Electron cyclotron discharge cleaning (ECDC) experiments on Alcator C-Mod

Experiments were performed on Alcator C-Mod with Electron Cyclotron resonance plasmas to help determine their applicability to a fusion reactor. Strong radial inhomogeneity of the plasma density was measured, decreasing by a factor of ten a few centimeters inside the resonance location, but remaining approximately constant (ne ∼ 1016 m-3) outside the resonance location. Electron and ion temperatures remained mostly constant outside the resonance location (Τe ∼ 10eV, Τi ∼ 2eV). Toroidal asymmetries in ion saturation current density were observed, indicating local toroidal plasma flow. The ECR plasma was used to remove a diamond-like carbon coating from a stainless-steel sample. Removal rates peaked at 4.2 ± 0.4 nm/hour with the sample a few centimeters outside the resonance location. Removal rates decreased inside and further outside the resonance location. The plasma did not remove the carbon from the sample uniformly, possibly due to plasma flow. Yields were calculated (Y ∼10-3) to be lower than other published results for chemical sputtering of deuterium ions on carbon, possibly due to toroidally asymmetric plasma conditions. Significant redeposition was not observed