Comparison of Langmuir probe and Thomson scattering measurements in DIII-D

In this paper, we compare measurements of density and electron temperature made by target plate Langmuir probes (LP) and the divertor Thomson scattering (DTS) diagnostics in the DIII-D tokamak divertor. By examining low-density, ohmic ELM-free discharges, we can use the simple standard electron thermal conduction model (SETC) to relate the measurements at different but closely spaced locations. For this nearly sheath-limited regime, we have derived a correction factor of ∼0.8 for local LP temperature values based on the SETC model. We have sorted the DTS measurements above the plate onto flux surfaces, calculated the connection length to the plate, and constructed parallel density and temperature profiles for comparisons along the magnetic field lines. Measurements from both diagnostics are consistent with the predictions of this very simple model.