On the polarization of shear Alfv\'en and acoustic continuous spectra in toroidal plasmas

TL;DR

This paper uses the FALCON code to analyze shear Alfvén and acoustic spectra in toroidal fusion plasmas, emphasizing mode polarization and the effects of plasma compression on continuous spectra.

Contribution

It introduces the application of the FALCON code with local Floquet analysis to study continuous spectra in realistic toroidal plasma equilibria.

Findings

Mode polarization is crucial for identifying physically relevant spectral branches.

Plasma compression significantly affects the structure of continuous spectra.

The slow sound approximation's validity is examined in the context of these spectra.

Abstract

In this work, the FALCON code is adopted for illustrating the features of shear Alfv\'en and continuous spectra in toroidal fusion plasmas. The FALCON codes employs the local Floquet analysis discussed in [Phys. of Plasmas \textbf{26} (8), 082502 (2019)] for computing global structures of continuous spectra in general toroidal geometry. As particular applications, reference equilibria for the Divertor Tokamak Test and ASDEX Upgrade plasmas are considered. In particular, we illustrate the importance of mode polarization for recognizing the physical relevance of the various branches of the continuous spectra in the ideal MHD limit. We also analyze the effect of plasma compression and the validity of the slow sound approximation.