The next step in the Wendelstein stellarator line is the large superconducting device Wendelstein 7-X, currently under construction in Greifswald, Germany. Steady-state operation is an intrinsic feature of stellarators, and one key element of the Wendelstein 7-X mission is to demonstrate steady-state operation under plasma conditions relevant for a fusion power plant. Steady-state operation of a fusion device, on the one hand, requires the implementation of special technologies, giving rise to technical challenges during the design, fabrication and assembly of such a device. On the other hand, also the physics development of steady-state operation at high plasma performance poses a challenge and careful preparation. The electron cyclotron resonance heating system, diagnostics, experiment control and data acquisition are prepared for plasma operation lasting 30 min. This requires many new technological approaches for plasma heating and diagnostics as well as new concepts for experiment control and data acquisition.

The magnetic diagnostics foreseen for the Wendelstein 7-X (W7-X) stellarator are diamagnetic loops to measure the plasma energy, Rogowski coils to measure the toroidal plasma current, saddle coils to measure the Pfirsch-Schlüter currents, segmented Rogowski coils (poloidal magnetic field probes) to add information on the distribution of the plasma current density, and Mirnov coils to observe magnetohydrodynamic modes. All these magnetic field sensors were designed as classical pick-up coils, after the time integration of induced signals for 1/2 hour had been successfully demonstrated.The long-pulse operation planned for W7-X causes nevertheless significant challenges to the design of these diagnostics, in particular for the components located inside the plasma vessel, which may be exposed to high levels of microwave (electron cyclotron resonance) stray radiation and thermal radiation. This article focuses on the tests and modelling performed during the development of the magnetic diagnostics and on the design solutions adopted to meet the conflicting requirements. * Corresponding author, email: endler@ipp.mpg.de 1 All pick-up coils foreseen for the initial operation phase of W7-X and their signal cable sections inside the plasma vessel and the cryostat are now installed, and their electronics and data acquisition are under preparation.

The stellarator experiment Wendelstein 7-X (W7-X) is designed for stationary plasma operation (30 minutes). Plasma facing components (PFCs) such as the divertor targets, baffles, heat shields and wall panels are being installed in the plasma vessel (PV) in order to protect it and other invessel components. The different PFCs will be exposed to different magnitude of heat loads in the range of 100 kW/m2 to 10 MW/m2 during plasma operation. An important issue concerning the design of these PFCs is the thermo-mechanical analysis to verify their suitability for the specified operation phases. A series of finite element (FE) simulations has been performed to achieve this goal. Previous studies focused on the test divertor unit (TDU) and high heat flux (HHF) target elements. The paper presents detailed FE thermo-mechanical analyses of a prototype HHF target module, baffles, heat shields and wall panels, as well as benchmarking against tests. Xuebing PengMr.Max Planck Institute for Plasma Physics, EURATOM Association,Greifswald, Germany 14 September 2012 Dear Dr. Ing.Olaf, Please accept the attached manuscript of the paper, named Thermo-mechanical analysis of Wendelstein 7-X plasma facing components, for SOFT-27 special issue. The paper is about the thermo-mechanical analysis of Wendelstein 7-X plasma facing components, including the high heat flux divertor targets, baffles, heat shields and wall panels, in order to verify their suitability for steady state operation.I greatly appreciate you taking time to read this letter and the paper, and am look forward to hearing from you. Best regardsSincerely yours, Xuebing Peng. Cover Letter Research Highlights Thermo-mechanical analysis of HHF divertor module TM-H09 shows that it can withstand heat loads of 10 MW/m 2 in steady state when the supports was optimized accordingly.  FE calculations indicate that the tiles of baffles and heat shields can withstand stationary heat loads of 250 kW/m 2 , but that the pulse length of plasma operation must be limited depending on the number of full load (500 kW/m 2 ) cycles.  Gap requirements for wall panels during assembly were defined based on several FE calculations. The stellarator experiment Wendelstein 7-X (W7-X) is designed for stationary plasma operation (30 minutes). Plasma facing components (PFCs) such as the divertor targets, baffles, heat shields and wall panels are being installed in the plasma vessel (PV) in order to protect it and other in-vessel components. The different PFCs will be exposed to different magnitude of heat loads in the range of 100 kW/m 2 to 10 MW/m 2 during plasma operation. An important issue concerning the design of these PFCs is the thermo-mechanical analysis to verify their suitability for the specified operation phases. A series of finite element (FE) simulations has been performed to achieve this goal. Previous studies focused on the test divertor unit (TDU) and high heat flux (HHF) target elements. The paper presents detailed FE thermo-mechanical analyses of a prototype HHF target modu...

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