Laser-induced fluorescence of helium ions in ITER divertor.

• The laser-induced fluorescence diagnostic system for measuring the ITER divertor plasma parameters is described. • The LIF spectroscopic schemes and lasers are chosen for measurements of HeII density and temperature. • The LIF and background signals and the relative accuracies are calculated for both He and DT discharges of ITER. Laser-induced fluorescence (LIF) on ITER will be used for local measurement of helium density n He and ion temperature T i in divertor. The LIF diagnostic is combined with the divertor Thomson scattering (DTS) via common laser injection and signal collection optics. Collisional-radiative model developed for helium ions is used to estimate laser parameters required for robust measurement of laser-induced signals against plasma background radiation. The estimations demonstrate feasibility of measuring n HeII with laser parameters provided by available optical parametric oscillator pumped by Nd:YAG. New approach for measuring T i is proposed and the expected errors are estimated using numerical simulations. [ABSTRACT FROM AUTHOR]