Modelling effects of edge density fluctuations on electron-cyclotron current drive used for neoclassical tearing mode stabilization

• Published in: Journal of plasma physics Vol. 87; no. 1
• Main Authors: Tsironis, C., Papagiannis, P., Bairaktaris, F., Valvis, S. I., Hizanidis, K.
• Format: Journal Article
• Language: English
• Published: Cambridge, UK Cambridge University Press 01.02.2021
• Subjects: Asymmetry; Asymptotic methods; Cyclotrons; Electron density; Experiments; Fluctuations; Invited Contributions from the 18th European Fusion Theory Conference; Magnetic fields; Plasma; Plasma physics; Plasmas (physics); Propagation; Ray tracing; Stabilization; Tearing; Transfer matrices; Wave propagation; plasma heating; fusion plasma; plasma waves
• ISSN: 0022-3778; 1469-7807
• DOI: 10.1017/S002237782000149X

In this work we study the undesired effects of electron density fluctuations (in the form of blob structures which may exist in the edge region of tokamak plasmas) to the electron-cyclotron wave propagation and current drive in connection to the efficiency of neoclassical tearing mode stabilization. Our model involves the evaluation of the driven current in the presence of density perturbations, by using a combination of a wave solver based on the transfer matrix and electromagnetic homogenization methods for the propagation part prior to and inside the region of these structures (where standard asymptotic propagation methods may not be valid due to the short-wavelength limit breakdown), with a ray tracing code including island geometry effects and current drive computation for the propagation past the perturbed region. The computed driven current is input into the modified Rutherford equation in order to estimate the consequences of the wave deformation (driven by the density fluctuations) to the mode stabilization.