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

Experiments were performed on Alcator C-Mod with electron cyclotron resonance (ECR) plasmas to help determine their applicabilty 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 (n(e) approximate to 10(16) m(-3)) outside the resonance location. Electron temperature remained mostly constant outside the resonance location, T-e approximate to 10 eV; ion temperature increased outside the resonance location from T-i approximate to 2 eV to 10 eV. 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/h 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 approximate to 10(-3)) to be lower than other published results for chemical sputtering of deuterium ions on carbon, possibly due to toroidally asymmetric plasma conditions. (C) 1999 Elsevier Science B.V. All rights reserved.