Localized measurements of electron cyclotron current drive using MSE spectroscopy on the DIII-D tokamak

A new method of current drive analysis is demonstrated that compares the me asured pitch angles from motional Stark effect (MSE) spectroscopy with simu lations of the expected MSE response to localized ECCD. By comparing simula tions of the MSE signals with measurements, the best fit of the ECCD profil e is determined. The ECCD efficiency ascertained in this manner decreases a s the current drive location moves to larger minor radius owing to electron trapping effects. The ECCD efficiency is shown to be highest when the driv en current is on the high magnetic field side of the plasma, as expected fr om theory. The width of the ECCD profile is also in good agreement with the ory; previous reports of a broader than expected ECCD profile are shown to have been caused by insufficient radial resolution of the magnetic equilibr ium reconstruction.