High power ECRH and ECCD in moderately collisional ASDEX Upgrade Hmodes and status of EC system upgrade

¹ Max-Planck-Institut für Plasmaphysik, Garching, Germany
² Institut für Grenzflächenverfahrenstechnik und Plasmatechnologie, Universität Stuttgart, Stuttgart, Germany
³ Karlsruhe Institute of Technology, Karlsruhe, Germany
⁴ Institute of Applied Physics, RAS, Nizhny Novgorod, Russia
⁵ GYCOM Ltd., Nizhny Novgorod and Moscow, Russia

^a Corresponding author: Joerg.Stober@ipp.mpg.de

Published online: 12 March 2015

Abstract

This contribution deals with H-modes with significant heat exchange between electrons and ions, but which can still show large differences between electron and ion-temperatures especially inside half minor radius. These conditions are referred to as moderately collisional. A systematic study shows that an increasing fraction of electron heating increases the transport in the ion channel mainly due to the dependence of the ITG dominated ion transport on the ratio T_e/T_i in agreement with modeling. The rotational shear in the plasmas under study was so small that it hardly influences ITG stability, such that variations of the rotation profile due to a change of the heating method were of minor importance. These findings connect to studies of advanced tokamak scenarios using ECCD as a tool to modify the q-profile. The electron heating connected to the ECCD tends to increase the transport in the ion channel quite in contrast to the goal to operate at reduced current but with increased confinement. The confinement only increases as the fraction of ion heating is increased by adding more NBI. An ITER case was modeled as well. Due to the larger value of ν_ei ・ τ_E the ratio T_e/T_i is only moderately reduced even with strong electron heating and the confinement reduction is small even for the hypothetic case of using only ECRH as additional heating. Finally the paper discusses the ongoing upgrade of the AUG ECRH-system.