinear wave collapse, and propose a simple model for evaluating the changes expected on a hydrogen line shape affected by such conditions. Our model is based on a stochastic renewal model using an exponential waiting time distribution and a half-normal probability density function for the electric field magnitude of the turbulent wave packet. The first results obtained with a simulation calculation of the hydrogen L  line show that strong Langmuir turbulence can provide an additional broadening to a Stark profile.

Abstract:The shape of atomic spectral lines in plasmas contains information on the plasma parameters, and can be used as a diagnostic tool. Under specific conditions, the plasma located at the edge of tokamaks has parameters similar to those in magnetic white dwarf stellar atmospheres, which suggests that the same line shape models can be used. A problem common to tokamak and magnetic white dwarfs concerns the modeling of Stark broadening of hydrogen lines in the presence of an external magnetic field and the related Zeeman effect. In this work, we focus on a selection of issues relevant to Stark broadening in magnetized hydrogen plasmas. Various line shape models are presented and discussed through applications to ideal cases.

We examine the possibility for a diagnostic of energetic particle beams based on passive spectroscopy, with a focus on the atomic lines observed in the edge region of tokamaks. Our investigation employs a quasi‐linear model for the collective electric field generated by the plasma‐beam instability. If the beam is sufficiently energetic, the electric field can be comparable to the thermal Holtsmark microfield, and the corresponding Stark effect on atomic energy levels can be observable on spectra. We investigate this issue and perform new hydrogen line shape calculations. The applicability of the model to the diagnostics of runaway electrons is discussed.

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