Interpretation of neutral beam emission spectra as the beam-component density distribution

Diagnostic neutral beams (DNBs) are used on tokamaks and stellarators for measurement of ion temperature, plasma current density, and other critical quantities. It is important to optimize the density in the energy components of the DNB for the diagnostic application. Measured component densities are also useful for interpretation of beam diagnostics and for design of new diagnostics. The spectrally resolved photon emission from the interaction of the neutral beam with a background neutral gas is commonly used for this measurement. The emission cross sections available for interpretation of the measurement are reviewed here. Simulations employ these cross sections with other data to infer the properties of the plasma sources from which the beams are extracted. The simulations are also reviewed. Empirical examples are drawn from beam emission spectra measured for beams installed at the Alcator C-Mod facility