Investigation of MHD instabilities in tokamak plasmas Using biorthogonal decomposition of Mirnov coil data

Authors

• Habib Mehrniya ¹
• Mohammad Kazem Salem * ¹
• Ahmad Salar Elahi ¹

• Plasma Physics Research Center, Science and Research Branch, Islamic Azad University, P.O. Box: 14665‑678, Tehran, Iran

Abstract

Spatiotemporal signal analysis is essential in investigating magnetic fluctuations of tokamak plasmas. Signal analysis of Mirnov coils through biorthogonal decomposition (BD) can reveal the spatial structure and time evolution of magnetohydrodynamic (MHD) instabilities in a tokamak. This technique is comparable to singular value decomposition in terms of formulation. The present study calculates the probability of instability modes’ presence and identifies the dominant modes using the method above. Moreover, the relationship between the singular value entropy as a signal characteristic and magnetic field oscillations of Mirnov coils in the IR-T1 tokamak is investigated. This study evaluated the presence of active modes with and without applying a resonant helical field. The results indicate that when L=2 and L=3 are applied independently, the probability of m=2 & 3 active modes is greater than when the resonant helical field is absent. In contrast, by combining these two, the likelihood of the presence of these modes is reduced.

Keywords

• Biorthogonal decomposition
• Instability indicators
• Principal axes
• Singular values entropy