Evaluation of the main ion flow and temperature using the GPI system GOAL: Direct measurement of the main ion velocity and temperature. Would allow us to verify the assumption that impurities are thermally equilibrated with main ions. Would allow an independent measure of Ti, vtor the latter different from vtor of impurity ions. Usual densities and temperatures on Alcator C-Mod provide generally favorable conditions for performing this measurement. GPI neutrals are cold and their contribution to the spectra should be able to be resolved from the main ion emission. Similar measurement with poloidal and toroidal DNB views may be possible, but we predict it will be more difficult to resolve the signal of interest from the beam neutral emissions.

Main Ion CXRS on DIII-D Temperature measurements of impurities and main ion species (D I) are well correlated into the core among a variety of measurements Courtesy D. Whyte Toroidal velocity measurements vary between impurity and main ion species. Electric field (not shown) inferred from various species similar.

Needs We will use the GPI to stimulate and measure the emission from main ions at the inner wall. Hα will be measured in 2nd order to improve spectral resolution. Radial resolution will be limited by the mean free path of the newly-born hot neutrals. Further into the core would provide better localization, but limited by gas puff penetration. A dedicated half or full day could be used to characterize the diagnostic. L-mode and H-mode. Vary stored energy. LSN shots for characterization. DN and USN time permitting. Vary puff strength. (Possible to study during other runs.) This diagnostic would ideally piggyback whenever appropriate. Become a standard measurement if successful. Compare with DNB spectroscopy Ti, v at the outer edge.