Impurity control in a tokamak edge plasma by a method of Doppler-free spectroscopy

The laser-induced fluorescence (LIF) technique is proposed to use for local determination of an effective ionic charge in a plasma edge of large fusion devices. The method is based on non-linear phenomenon of saturation of an optical transition of hydrogen atom excited by means of an intense laser light with a small spectral width. It is demonstrated that measurements of a slight Stark broadening without Doppler-broadened background are possible under conditions typical of tokamak plasma. One of approaches for evaluation of an effective ionic charge from the homogeneous Stark width is discussed in detail.