Description
A high-resolution main ion charge exchange recombination spectroscopy system has been used to characterize the deuterium temperature at the edge of H-mode plasmas in the ASDEX Upgrade tokamak, enabling new advances in edge physics and heat transport studies [1]. Both main ion (TD) and impurity (Tz) temperatures have been measured, revealing temperature differences up to 80 eV, with TD>TZ. These findings, identified at the pedestal top in cases with higher ECRH power, challenge the conventional assumption of TD=TZ due to strong ion collisional coupling [2].
To interpret these observations, the flexibility of the ASTRA code [3] has been exploited, as it allows for independent implementation of the main ion and impurity heat transport equations. Power balance analysis has been carried out to characterize the experimental deuterium and impurity heat conductivities, revealing a significantly higher χz/χD ratio when TD>TZ.
The properties of χz/χD have been explored using gyrofluid (TGLF) [4] and gyrokinetic (GKW) models [5], showing that χz/χD depends on the ion to the electron heat flux (Qi/Qe), in agreement with analytical theory [6]. The compatibility of the theoretical results with the experimental observations have been tested via predictive modeling with ASTRA. The predictive simulations successfully reproduce a temperature difference of 60 eV, consistent with experimental results, providing first-of-a-kind validation of multi-ion heat transport physics at the plasma edge [2].
[1] P. Cano-Megias et al 2019 J. Instrum. 14 C10040
[2] P. Cano-Megias et al 2025 Nucl. Fusion 65 096027
[3] G.V. Pereverzev and P.N. Yushmanov 2002. Automated system for transport analysis. Technical Report (Max-Planck-Institut für Plasmaphysik)
[4] G. Staebler et al 2024 Nucl. Fusion 64 103001
[5] A.G. Peeters et al 2009 Comput. Phys. Commun. 180 2650–72
[6] C. Angioni, 2015 Phys. Plasmas 22, 102501