Towards a new image processing system at Wendelstein 7-X: From spatial calibration to characterization of thermal events

Wendelstein 7-X (W7-X) is the most advanced fusion experiment in the stellarator line and is aimed at proving that the stellarator concept is suitable for a fusion reactor. One of the most important issues for fusion reactors is the monitoring of plasma facing components when exposed to very high heat loads, through the use of visible and infrared (IR) cameras. In this paper, a new image processing system for the analysis of the strike lines on the inboard limiters from the first W7-X experimental campaign is presented. This system builds a model of the IR cameras through the use of spatial calibration techniques, helping to characterize the strike lines by using the information given by real spatial coordinates of each pixel. The characterization of the strike lines is made in terms of position, size, and shape, after projecting the camera image in a 2D grid which tries to preserve the curvilinear surface distances between points. The description of the strike-line shape is made by means of the Fourier Descriptors

Experimental confirmation of efficient island divertor operation and successful neoclassical transport optimization in Wendelstein 7-X

We present recent highlights from the most recent operation phases of Wendelstein 7-X, the most advanced stellarator in the world. Stable detachment with good particle exhaust, low impurity content, and energy confinement times exceeding 100 ms, have been maintained for tens of seconds. Pellet fueling allows for plasma phases with reduced ion-temperature-gradient turbulence, and during such phases, the overall confinement is so good (energy confinement times often exceeding 200 ms) that the attained density and temperature profiles would not have been possible in less optimized devices, since they would have had neoclassical transport losses exceeding the heating applied in W7-X. This provides proof that the reduction of neoclassical transport through magnetic field optimization is successful. W7-X plasmas generally show good impurity screening and high plasma purity, but there is evidence of longer impurity confinement times during turbulence-suppressed phases.EC/H2020/633053/EU/Implementation of activities described in the Roadmap to Fusion during Horizon 2020 through a Joint programme of the members of the EUROfusion consortium/ EUROfusio

Evidence of the Eldgjá (Iceland) eruption in the GISP2 Greenland ice core: relationship to eruption processes and climatic conditions in the tenth century

Glaciochemical studies and the evaluation of tephra in the GISP2 ice core provide information on the characteristics and potential environmental and climatic effects of the mid- to late AD 930s voluminous fissure eruption of Eldgjá, Iceland. The similarity in the chemical composition of basaltic glass shards found in a section of core dated at AD 938 ± 4 compared to proximal glass from the Eldgjá eruption verifies the presence of Eldgjá debris. A dacitic glass present in the same layer probably originated from Eldgjá as well, in which case Eldgjá was the primary contributor of sulphur-rich aerosols to the atmosphere in the late AD 930s. We cannot completely exclude the possibility that another explosive eruption in the AD 930s produced this dacitic glass. Estimated maximum stratospheric loading is 100 X 1012 g H 2SO4 over a 3-6 year period following the eruption, but loading could be as low as half of that value. A search of historical and proxy records for the late AD 930s to early 940s fail to show a consistent period of climatic cooling, especially considering the lack of an absolute date for the Eldgjá eruption. This inconsistent response is similar to that observed after the equally voluminous AD 1783 fissure eruption of Laki, Iceland, using the same proxy data sets. However, a marked drop in surface temperatures in the Northern Hemisphere follows the Laki eruption