Impact of Poloidal Density Variation on Radial Impurity Transport

Results are presented from a first of its kind experiment to test the impact of poloidal asymmetries of impurity density on their flux-surfaced averaged radial transport in tokamak plasmas. Laser blow-off of molybdenum was introduced in ICRH heated, Alcator C-Mod L-mode plasmas where changes to the hydrogen minority resonance layer were used to modify the in/out asymmetry between -0.2 \textless~n$_{\mathrm{z,cos}}$/$\langle$n$_{\mathrm{z}}\rangle$ \textless~0.2 at mid-radius. Changes in the impurity confinement time by a factor of two, measured using radiated power and vacuum ultraviolet spectroscopy diagnostics, are correlated to changes in the asymmetry. Radial profiles of Mo$^{32+}$ for r/a \textless~0.8 are measured using x-ray imaging crystal spectroscopy, and are used to constrain STRAHL simulations which provide details on changes in the gradient scale length of the impurity density.