Stability and toroidal rotation properties of highly shaped plasmas in the TCV tokamak

Abstract

Abstract Magnetohydrodynamic (MHD) instabilities and plasma rotation have various im-pacts on particle and thermal transport in toroidal plasmas. MHD instabilitiesdegrade the confinement, limit the maximum achievable plasma pressure, andcan lead to plasma disruptions. Plasma rotation is observed to have beneficialeffects on global instabilities and improve confinement through the reduction ofturbulent transport. Plasma rotation and stability are strongly coupled, influenc-ing each other in a complicated fashion. The Tokamak `a Configuration Variable (TCV), unique in its plasma shaping capabilities, is equipped with a flexible auxil-iary heating system (ECRH) and several diagnostics allowing us to study the effectof the plasma shape on stability in a wide range of scenarios. TCV also provides formeasurements of carbon toroidal velocity in the absence of external momentuminput, an experimental condition poorly studied in the past but of major interestfor an accurate prediction of the toroidal rotation in future large experiments.The work presented in this thesis may be divided into two parts. In the firstpart, we focus on plasma instabilities appearing in three different TCV scenarios.These instabilities limit the achievable maximum pressure and current density.New features and previously unnoticed dependencies are shown. In the secondpart of this thesis, we experimentally study the plasma rotation properties andtheir relation with the plasma parameters and MHD activity. The new insighton spontaneous rotation may help in constructing a complete model of plasmarotation in tokamaks.During the initial plasma current rise, edge MHD instabilities are commonlyobserved in most tokamaks when the edge safety factor