Control of the sawtooth instability by electron cyclotron heating and current drive in the TCV and ASDEX Upgrade tokamaks

Recently, there has been increased interest in avoiding the destabilization of neoclassical tearing modes (NTMs) by controlling the sawtooth instability which frequently provides a large enough seed island to trigger the growth of the NTM. Electron cyclotron heating (ECH) and current drive (ECCD) are prime candidates for such control as the all important deposition location can be adjusted using external control parameters alone. Sawtooth control studies have been carried out on the Tokamak à Configuration Variable (TCV) and ASDEX Upgrade tokamaks. The experiments and subsequent sawtooth period modeling help to determine the optimum locations for sawtooth period control and understand the mechanism by which this control is attained