Erosion and redeposition pattern on the W7-X graphite test divertor unit tile

A set of plasma-facing components was retrieved fom the W7-X vessel afcer OPl.2b campaign with an inertially cooled Test Divertor Unit (TDU) and analyzed postmortem to provide data on the plasma-surface interactions processes in the complex device geometry. In ehe present study, the lower TDU horizontal target (HT) graphite tile HMl 9TM400hTE2 exposed to the plasma du ring both OP 1.2 campaigns was examined. The surface modification of the material caused by the plasma-wall interactions was determined. The study employed several microscopy mcthods including SEM, FIB, STEM, TEM, EDX, and optical profilomecry which showed that (i) distinct erosion zone was located at the inner HT strike line position, (ii) the area covered by a pronounced deposit was located adjacent the erosion zone, (iii) the target finger substructures positioned close to the outboard side was unaltered, and (iv) significant changes to surface roughness values along the length of the plate occurred

Deposition of 13C tracer and impurity elements on the divertor of Wendelstein 7-X

Carbon impurity transport and deposition were investigated in the Wendelstein 7-X stellarator by injecting isotopically labelled methane ((CH4)-C-13) into the edge plasma during the last plasma operations of its Operational Phase (OP) 1.2B experimental campaign. C-13 deposition was measured by secondary ion mass spectrometry (SIMS) on three upper divertor tiles located on the opposite side of the vessel to the(13)CH(4) inlet. The highest C-13 inventories were found as stripe-like patterns on both sides of the different strike lines. These high deposition areas were also analysed for their impurity contents and the depth profiles of the main elements in the layers. Layered deposition of different impurity elements such as Cr, Ni, Mo and B was found to reflect various events such as high metallic impurities during the OP1.2A and three boronizations carried out during OP1.2B.Peer reviewe

Real-time detection of overloads on the plasma-facing components of Wendelstein 7-X

Wendelstein 7-X (W7-X) is the leading experiment on the path of demonstrating that stellarators are a feasible concept for a future power plant. One of its major goals is to prove quasi-steady-state operation in a reactor-relevant parameter regime. The surveillance and protection of the water-cooled plasma-facing components (PFCs) against overheating is fundamental to guarantee a safe steady-state high-heat-flux operation. The system has to detect thermal events in real-time and timely interrupt operation if it detects a critical event. The fast reaction times required to prevent damage to the device make it imperative to automate fully the image analysis algorithms. During the past operational phases, W7-X was equipped with inertially cooled test divertor units and the system still required manual supervision. With the experience gained, we have designed a new real-time PFC protection system based on image processing techniques. It uses a precise registration of the entire field of view against the CAD model to determine the temperature limits and thermal properties of the different PFCs. Instead of reacting when the temperature limits are breached in certain regions of interest, the system predicts when an overload will occur based on a heat flux estimation, triggering the interlock system in advance to compensate for the system delay. To conclude, we present our research roadmap towards a feedback control system of thermal loads to prevent unnecessary plasma interruptions in long high-performance plasmas.This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014–2018 and 2019–2020 under grant agreement No 633053.Peer ReviewedArticle signat per 22 autors/es: Aleix Puig Sitjes* 1, Marcin Jakubowski 1, Dirk Naujoks 1, Yu Gao 1, Peter Drewelow 1, Holger Niemann 1, Joris Fellinger 1, Victor Moncada 2, Fabio Pisano 3, Chakib Belafdil 2, Raphael Mitteau 2, Marie-Hélène Aumeunier 2, Barbara Cannas 3, Josep Ramon Casas 4, Philippe Salembier 4, Rocco Clemente 4, Simon Fischer 1, Axel Winter 1, Heike Laqua 1, Torsten Bluhm 1, Karsten Brandt 1, and The W7-X Team † 1. Max-Planck-Institut für Plasmaphysik, Wendelsteinstr. 1, 17491 Greifswald, Germany / 2. Commissariat à l’Énergie Atomique et aux Énergies Alternatives (CEA), Institut de Recherche sur la Fusion par Confinement Magnétique (IRFM), F-13108 Saint Paul-lez-Durance, France / 3. Department of Electrical and Electronic Engineering, University of Cagliari (UniCa), Piazza d’Armi, 09126 Cagliari, Italy / 4. Department of Signal Theory and Communications, Universitat Politècnica de Catalunya (UPC), Jordi Girona 1-3, 08034 Barcelona, Spain / * Author to whom correspondence should be addressed. / † Membership of the Team Name is provided in Acknowledgments.Postprint (published version

Analysis of the neutral fluxes in the divertor region of Wendelstein 7-X under attached and detached conditions using EMC3-EIRENE

This paper analyzes the neutral fluxes in the divertor region of the W7-X standard configuration for different input powers, both under attached and detached conditions. The performed analysis is conducted through EMC3-EIRENE simulations. They show the importance of the horizontal divertor to generate neutrals, and resolve the neutral plugging in the divertor region. Simulations of detached cases show a decrease in the number of generated neutrals compared to the attached simulations, in addition to a higher fraction of the ion flux arriving on the baffles during detachment. As the ionization takes place further inside the plasma during detachment, a larger percentage of the generated neutral particles leave the divertor as neutrals. The leakage in the poloidal and toroidal direction increases, just as the fraction of collected particles at the pumping gap. The fraction of pumped particles increases with a factor two, but stays below one percent. This demonstrates that detachment with the current target geometry, although it improves the power exhaust, is not yet leading to an increased particle exhaust

Real-Time Detection of Overloads on the Plasma-Facing Components of Wendelstein 7-X

Wendelstein 7-X (W7-X) is the leading experiment on the path of demonstrating that stellarators are a feasible concept for a future power plant. One of its major goals is to prove quasi-steady-state operation in a reactor-relevant parameter regime. The surveillance and protection of the water-cooled plasma-facing components (PFCs) against overheating is fundamental to guarantee a safe steady-state high-heat-flux operation. The system has to detect thermal events in real-time and timely interrupt operation if it detects a critical event. The fast reaction times required to prevent damage to the device make it imperative to automate fully the image analysis algorithms. During the past operational phases, W7-X was equipped with inertially cooled test divertor units and the system still required manual supervision. With the experience gained, we have designed a new real-time PFC protection system based on image processing techniques. It uses a precise registration of the entire field of view against the CAD model to determine the temperature limits and thermal properties of the different PFCs. Instead of reacting when the temperature limits are breached in certain regions of interest, the system predicts when an overload will occur based on a heat flux estimation, triggering the interlock system in advance to compensate for the system delay. To conclude, we present our research roadmap towards a feedback control system of thermal loads to prevent unnecessary plasma interruptions in long high-performance plasmas

Heat and particle exhaust in high-performance plasmas in Wendelstein 7-X

The paper reports for the first time the heat and particle exhaust at the plasma boundary through various edge diagnostics for the high-performance plasma obtained after pellet injection on Wendelstein 7-X. The plasma density at the edge is found to be reduced by a factor of 2 in the high-performance phase, supporting the previously reported density peaking at the plasma centre. The plasma beta effect on the magnetic topology is reflected by the appearance of the second strike line, which is well understood with simulation. However, during the rapid decay phase of the enhanced confinement, a transient localized heat flow of up to 16 MW m-2 is observed at the leading edge of a poorly cooled divertor component, which has not been understood but raises concerns about machine safety

Heat and particle exhaust in high-performance plasmas in Wendelstein 7-X

The paper reports for the first time the heat and particle exhaust at the plasma boundary through various edge diagnostics for the high-performance plasma obtained after pellet injection on Wendelstein 7-X. The plasma density at the edge is found to be reduced by a factor of 2 in the high-performance phase, supporting the previously reported density peaking at the plasma centre. The plasma beta effect on the magnetic topology is reflected by the appearance of the second strike line, which is well understood with simulation. However, during the rapid decay phase of the enhanced confinement, a transient localized heat flow of up to 16 MW m−2 is observed at the leading edge of a poorly cooled divertor component, which has not been understood but raises concerns about machine safety

Tutorials at PPSN 2016

PPSN 2016 hosts a total number of 16 tutorials covering a broad range of current research in evolutionary computation. The tutorials range from introductory to advanced and specialized but can all be attended without prior requirements. All PPSN attendees are cordially invited to take this opportunity to learn about ongoing research activities in our field