Beam spectroscopy for Fast Magnetic Field and Plasma Rotation Measurements within the Pedestal at DIII-D

A set of two newly designed, single-channel Czerny-Turner spectrometers [1/2] has been deployed at the DIII-D tokamak for simultaneous and co-located measurements of the full Motional Stark Effect (MSE) Split Deuterium or Hydrogen Beam Emission and the Carbon CVI charge exchange emission at high spectral (∆λ=0.13 nm) and temporal resolution (1-5 kHz). High throughput optics (f/#=2.8) allow for good signal-to-noise at high time resolution using fast EMCCD detectors. The MSE emission allows for spectral fitting of the magnitude and direction of the local B-field, while the Carbon emission yields local ion temperature and toroidal rotation information. At the light collection lens system at DIII-D, a new channel-specific variable lens-masking approach has been developed and shown to reduce the doppler broadening effect for the MSE emission. Experimental data has been collected from the 2023 and 2024 DIII-D experimental campaigns, focusing on measurements of fast changes in the magnetic field structure due to modifications of the bootstrap current – as well as rotation changes – in the plasma pedestal region (spatial resolution≈0.5 cm) during the ELM cycle and other events. Initial results resolving the evolution of the toroidal rotation and magnetic field fits will be presented, along with initial non-equilibrium beam population modeling and analysis via the code NOMAD.