The divertor and the pumping system of Wendelstein 7-X is designed for stationary operation at various modes of operation. Maximum fluxes up to 1024 electron–ion-pairs/s are expected at the targets. Various cases of plasma–wall interaction have to be considered: at low densities convective power losses and proceeding to higher densities a high recycling mode, including detachment dominated by radiation. External fluxes (NBI, gas puffing and pellet injection) up to 1022 particles/s have to be pumped. The geometry of the target plates, the installation of additional baffle plates and the position of the pumping gap were optimised on the basis of numerical studies with the 3D neutral particle code EIRENE. For particle exhaust turbomolecular pumps (TMPs) and cryo-panels will be installed. Taking in account the capabilities of the TMP in the magnetic stray field an effective pumping speed for H2 of 4200 l/s at one divertor box will be reached. Including the cryo-panels integrated inside the divertor boxes a total pumping speed of up to 200 000 l/s will be provided.

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 non-axisymetric 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.

For operation within a wide range of plasma and magnetic parameters an open divertor structure of the Wendelstein 7-X stellarator (optimised HELIAS configuration with superconducting coils, main parameters: R = 5.5 m, a = 0.55 m, B = 3 T, rotational transform variable between 5/6 and 5/4) has been developed. The most critical components of the divertor are ten 3D-shaped target surfaces, located along the “helical edge” of the five-fold rotational symmetry magnetic configuration of the machine. The plasma outflow concentrates on the target areas, designed to withstand a maximum stationary heat flux of 10 MW/m2. To prevent excessive radiation losses all plasma facing components will be manufactured using low-Z materials, e.g. CFC, B4C. The paper presents the optimised design of the target plates, which takes into account the latest results of the physics, the requirements of the heating and diagnostic systems, the manufacturing costs and the mounting operations in order to build a technical reliable system.

The open divertor structure of the Wendelstein 7-X stellarator allows an effective particle and energy exhaust for a wide range of plasma and magnetic parameters. Ten 3D-shaped surfaces are located along the helical edge of the five-fold rotational symmetry magnetic configuration of the machine. The plasma outflow concentrates onto the target plates, so that the plasma is decoupled from the wall. The target plates are designed to withstand a maximum stationary heat flux of 10 MW/m2. The present optimised design of the target plates, which takes into account the latest results of the physics, the requirements of the heatings and diagnostics systems, the manufacturing costs and the mounting operations in order to build a technical reliable system is presented.