Solid-Density Ion Temperature from Redshifted and Double-Peaked Stark Line Shapes.

Area of Science:

• Plasma Physics
• Atomic Physics
• Spectroscopy

Background:

• Helium-beta (Heβ) spectral line shapes are crucial for diagnosing temperature and density in dense plasmas.
• Previous models using dipole approximation struggled to resolve ambiguities between electron density and ion temperature.

Purpose of the Study:

• To present Heβ line shapes measured from solid-density plasmas with minimized gradients.
• To develop and apply a new line shape model that resolves the electron density-ion temperature ambiguity.
• To investigate ion-electron thermal equilibrium in dense plasmas.

Main Methods:

• High-spectral-resolution measurements of Heβ line shapes from solid-density plasmas.
• Comparison of experimental line shapes to theoretical models, including a Markov chain Monte Carlo framework.
• Application of a line shape model incorporating full Coulomb interaction for electron broadening.

Main Results:

• Measured Heβ line shapes exhibit Stark broadening, redshifts, and double-peaked structures.
• The new model, using full Coulomb interaction, successfully resolves the ambiguity between electron density (ne) and ion temperature (Ti).
• Plasma densities were determined to be 80-100% of solid density.
• Strong evidence suggests that ions and electrons are not in thermal equilibrium in these dense plasmas.

Conclusions:

• The developed line shape model provides a more accurate method for diagnosing dense plasmas.
• The study provides the first strong evidence of non-thermal equilibrium between ions and electrons in dense plasmas.
• This experimental platform and diagnostic technique offer a promising new approach for studying ion-electron equilibration.