Divertor concept for the W7-X stellarator and mode of operation

Abstract

A favourable property of the stellarator concept is the potential of stationary operation within a magnetic configuration maintained by a superconducting coil system. For proof of principle the stellarator Wendelstein 7-X is presently under construction at Greifswald, Germany, and the start of operation is planned for 2007. The magnetic configuration of the confinement is a nonaxisymetric three-dimensional configuration with a helix-like magnetic axis and five identical magnetic field periods. As a first-step divertor design, an open divertor structure has been chosen, which benefits from the inherent divertor property of the magnetic configuration. The system will allow an effective particle and energy exhaust for a wide range of plasma and magnetic parameters. Experimental tools, e.g. localized heating, various heating schemas, gas feed and pellet injection, impurity doping and variation of the pumping speed together with appropriate diagnostics are provided. The purpose is to investigate different modes of operation for the divertor system and to evaluate an extended database for further improvement of the divertor.The main heating method will be 140 GHz ECR as a cw heat source of 10 MW. Additional heating schemes are ICRF and NBI.

On the W7-X divertor performance under detached conditions

“…The W7-X island divertor W7-X follows the island divertor concept tested on W7-AS. Ten identical divertor modules consisting of target and baffle plates are up/down-symmetrically installed around the beanshaped planes, preserving the five-fold periodicity and stellarator symmetry of the machine [14]. In order not to restrict the operational configuration flexibility of W7-X, the divertor plates are not optimized with respect to any specific configuration.…”

Initial Exploration of High-Field Pulsed Stellarator Approach to Ignition Experiments

“…changing the currents in coils. It would change the size and position of the magnetic islands [11,44], increasing the wet area and smoothing the heat load on the targets [49][50][51]. Doubling the wet area of an improved quasi-isodynamic configuration is assumed in Fig.…”

Island divertor configuration design for a quasi-axisymmetric stellarator CFQS

“…In LHD, the intrinsic helical divertor has divertor magnetic field lines connecting the ergodic boundary layer of the core region and the divertor plates on the wall (Masuzaki et al 2006;Kobayashi et al 2010). In W7-X, the island divertor provides a sophisticated divertor structure combined with low-order islands created near the boundary of the core confinement region (Renner et al 2002;Suzuki & Geiger 2016). Intensive theoretical and experimental researches of island divertor performances have been reported, including the former device of W7-AS, which preceded the W7-X programme (Feng et al 2006(Feng et al , 2011(Feng et al , 2016Xhang et al 2019).…”