Diagnostics for the spatial distribution of hydrogen atoms around the divertor region

For measurements of spatial distributions of hydrogen atoms around the divertor region, laser-induced fluorescence (LIF) based on various two-phonon excitation schemes from the ground level is discussed, and merits and demerits under different experimental conditions are compared. Excitation to the n =3 level using an ArF excimer laser (wavelength = 193 nm) and its Raman shifts in deuterium gas (205 and 219 nm) and observation at Balmer alpha transition (656 nm) was found to be the best for the above purpose. A design study of the fluorescence observation and estimation of expected signal to noise (SN) ratios were performed for measurements of atomic hydrogen densities on plasmas around the JFT-2M tokamak divertor, showing that such a measurement is possible.