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

Experiments were performed on Alcator C-Mod with electron cyclotron resonan ce (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 rem aining approximately constant (n(e) approximate to 10(16) m(-3)) outside th e resonance location. Electron temperature remained mostly constant outside the resonance location, T-e approximate to 10 eV; ion temperature increase d outside the resonance location from T-i approximate to 2 eV to 10 eV. Tor oidal asymmetries in ion saturation current density were observed, indicati ng 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 lo cation. Removal rates decreased inside and further outside the resonance lo cation. The plasma did not remove the carbon from the sample uniformly, pos sibly due to plasma flow. Yields were calculated (Y approximate to 10(-3)) to be lower than other published results for chemical sputtering of deuteri um ions on carbon, possibly due to toroidally asymmetric plasma conditions. (C) 1999 Elsevier Science B.V. All rights reserved.