BEAM EMISSION-SPECTROSCOPY AS A COMPREHENSIVE PLASMA DIAGNOSTIC-TOOL

A beam of injected fast atomic hydrogen presents a superb probe for ho t fusion plasmas. The neutral particles experience excitation and ioni zation by collisions with electrons and ions as they penetrate into a plasma. The emitted characteristic line radiation is Doppler shifted a nd the spectral lines are split due to motional Stark fields. Measurem ents of wavelength, intensity and polarization of the Balmer-alpha emi ssion reveal information about the neutral beam, such as beam attenuat ion, beam-geometry, beam-divergence and species mix. Local pitch angle s and toroidal fields can be derived from the simultaneous measurement of the polarization pattern and the wavelength separation of the Star k multiplet. The implementation and application of beam emission spect roscopy as a quantitative diagnostic tool on the Joint European Torus (JET) experiment is reviewed.