ECE electron temperature mapping errors in high-performance DIII-D discharges

The proper mapping of diagnostic profiles to equilibrium flux surfaces is an important step in the analysis of tokamak data. On DIII-D, the mapping of electron temperature profiles obtained from second- and third-harmonic electron cyclotron emission (ECE) occasionally conflicts with that of T e profiles obtained by Thomson scattering, especially in high-performance negative central shear (NCS) discharges. Particularly, the ECE diagnostics report higher electron temperatures than the Thomson scattering measurements on the low-field side, although the profiles coincide within the measurement uncertainties on the high-field side. It is believed that this is the result of errors in the mapping of ∣ B∣ to ρ, the normalized minor radius. This problem can be characterized for a particular equilibrium by calculating the percent reduction in ∣ B∣ required to force agreement between the ECE and Thomson profiles. Calculations taking relativistic line broadening into account show that the required reduction in ∣ B∣ in the range 0.2< ρ