Speaker
Description
Recent advances in stellarator optimization have led to unprecedented improvement in neoclassical transport in Wendelstein 7-X [1] such that anomalous transport is contributing a significant portion of the transport, especially in the Scrape-Off-Layer (SOL) [2]. Here, we present isothermal fluid turbulence simulations using the BOUT++ framework [3,4] in the edge and scrape-off-layer (SOL) of an analytic stellarator configuration with an island divertor, thereby providing the first numerical insight into edge turbulence near islands in a stellarator. The overall transport follows a ballooning nature due to the dominant 1/R component of the curvature, but fluctuations are present throughout the island divertor region. It is determined that the island chain at the separatrix influences the amplitude and radial extent of the fluctuations. Fluxes not associated with ballooning transport can be observed near island X-points. The fluctuations exhibit a predominantly positive skewness, indicating blob-like perturbations for the transport into the outer SOL. It is determined that the separatrix is generally more correlated with the outer SOL, whereas the O-point regions
are decorrelated. The implications for W7-X, and the extension of a multi-fluid,global fluid turbulence framework to stellarator geometries will also be discussed.
This work has been carried out within the framework of the EUROfusion Consortium, funded by the European Union via the Euratom Research and Training Programme (Grant Agreement No 101052200 - EUROfusion). Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the European Commission. Neither the European Union nor the European Commission can be held responsible for them.
Prepared in part by LLNL under Contract DE-AC52-07NA27344. LLNL-JRNL-849204.
References:
[1] C. Beidler et al., Nature 596, 221 (2021)
[2] N. A. Pablant et al., Physics of Plasmas 25, 022508 (2018)
[3] B. D. Dudson et al., Phys. Computer Physics Communications 180, 1467 (2009)
[4] B. Shanahan, B Dudson and P Hill, hPlasma Physics and Controlled Fusion 61, 025007 (2019)
[5] B Dudson et al., arXiv:2303.12131 (2023)
