Speaker
Description
Plasma-wall interactions (PWI) are crucial in determining the overall performance and life-time of tokamak plasma-facing components (PFCs), particularly in high-performance machines like ITER and future fusion reactors. PWIs can lead to erosion, impurity generation, and fuel retention, negatively affecting plasma confinement and integrity of PFCs. Linear plasma devices, such as GyM [1] and its upgraded version BiGyM (expected operational in 2026), are essential testbeds for investigating PWI under controlled and cost-effective conditions, enabling achievement of ITER-relevant fluences. In this context, modeling tools are required to support the interpretation of experimental data and to establish predictive capabilities for PWI processes.
This work focuses on the application of erosion and impurity-transport Monte Carlo code ERO2.0 [2] to GyM for interpretative analysis, and to BiGyM for predictive studies.
ERO2.0 is used to support the evaluation of the S/XB spectroscopic parameter for tungsten (W), during argon (Ar) plasma discharges in GyM. The S/XB parameter plays a key role in PWIs, as it allows the determination of the erosion flux from photon flux emitted by sputtered particles, measured via optical emission spectroscopy. At low electron densities (<1e17 m-3) and temperatures (<10 eV) as in GyM, accurately estimating the fraction of W atoms leaving the plasma without being ionized—referred to as geometric loss flux (GLF)—not contributing to the S/XB value, is fundamental [3]. Plasma background used as input for ERO2.0 was provided by the SOLPS-ITER code. The simulations were performed using electron impact ionization rate coefficients calculated from Steinbrink’s formula [4], which is better suited for the low-density, cold Ar plasma of GyM, instead of the default values from the ADAS database. ERO2.0 GLF was compared with the value from a simpler analytical model based on the W atom ionization mean free path due to electron collisions. Both approaches agree within a few percent, showing that the GLF accounts for over 90% of the total W flux.
The study will be extended to BiGyM plasma, expected to feature similar temperatures, but densities at least two orders of magnitude higher. Results will be presented at the conference.
[1] A. Uccello, et al., Front. Phys. 11, 1108175 (2023)
[2] J. Romazanov, et. al., IAEA FEC (2021)
[3] A. Cremona, et al., Nucl. Mater. Energy 17, 253 (2018)
[4] T. Schlummer, et. al., Phys. Scr. 2017, 014075 (2017)