An analysis of the attenuation behaviour of neutral beams injected for plasma heating is discussed, which yields a beam deposition profile for a known plasma density profile or which may provide a plasma density profile. The population of surviving beam trals at a penetration depth into a plasma is inferred from the excitation process of the fast neutrals. The excitation light is roughly independent of the electron temperature, and the line spectra can easily be distinguished by means of Dopplershift spectroscopy. Hydrogenic neutral beams typically consist of three energy species (E, E/2,E/3) with different survival probabilities. By comparing the excitation light from each species at several points along the beam path, it is possible to decode information on the plasma density through which the beam has passed. On the other hand, if the plasma density profile is known from other diagnostics, the fast ion deposition profile can be obtained. A preliminary result of single-chord measurements in Doublet III is presented.
Neutral beam probe spectroscopy for the measurement of local plasma density fluctuations