Investigation of negative triangularity plasma in terms of the n=0 resistive wall mode

Recently, negative triangularity (NT) plasmas have shown advantages over positive triangularity (PT) counterparts, including reduced electron heat transport and strong core performance concomitant with an L-mode edge. Despite these benefits, NT plasmas suffer from reduced elongation due decreased vertical stability. We have developed an n=0 resistive wall mode instability code (AVSTAB - Axisymmetric Vertical STABility), which calculates the marginally controllable elongation given a tokamak feedback parameter, to optimize the elongation of NT plasmas. NT equilibria generated with ECOM show increased Shafranov shifts compared to PT references, with more elongated inner flux surfaces which grow vertical instabilities. Poloidal beta has an opposite effect in NT and PT in terms of its influence on the marginally controllable elongation, which is increased with high poloidal beta only in the negative case. Interestingly, the conversed triangularity of a wall and plasma demonstrates elevated marginally controllable elongations for both negative and positive configurations. The feedback parameter of AVSTAB is improved for poloidal modes to reproduce various experimental results, including KSTAR discharges copper passive plates to control vertical instabilities.