AbstractThe 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 Te 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<0.8 is less than 5% in almost all cases, and is typically closer to 2%. Since the vacuum B-field is known to within a fraction of a percent, a discrepancy in total B must represent errors involving finite beta or other plasma parameters not related to vacuum magnetic field. The required reduction in ∣B∣ versus various parameters is investigated for a database of shots. It is found that in many cases the overlap error is due to the presence of large magnetic islands associated with locked modes.
Investigation of ion and electron heat transport of high-Te ECH heated discharges in the large helical device
Thomson scattering diagnostic in the boundary layer of ASDEX