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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.

A motional Stark effect (MSE) instrument to measure q(r) using the Torus Experiment for Technology (TEXT) neutral beam on the Alcator C-Mod tokamak has been designed and installed. The neutral beam is on the midplane, aimed radially, and designed to operate in hydrogen at 50 keV. The MSE optics view the outer half of the plasma −0.3

An eight-channel beam-emission-spectroscopy (BES)1 system has been installed on the Alcator C-Mod tokamak, intended for use with a diagnostic neutral hydrogen beam (DNB). Capable of localized measurements from the plasma edge to the plasma core, the BES diagnostic collects light from the first Balmer transition (Hα) resultant from beam/plasma collisions. The Hα line splits into several components whose central wavelengths depend on the viewing geometry, the magnetic field, and the beam energy. This is due to the Doppler shifts from viewing the beam off perpendicular, the different velocities of the three mass components of the beam (H, H2, H3), and the large motional Stark effect. Optimal signal-to-noise requires collecting these components while attenuating all other emission: primarily bremsstrahlung and Dα radiation (from plasma D0/e− collisions). Tunable bandpass filters are thus required. A BES simulation code has been developed that calculates the brightnesses (bremsstrahlung, Dα, Hα) versus wavelen...