Speaker
Description
Accurate spectroscopic diagnostics for tokamak and stellarator divertors rely on collisional–radiative models (CRMs), whose predictive power is often limited by uncertain collisional rates [1]. The Resonant Antenna Ion Device (RAID) at the Swiss Plasma Center provides a controlled, steady-state plasma environment relevant to magnetic confinement fusion that is ideally suited for validating CRMs by classical and advanced spectroscopic techniques.
RAID is a linear device based on helicon excitation that produces stable plasmas in Ar, He, H₂, and D₂ with densities up to a few $10^{18}$ m$^{−3}$ (few $10^{19}$ m$^{−3}$ for He/Ar) and electron temperatures up to 10 eV [2,3], representative of divertor and edge conditions. The device is equipped with a comprehensive set of conventional diagnostics [3], and has recently become a platform for advanced active-spectroscopy development. A TaLIF system for atomic hydrogen density measurement [4] demonstrated its relevance for benchmarking of neutral-transport models like SOLPS-EIRENE [5] and has recently been upgraded for investigations of single-laser-pulse H density measurements, with potential application in tokamaks.
Building on this capability, we have recently implemented a laser-collisional induced fluorescence (LCIF) diagnostic based on a wavelength-tunable picosecond laser system. By selectively overpopulating excited atomic states and tracking the population redistribution, LCIF provides direct, in-situ measurements of collisional rates [6]. These rates, traditionally inferred from simulations or particle-beam experiments, are critical inputs for CRMs used to interpret optical emission spectroscopy (OES) measurements in fusion devices. LCIF measurements on RAID enable validation and refinement of CRMs, particularly in the low-temperature He/H/D regime relevant for tokamak divertors, that was shown to be challenging for CRMs [7].
In this contribution, we will present the LCIF diagnostic and first measurement results on RAID. We will discuss how LCIF, OES, and Thomson scattering measurements on RAID will be used in synergy to validate CRMs to improve spectroscopic diagnostic of tokamak and stellarator divertors.
[1] Flom et al., Nuclear Materials and Energy, Vol. 33, 2022
[2] Furno et al., 22 Topical Conference on Radio-Frequency Power in Plasmas, 2017
[3] Jacquier et al., Fusion Engineering and Design, Vol. 192, 2023
[4] Kadi et al., Plasma Physics and Controlled Fusion, Vol. 66, No. 12, 2024
[5] Kadi, L., Phd Thesis, EPFL, 2025
[6] Denkelmann, et al., Journal of Physics B: Atomic, Molecular and Optical Physics, Vol. 32, No. 19, 1999
[7] Linehan et al., Nuclear Fusion, Vol. 63, No. 3, 2023