13C transport studies in L-mode divertor plasmas on DIII-D

¹³CH ₄ was injected with a toroidally-symmetric gas system into 22 identical lower-single-null L-mode discharges on DIII-D. The injection level was adjusted so that it did not significantly perturb the core or divertor plasmas, with a duration of ∼3 s on each shot, for a total of ∼300 T L of injected particles. The plasma shape remained very constant; the divertor strike points were controlled to ∼1 cm at the divertor plate. At the beginning of the subsequent machine vent, 29 carbon tiles were removed for nuclear reaction analysis of ¹³ C content to determine regions of carbon deposition. It was found that only the tiles inboard of the inner strike point had appreciable ¹³ C above background. Visible spectroscopy measurements of the carbon injection and comparisons with modeling are consistent with carbon transport by means of scrape-off layer flow.