Measurements of Heat-flux Footprints at the Inner Divertor Target of Alcator C-Mod

IR thermography has been used to measure the footprints of heat-flux onto the inner high-field side divertor target in C-Mod in a variety of discharge conditions. These include different magnetic-configurations (LSN, near-DN, and USN, with particular attention to near-DN configurations) and different confinement modes (I-mode, EDA H-mode, and ELM-free H-mode). Heat-fluxes and heat-flux widths during I-mode are especially of interest because of the enhanced power to the inner target that occurs in the ``reversed'' toroidal field condition that is favorable for I-mode. We find that under LSN conditions the footprints can be described by an ``Eich-fit'' function, with a characteristic length for heat-flux spreading into the SOL ($\lambda _{\mathrm{q}})$ and a characteristic width for heat-flux spreading along the divertor leg. We find that the minimum values of $\lambda _{\mathrm{q}}$ in I-mode are consistent with the multi-machine observations that the H-mode $\lambda_{\mathrm{q}}$ on the outer target scales inversely with B$_{\mathrm{pol}}$, with $\lambda_{\mathrm{q}}$ between 1 and 2 mm over the 0.6 \textless B$_{\mathrm{pol}}$ \textless 1.0T range. However, we also measure widths that are significantly larger, both within a single discharge and between discharges that are nominally similar. We will continue to search for ``hidden'' variables that might lead to the scatter of the widths above the observed minimum.