The improved H-Mode at ASDEX Upgrade: A candidate for an ITER hybrid scenario

Full text: Since 1998 ASDEX Upgrade has developed a stationary regime of operation with improved core confinement for both electrons and ions in combination with a H-mode edge, called 'Improved H-Mode'. This scenario is characterized by a stationary q profile with central q close to 1, low magnetic shear in the centre, no sawteeth, a confinement factor with respect to H-mode of up to 1.4, and a normalized beta of around 3. The qualification of the improved H-mode as a 'hybrid scenario' for ITER is a central part of the ASDEX Upgrade programme. These studies focus on confinement and MHD stability in different parameter scans (q - edge, rho*, density), the role of sawteeth and NTMs, impurity transport, reactor relevant issues like strong electron heating and high edge densities with low amplitude ELMs, as well as the comparison experiments with other tokamaks like JET and DIII-D. ASDEX Upgrade with its flexibility in plasma shaping, high NBI power, ICRH, ECRH, and extended set of diagnostics plays a key role in the development and characterization of this scenario which potentially offers for ITER long pulses at reduced plasma current or higher Q values at the nominal plasma current. (author)