Laser-Aided Plasma Diagnostics

This paper will focus on two types of laser-aided diagnostics: Thomson scattering and laser-induced fluorescence. Thomson scattering is a very powerful diagnostic, which is applied at nearly every magnetic confinement device. Depending on the experimental conditions different plasma parameters can be diagnosed. When the wavelength is much smaller than the plasma Debye length, the total scattered power is obtained by an incoherent summation over the scattered powers of the individual electrons. The scattering spectrum in this case is a reflection of the electron velocity distribution, from which local values for the electron temperature and density can be derived. In case the wavelength is larger than the Debye length, Thomson scattering can yield information on the ion velocity distribution and/or collective behavior of the electrons, as is the case with density fluctuations. Laser-induced fluorescence is particularly suited for studies of the ion population at the cooler, not-fully ionized, plasma edge.