The role of MHD in the sustainment of electron internal transport barriers and H-mode in TCV

Abstract

Advanced scenarios exhibit improved confinement properties, which make them attractive candidate for ITER. For these to be achieved, the sustainment of transport barriers and therefore high pressure gradients is inherent. Their stability properties both in the transient and steady state phases is a major issue [1], because of the relationship between high performances and proximity to a stability limit. Core MHD modes are one of the key issues in the development and sustainment of transport barriers, as they degrade the confinement properties and, in the worse case, disrupt the plasma. The understanding of the underlying physics can provide the means of finding regimes without modes. In TCV (Tokamak à Configuration Variable) H-mode and electron internal transport barriers (eITBs) have been obtained with different schemes, usually accompanied by various types of MHD phenomenon [2, 3, 4]. In this paper we focus on the low-shear Quasi-Stationary ELM free H-mode (QSEFHM) scenarios [4], which displays infrequent sawteeth and/or NTMs. In addition to that, high-performance eITBs shots are discussed, during which a variety of resistive to ideal modes are observed and ascribable to the infernal stability limit [3, 5]. Analysis of data from TCV highest performance discharges can clarify the potential threats of MHD modes in advanced scenarios. MHD core analysis of the QSEFHM [4], and of eITBs is presented, focusing on the existence of stability windows.