LOCAL IMPURITY PUFFING AS A SCRAPE-OFF LAYER DIAGNOSTIC ON THE ALCATOR C-MOD TOKAMAK

A capillary injection system has been installed on Alcator C-Mod which allows the localized introduction of gaseous species at a variety of poloidal locations. An experimental program has been undertaken to obs erve impurity puffs with a CCD camera through appropriate optical filt ers. The comet-like shape of an ion line emission plume formed in the region of an injection graphically displays the direction of backgroun d deuterium flow as well as that of the poloidal impurity ion drift. P arallel and cross-field one-dimensional fluid models are used to chara cterize the plume shapes and to deduce the background plasma temperatu re, the parallel now velocity and the poloidal drift velocity of the i mpurity ion. Model results are benchmarked against simulations of DIVI MP, a Monte Carlo code, and fast scanning probe measurements. The expe riments present a novel diagnostic technique to elucidate local edge i mpurity transport.