Feedback stabilization of axisymmetric modes in the TCV tokamak using active coils inside and outside the vacuum vessel

A new vertical position control system, including an internal active coil, has become operational on TCV. The new system has made it possible to stabilize plasmas with open loop growth rates up to 4400 s(-1), currents up to 1.0 MA and elongations up to 2.58. The closed loop stability of the new system has been analysed with a numerical model in which the plasma is assumed to be undeformable, and the power supply outputs are delayed with respect to their inputs. Model predictions agree with the main experimental results.