Abstract Details
Abstracts
Author: Julien Dominski
Requested Type: Consider for Invited
Submitted: 2026-03-01 12:29:12
Co-authors: F.I.Parra, T.Adkins, T.Barbui, L.F.Delgado, P.Maget, P. Manas, M.O'Mullane
Contact Info:
Princeton Plasma Physics Laboratory
100 Stellarator rd
Princeton, 08540
USA
Abstract Text:
The influence of the tungsten electric charge state on its turbulent transport and peaking factor is investigated in the collisionless trace-impurity limit, emphasizing how finite Larmor radius (FLR) effects modulate passive turbulent fluxes and density peaking. The analytical estimates of the tungsten peaking factor, derived from the stochastic nature of the field [1], are verified for all ion charge states against nonlinear GX simulations [2].
In the ion-temperature-gradient (ITG) regime, a minimum of the peaking factor appears at intermediate charge states, caused by FLR-induced changes to the $Etimes B$ drift of tungsten density perturbations -- the ``nonlinear $Etimes B$ term''. The existence of such a minimum predicts optimized plasma configurations that are unexpected from a quasi-linear theory or modeling. Indeed quasi-linear estimates, even those using a linear tungsten response in a nonlinear turbulent field, fail to capture this behavior and thus inaccurately describe tungsten turbulent transport and peaking.
This passive response of tungsten is shown to have a strong dependence on the normalized perpendicular wavenumber $k_perp rho$, predicting a large peaking factor for small-scale electron-temperature-gradient (ETG) turbulence. Combined with atomic-physics effects on the Larmor radius, this can significantly alter tungsten penetration into the pedestal.
Similar trends hold for other impurities, such as boron and neon. The results are finally related to the theoretical framework of passive scalar fields in turbulent flows.
[1] G. I. Taylor (1921) “Diffusion by Continuous Movements” Proceedings of the London Mathematical Society, Series 2, Vol. 20, pp. 196–212.
[2] N.R. Mandell et al. (2024), “GX: a GPU-native gyrokinetic turbulence code for tokamak and stellarator design” Journal of Plasma Physics. 2024;90(4):905900402.
Characterization: 1.0
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