Tuesday, October 30, 2018
Divertors are crucial to the operation of a future fusion pilot plant as they are the sacrificial 'heat dumps' for plasma heat and particle losses. This is no simple task in present day experiments such as Alcator C-Mod which had record-level parallel heat flux on the order of 1 GW/m^2, and the heat flux is only expected to worsen in future devices. Most divertor heat flux mitigation schemes involve the mitigation of heat flux through radiative losses which lead to an increase in the collisionality in the divertor. However, previous studies on ASDEX Upgrade have reported that increasing divertor collisionality significantly increases heat and particle flux to the side walls in the main chamber which could lead to increased erosion and surface malting of the limiters. However, it is unclear if their results were due to an increase in collisionality of the divertor alone or the entire scrape-off layer. With this in mind, a set of experiments were performed in Alcator C-Mod during the 2016 campaign to attempt to better understand the impact of divertor conditions on scrape-off layer transport. Preliminary experimental and simulation results indicate that a combination of the closed divertor geometry in Alcator C-Mod, and magnetic shear enhanced polarization currents near the X-point effectively isolate divertor conditions from the main chamber and suggest a possible pathway forward.