Speaker
Description
We extend the MHD spectroscopy framework proposed earlier [1] to incorporate new effects arising from the modification of the geodesic acoustic mode (GAM) frequency by the anisotropic energetic particles (EP) pressure in the presence of the magnetic field reversed shear. These enhancements offer dual advantages: improving the accuracy of $q_{min}$ reconstruction and enabling the inference of EP pressure under specific assumptions about their distribution function. We refer to this approach as GAM MHD spectroscopy, as it leverages the GAM frequency, which is sensitive to the parametrization of the EP distribution function.
Traditional MHD spectroscopy typically relies on measurements of Alfvén Eigenmode (AE) frequencies and mode numbers to refine equilibrium reconstructions, including tracking the time evolution of the safety factor.
Building on this, we propose the application of recently refined gyrokinetic theory of energetic particle-driven GAM (EGAM) instabilities [2]. By comparing the measured minimum frequency of reverse-shear Alfvén eigenmodes (RSAEs) with theoretically predicted values, this approach facilitates the inference of EP pressure profiles, particularly in spherical tokamak (ST) devices where EP pressure constitutes a fraction of the total plasma pressure.
The proposed GAM MHD spectroscopy is applied to analyze ST40 discharges, demonstrating its potential for improving equilibrium reconstruction and EP pressure diagnostics.
References
[1] A. Fasoli, D. Testa, H. L. Berk, et al., Plasma Phys. Control. Fusion 44, B159 (2002).
[2] F. Camilo de Souza, N. N. Gorelenkov, A. Elfimov, et al., J. Plasma Phys 88, 905880308 (2022).
| Presentation type | Poster |
|---|
