Abstract In Wendelstein 7-X (W7-X), stable plasma detachment in ECRH hydrogen plasmas is routinely achieved with the standard magnetic configuration, containing five magnetic islands in the scrape-off layer (SOL). Plasma detachment induced by intrinsic carbon impurities is characterized by a high radiation fraction ( f rad ) with significantly reduced divertor heat load and particle flux. In this work, we present the radiation dynamics during the detached plasma (DP) phase, such as the shift of radiation zones in …

For over 10 years, several bolometer sensors with different properties have been tested in the IBOVAC facility. The aim has been to develop a bolometer sensor that can be operated in ITER and can withstand harsh operating conditions. For this purpose, important physical properties of the sensors, i.e., cooling time constant τ, normalized heat capacity κ, and normalized sensitivity sn, have been characterized in a vacuum condition and at various temperatures up to 300 °C. The calibration is achieved by ohmic heatin…

The ITER bolometer diagnostic shall provide the measurement of the total radiation emitted from the plasma, a part of the overall energy balance. Up to 550 lines-of-sight will be installed in ITER in 71 cameras of various sizes and types. The sensor holder, the component inside those cameras to provide attachment and signal connections to the sensor itself, might vary in shape within each camera. However, concepts for implementing electrical connections and handling of loads are very similar, if not identical. Tak…

The algorithm for bolometer tomography at Wendelstein 7-X (W7-X) has been recently improved using a novel regularization functional, based on relative gradient smoothing (RGS) of the sought radiation profile. It has been validated using radiation patterns provided by 3D modeling under real plasma conditions as phantoms and then applied to bolometer measurements performed during the first divertor operation phase of W7-X. The following results are presented: 1) edge-localized 2D radiation patterns with clearly reso…

Abstract The W7-X stellarator has so far performed experiments under both limiter and divertor conditions. The plasma is mostly generated by ECR-heating with powers up to 6.5 MW, and the plasma density is usually limited by the radiation losses from low-Z impurities (such as carbon and oxygen) released mainly from the graphite targets. The present work first summarizes the radiation loss fractions f rad achieved in quasi-stationary hydrogen plasmas in both operational phases, and then shows how impurity radiation …