Drift effects and ion temperature measurements in the scrape-off layer of W7-X

2D ion velocity and temperature measurements provided by coherence imaging spectroscopy (CIS) yield insight into scrape-off layer (SOL) transport in the W7-X island divertor. Experiments investigating drift effects by comparing plasmas with matched core parameters but opposite magnetic field directions, and therefore opposite drift transport directions, find that the poloidal E×B drift alters SOL parallel flows. In low-density plasmas (n_e ≤ 2×10¹⁹ m^-3), the poloidal E×B drift is the dominant particle transport mechanism and induces a large poloidal density asymmetry within the island. This causes the flow stagnation point, which is normally about halfway between targets, to shift toward the X-point in the drift direction, leading to near-unidirectional parallel flow throughout the SOL. As density increases, the effects of the poloidal E×B drift decrease substantially, and a counter-streaming flow pattern develops. In magnetic configurations with shorter connection lengths the impact of drifts on parallel flows is weaker. The ion temperature distribution at the divertor is also measured using a new multi-delay CIS instrument optimized to have minimal sensitivity to Zeeman splitting while retaining sufficient sensitivity to T_i. Temperatures ranging 15–35 eV over the divertor are observed and are in agreement with high-resolution spectrometer measurements.