Extension of the TCV operating space towards higher elongation and higher normalized current

Recently, an experimental campaign has been launched on TCV with the aim of exploring and extending the limits of the operating space. The vertical position control system has been optimized, with the help of extensive model calculations, in order to allow operation at the lowest possible stability margin. In addition, the growth rate of the axisymmetric instability has been minimized by choosing optimum values for the plasma triangularity and squareness and by operating close to the current limit imposed by the n = 1 external kink mode. These measures have allowed us to reach record values of elongation, k = 2.8, and normalized current, I-N = 3.6, in a tokamak with standard aspect ratio, R/a = 3.5.