TALIF of atomic hydrogen in the divertor simulator NAGDIS-T

Reducing the heat load on the divertor by plasma detachment is essential for the establishment of a fusion reactor, and atomic and molecular processes involving neutral particles are important for understanding and controlling such processes. The ground states and metastable atoms which have long lifetimes are considered to play an important role in the divertor region. However, detailed measurements have not yet been fully implemented in the divertor environment. In the detached plasmas, where plasma recombination can dominate the processes, passive spectroscopy cannot be applied to measure the ground state densities. In this study, we measure hydrogen (H) atomic density by two photon absorption laser induced fuluorescense (TALIF). A dye laser (LIOPTEC, LIOPStar) pumped by a second harmonic of the YAG laser is used for the TALIF. The third harmonic of 615 nm (205 nm) is used to excite H atoms (n=1→3, 205 nm×2 photons) and detect the emission at 656 nm. The H signals were detected using a photomultiplier tube in the divertor simulator NAGDIS-T, where H plasmas can be produced in steady state using DC arc discharge. Also, for the density calibration, we introduced krypton (Kr) gas to the chamber and measured Kr TALIF signal.