Divertor erosion in DIII-D

Net erosion rates of carbon target plates have been measured in situ for th e DIII-D lower divertor. For attached diverters (T-e > 40 eV), outer strike point (OSP) erosion rates exceed 10 cm/exposure-year, physical sputtering is dominant and the effective sputtering yield, Y, is greater than 10%. In detached diverters (T-e < 2 eV), the cold incident plasma eliminates physic al sputtering and net erosion is suppressed at the OSP, which becomes st re gion of net redeposition (similar to 4 cm/exposure-year). Molecular spectro scopy indicates an upper limit of Y less than or equal to 0.1% for the chem ical sputtering yield. The private flux wall is measured to be a region of net redeposition with dense, high neutral pressure, attached divertor plasm as. Leading edges intercepting parallel heat flux (similar to 50 MW/m(2)) h ave very high net erosion rates (similar to 10 mu m/s) at the OSP of an att ached plasma. (C) 1999 Elsevier Science B.V. All rights reserved.