Advanced electron cyclotron heating and current drive experiments on the stellarator Wendelstein 7-X

¹ Max-Planck-Institute for Plasma Physics, Greifswald, Germany
² Laboratorio Nacional de Fusión, CIEMAT, Madrid, Spain
³ Institute for Interfacial Process Engineering and Plasma Technology, University Stuttgart, Germany
⁴ Institute of Pulsed Power and Microwave Technology, Karlsruhe Institute of Technology (KIT), Germany
⁵ Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543, USA
⁶ National Institute for Fusion Science, Toki 509-5292, Japan
⁷ Laboratory for Plasma Physics, ERM/KMS, Brussels, Belgium

^* Corresponding author: torsten.stange@ipp.mpg.de

Published online: 23 October 2017

Abstract

During the first operational phase (OP 1.1) of Wendelstein 7-X (W7-X) electron cyclotron resonance heating (ECRH) was the exclusive heating method and provided plasma start-up, wall conditioning, heating and current drive. Six gyrotrons were commissioned for OP1.1 and used in parallel for plasma operation with a power of up to 4.3 MW. During standard X2-heating the spatially localized power deposition with high power density allowed controlling the radial profiles of the electron temperature and the rotational transform. Even though W7-X was not fully equipped with first wall tiles and operated with a graphite limiter instead of a divertor, electron densities of n _e > 3·10¹⁹ m^-3 could be achieved at electron temperatures of several keV and ion temperatures above 2 keV. These plasma parameters allowed the first demonstration of a multipath O2-heating scenario, which is envisaged for safe operation near the X-cutoff-density of 1.2·10²⁰ m^-3 after full commissioning of the ECRH system in the next operation phase OP1.2.