A computer simulation technique is applied to the modelling of Balmer line shapes in dense divertor conditions. The spectral profile of lines with a high principal quantum number n is sensitive to Stark broadening and can be used as a density diagnostic. In contrast, an analysis of the shape of low or moderate n lines such as Dα (n = 3), Dβ (n = 4), and Dγ (n = 5) is more intricate because the Stark effect is weaker and can compete with thermal Doppler broadening. We examine this issue and address the relative contribution of the Stark and Doppler effects on the first Balmer lines. Analyses of experimental spectra are performed.
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.
In plasmas coupled to an external energy source like a beam of energetic electrons, one can observe the non‐linear coupling of Langmuir waves with ion sound and electromagnetic waves. This non‐linear interaction of waves changes the structural and radiative properties of plasmas. Coherent wave packets are trapped in regions of high intensity, and are subjected to a wave collapse cycle. We show that the electric field of the wave packets can modify the spectral lines emitted by hydrogen atoms. Our model for this field is a sequence of envelope solitons oscillating at the plasma frequency or the upper hybrid frequency. The calculations presented concern the Hα and Hβ Balmer lines of hydrogen and show the possible modifications of the line shapes if wave collapse conditions affect the edge plasma.
We present an analysis of hydrogen Balmer line shapes observed in two white dwarf spectra. One spectrum presents singlet lines while the second one presents lines with a triplet structure. The latter is a feature of the presence of a strong magnetic field. Using both Stark and Zeeman effects, we infer the density and the magnetic field. Our line shape calculations employ a computer simulation technique. The radiative transfer is accounted for through a onedimensional slab model.
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