Divertor plasma characterization using Langmuir probes in DIII-D

We report here measurements of the divertor electron density and temperature profiles for ohmic, NBI heated L-mode, and H-mode discharges in DIII-D. The scaling of peak divertor plasma parameters with discharge current, line average density, and input power has also been obtained. The measurements were made using two fixed, single-tipped Langmuir probes mounted at the outboard (larger major radius) divertor strike point. Complete profile information is obtained by scanning the separatrix intercept across the probes on either a shot-by-shot basis, or during a single discharge. Electron temperatures as high as 50 eV have been observed during the L-mode; densities are in the range of a few times 10 13 cm 3 . Large negative floating potentials, on the order of kT e , have been observed at the strike point. The temperature and density profiles peak inside the magnetically determined strike point location for L- and H-mode and are more peaked during H-mode, consistent with the improvement in radial transport.