Validating the ASCOT modelling of NBI fast ions in Wendelstein 7-X stellarator

The first fast ion experiments in Wendelstein 7-X were performed in 2018. They are one of the first steps in demonstrating the optimised fast ion confinement of the stellarator. The fast ions were produced with a neutral beam injection (NBI) system and detected with infrared cameras (IR), a fast ion loss detector (FILD), fast ion charge exchange spectroscopy (FIDA), and post-mortem analysis of plasma facing components. The fast ion distribution function in the plasma and at the wall is being modelled with the ASCOT suite of codes. They calculate the ionisation of the injected neutrals and the consecutive slowing down process of the fast ions. The primary output of the code is the multidimensional fast ion distribution function within the plasma and the distribution of particle hit locations and velocities on the wall. Synthetic measurements based on ASCOT output are compared to experimental results to assess the validity of the modelling. This contribution presents an overview of the various fast ion measurements in 2018 and the current modelling status. The validation and data-analysis is on-going, but the wall load IR modelling already yield results that match with the experiments

First divertor physics studies in Wendelstein 7-X

The Wendelstein 7-X (W7-X) optimized stellarator fusion experiment, which went into operation in 2015, has been operating since 2017 with an un-cooled modular graphite divertor. This allowed first divertor physics studies to be performed at pulse energies up to 80 MJ, as opposed to 4 MJ in the first operation phase, where five inboard limiters were installed instead of a divertor. This, and a number of other upgrades to the device capabilities, allowed extension into regimes of higher plasma density, heating power, and performance overall, e.g. setting a new stellarator world record triple product. The paper focuses on the first physics studies of how the island divertor works. The plasma heat loads arrive to a very high degree on the divertor plates, with only minor heat loads seen on other components, in particular baffle structures built in to aid neutral compression. The strike line shapes and locations change significantly from one magnetic configuration to another, in very much the same way that codes had predicted they would. Strike-line widths are as large as 10 cm, and the wetted areas also large, up to about 1.5 m(2), which bodes well for future operation phases. Peak local heat loads onto the divertor were in general benign and project below the 10 MW m(-2) limit of the future water-cooled divertor when operated with 10 MW of heating power, with the exception of low-density attached operation in the high-iota configuration. The most notable result was the complete (in all 10 divertor units) heat-flux detachment obtained at high-density operation in hydrogen

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

Why do they gamble and what does it mean? Latent class analysis of gambling motives among young male gamblers.

Background: Motives to gamble are important in the functional analysis of problematic gambling. This study examines the possibility of classifying young male gamblers based on their motives to gamble and compares the identified groups to validate the obtained classification. Method: Based on a screening survey among 2,681 young men from Bavaria, n=170 frequent or problem gamblers (Mage = 22.3 years, SD = 2.5) were recruited to participate in a survey with a 2-year follow-up. Latent class analyses (LCA) were conducted based on baseline answers to 10 items measuring five domains of gambling motives: enhancement, coping, self-gratification, and social and financial motives. The identified classes were compared regarding baseline gambling attitudes and impulsiveness as well as gambling behavior and gambling disorder (GD) criteria at baseline and follow-up. Results: Analyses revealed a four-class solution based on reported motives: ‘primarily fun-motivated gamblers’ (n=100, 58.8%), who gambled mostly for fun; ‘asset and self-gratification seekers’ (n=19, 11.2%) with a high risk of GD at baseline; ‘thrill seekers’ (n=42, 24.7%) with high impulsiveness; and ‘polymotivated coping gamblers’ (n=9, 5.3%) with a higher risk of GD than the ‘primarily fun-motivated gamblers’ in cross-sectional and longitudinal analyses. Conclusions: The identified group differences support the validity of the classification. ‘Thrill seekers’ and ‘polymotivated coping gamblers’ correspond to the impulsive and emotionally vulnerable pathways described by Blaszczynski and Nower (2002) respectively. The two other groups appear to be subtypes of the behaviorally conditioned type. Motivation-based classification offers a promising approach to identifying individuals with an elevated risk of GD