Synthetic motional Stark effect diagnostics with a radial electric field*

A forward model has been developed to retrieve synthetic data for motional Stark effect (MSE) diagnostics in the KSTAR tokamak. Starting with reference pitch angle profiles, inverse application of the mapping calibration establishes Stokes vectors in the demodulated signals. Another inversion against the photo-elastic modulator retrieves the input Stokes vectors and corresponding modulated raw signals. With the help of the neutral beam penetration calculations, the full MSE spectra with polarization information are reconstructed. Key features include the consideration of an intrinsic radial electric field which is regarded as one of the main mechanisms to suppress turbulences. In diagnostic perspective, however, it may act as a source of systematic errors in the MSE diagnostics. A dual MSE measurement approach is also discussed in the synthetic diagnostic model to correct the radial electric field effect, where the second MSE measurement is made either from the pi or sigma component in the half-energy beam fraction spectra.