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) cm3. 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.