Determination of atomic hydrogen density and fluorescence decay time by 1D resolved, picosecond TALIF in the RAID linear device

We report on the first 1D resolved two-photon absorption laser-induced fluorescence (TALIF) measurements of atomic hydrogen (H) performed in the Resonant Antenna Ion Device using a picosecond laser system. The results are obtained across a cylindrical plasma column with peak electron density 10 18 m − 3 and temperature 1 eV on axis, which decrease monotonically to 2 ⋅ 10 17 m − 3 and 0.75 eV over a scale of a few cm away from the axis. TALIF results in these conditions are compatible with a uniform H density profile across the observed region, with a mean dissociation degree close to 3%. The small variation of H density across regions covering a wide range of plasma parameters suggests that transport processes and wall interactions play an important role in determining the H density profile. The fluorescence decay time is close to 10 ns at all observed locations, a result compatible with complete substate mixing of the n = 3 states of H.