Characterizing parallel flows in high performance pellet discharges at W7-X

The radial electric field and plasma flows of high-performance pellet discharges at W7-X are investigated using measurements from the x-ray imaging crystal spectrometer (XICS). In high-performance pellet discharges at W7-X, substantial evolution of flows has been observed, with indications that parallel flows might exceed neoclassical predictions. To explore this further, the evolution of plasma flows – with a focus on the parallel component – will be analyzed using charge exchange recombination spectroscopy (CXRS) as well as an updated XICS analysis that includes consideration of parallel Pfirsch-Schlüter flows during the tomographic inversion. We will compare the measurements of plasma flows with those predicted by neoclassical theory using SFINCS simulations. Of interest is also how these flows are connected to the changes in turbulent transport regimes that have been observed after pellet injection. Further understanding of the flow evolution and its effects will improve understanding of the high-performance discharges and how they are achieved with pellet injection.