Ultrafast ion temperature and toroidal velocity fluctuation spectroscopy diagnostic design

High sensitivity measurements of localized, long-wavelength ion temperature, and toroidal velocity fluctuations (T(i)/T(i),v(parallel)/v(parallel)) 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 lambda(0)=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 mm(2) sr, two orders of magnitude larger than conventional charge exchange system. The diagnostic will achieve a turbulence-relevant time resolution of 1 micros. System modeling demonstrates a sensitivity of T(i)/T(i) < or = 1%.