Calibrated helium and carbon ion flow measurements in the DIII-D divertor plasma

To explore the influence of drifts on ion flows in the DIII-D divertor and Scrape-Off-Layer (SOL), a calibrated Coherence Imaging System (CIS) views the lower divertor. A new tuneable calibration laser and precision wavemeter provide the rest wavelength for CIII 465 nm plasma emissions resulting in ≤ 1 km/s uncertainty in ion velocities that are in the range of 30 km/s in the divertor plasma. The 2-D line-integrated velocity images have been tomographically inverted to obtain maps of ion velocity. Both He⁺ and C²⁺ ion velocity maps were measured in both directions of the toroidal magnetic field B_T , and C²⁺ images were obtained in attached and detached L- and H-mode plasmas. The measured C²⁺ velocities are in the range of 20–30 km/s and are compared with UEDGE modeling with full drifts. While He II as a main ion is expected to be entrained in the plasma flow, the C²⁺ impurity flow involves the competition between the frictional and ion temperature gradient forces. Both the CIS data and UEDGE modeling agree that the C²⁺ flow is towards the divertor plates, but flips with the direction of B_T . In general, the experimental C²⁺ emission and flow profiles have a wider spatial extent than the UEDGE modeling.