Magnetohydrodynamic Stability of Negative Triangularity Plasmas

The aim of this work is to investigate the stability of negative triangularity, magnetically confined plasmas. The work is carried out at Consorzio RFX and within the framework of EUROfusion Tokamak Exploitation Work Package. The chief reason behind this investigation is the recent rise in the interest surrounding negative triangularity plasmas, seeing that they seem to be more stable and lead to power losses lower than positive triangularity while requiring less net auxiliary power to reach an acceptable confinement. The stability properties of different plasmas are explored starting from the RFX-mod shaped tokamak results and exploring projections to negative triangularity. Recent discharges of the TCV experiment are then analyzed, comparing stability properties between negative and positive triangularity plasmas. This comparative analysis is carried out by means of two different codes, namely CHEASE and MARS-F; the first being an equilibrium code which solves the Grad-Shafranov equation in weak form, and the second one a linear resistive- MHD code which solves the linear stability of a plasma. Results obtained by numerical modeling of real plasma discharges showed that triangularity can indeed play a role in stabilizing the resistive modes both for low-q0 and high-q0 plasmas, while it does not significantly affect the structure and dynamics of ideal modes.