Ultrafast ion temperature and toroidal velocity fluctuation spectroscopy diagnostic design

High sensitivity measurements of localized, long-wavelength ion temperature, and toroidal velocity fluctuations (T̃ i / Ti, ṽ / v) are required to address critical issues pertaining to turbulent transport. This diagnostic design exploits emission from charge exchange recombination between neutral beam atoms and the intrinsic carbon impurity. The n=8-7 transition of C VI at λ0 =529.05 nm will be measured. The key difference between this diagnostic design and conventional charge exchange spectrometers is the use of high-efficiency prism-coupled transmission gratings, avalanche photodiode detectors, and high-throughput collection optics. The spectrometer achieves a spectral resolution of 0.25 nm, and observes 528.0-530.0 nm with eight discrete spectral channels, with an entrance throughput of 1.6 mm2 sr, two orders of magnitude larger than conventional charge exchange system. The diagnostic will achieve a turbulence-relevant time resolution of 1 μs. System modeling demonstrates a sensitivity of T̃ i / Ti 1%.