Femtosecond TALIF for H density measurement in RAID

The role of atomic hydrogen (H) is key to the dynamics of the plasma edge in tokamaks. Measurements of H density in tokamaks are nevertheless mostly indirect, often relying on analyses of optical emission spectroscopy data.



Two-photon-absorption laser-induced fluorescence (TALIF) is an absolutely-calibrated alternative, potentially providing direct and localized measurements of H density [1, 2]. In addition, femtosecond laser pulses (of spectral width ~0.1-1 nm) allow the excitation of H ground-state population independent of any broadening mechanism, opening the way to single-laser-pulse measurements of H density, that may be well adapted to tokamak operations [3].



In this work, we present the development of a single-pulse fs-TALIF system [4] in the linear device RAID [5], in a hydrogen plasma with plasma density ~10¹⁸ m^-3. As part of the development of our fs-TALIF system, measurements of the fluorescence decaytime in RAID are also presented.



[1] L. Kadi et al., Plasma Phys. Control. Fusion 66, 125007 (2024)

[2] R. M. Magee et al., Rev. Sci. Instrum. 83, 10D701 (2012)

[3] A. Dogariu et al., Rev. Sci. Instrum. 93, 093519 (2022)

[4] EUROfusion Enabling Research project ENR-TEC.02.EPFL

[5] R. Jacquier et al., Fusion Eng. Des. 192, 113614 (2023)