Accuracies of motional Stark effect measurements under multiple-ion-source neutral beam injection

The motional Stark effect (MSE) diagnostic in the KSTAR tokamak has been operational along with the neutral beam injection composed of three ion sources. Operating such a beam system imposes constraints on the beam energy deployment as well as on MSE measurements due to the beam emission spectral overlaps. Previous efforts to identify this effect include a simple Stokes vector model and a numerical optimization based on measured intensities of polarized light before and after the beam overlap. Advanced from these previous efforts, a model has been extended to cover a wide range of neutral beam energies and a scenario where the main MSE signal source is switched to a different beam ion source. The model also includes the distortion of band-pass filter transmission functions, beam energy fractional components, and reference pitch angle profiles obtained from the MSE measurements on KSTAR discharges during an entire campaign. The parameter space of two beam ion source energies on the expected systematic pitch angle offset has been generated to provide precise and quantitative guidelines on neutral beam operations where good MSE measurements are necessary.