Fast-ion D-alpha diagnostic development for the C-2W field-reversed configuration plasma.

TAE Technologies's advanced beam-driven field-reversed configuration device has a large fast-ion population, allowing for fast-ion D-alpha (FIDA) studies. Development of a FIDA spectrometer for the new C-2W device is underway. Previous measurements were combined with C-2W geometry to inform the design [N. Bolte, Rev. Sci. Instrum. 87, 11E520 (2016)]. Measured signal levels led to the purchase of a Phantom Miro 110 high-speed camera that will be paired with a Holospec f/1.8 spectrograph from Kaiser Optical Systems, Inc. The spectrograph utilizes a custom transmission grating centered at 656.0 nm. Simulations were used to choose available ports with large predicted signals. Eight neutral beams and 354 ports were considered. Experimentally obtained 1D plasma profiles from C-2U were mapped onto Q2D [M. Onofri, Phys. Plasmas 24, 092518 (2017)] simulation flux surfaces. For each point on the vessel wall, many lines-of-sight (LOSs) are created to view the entirety of each neutral beam path. FIDA spectra are simulated for each LOS using the FIDA simulation code FIDASIM [http://d3denergetic.github.io/FIDASIM/; W. Heidbrink, Commun. Comput. Phys. 10, 716 (2011); and B. Geiger, "Fast-ion transport studies using FIDA spectroscopy at the ASDEX Upgrade tokamak," Ph.D. thesis, Ludwig Maximilian University of Munich, 2012]. Integrating over wavelength and beam-space allows individual ports to be chosen for their large prospective signals.