Abstract Details
Abstracts
Author: Silvia Trinczek
Requested Type: Poster
Submitted: 2025-03-13 11:02:06
Co-authors: F.I.Parra, P.J.Catto, I.Calvo
Contact Info:
Princeton Plasma Physics Laboratory
100 Stellarator Rd
Princeton, 08540
United States
Abstract Text:
Strong gradient regions in tokamaks such as the pedestal or internal transport barriers are regions of reduced turbulence where neoclassical transport can play a dominant role. However, standard neoclassical transport theory assumes that the gradient length scales of density, temperature and potential are of the order of the system size. In the pedestal, gradient length scales of the order of the ion poloidal gyroradius have been measured [1]. Standard neoclassical theory misses out on important strong gradient effects where neoclassical transport is a relevant transport mechanism due to suppressed turbulence.
We aim to extend neoclassical theory into regions of gradients of the order of the ion poloidal gyroradius to capture strong gradient effects on transport processes in the pedestal and internal transport barriers. The fundamental idea behind this new framework is to keep a scale separation between the orbit widths and the gradient length scales by performing a large aspect ratio expansion. In the plateau regime, this requires an expansion in both the smallness of the collisional layer and in the smallness of the mirror force term. Following the procedure in [2], we find the discontinuous jump of the distribution function across the collisional layer from which we can derive the neoclassical transport equations.
In the plateau regime, strong gradients cause poloidal variation that is in-out, as well as up-down asymmetric. We study two different test cases assuming either the absence of turbulence or radial force balance and show that strong gradient effects modify standard neoclassical theory predictions in the plateau regime in strong gradient regions.
[1] Viezzer et al. "High-accuracy characterization of the edge radial electric field at ASDEX Upgrade." Nuclear Fusion 53.5 (2013): 053005
[2] Trinczek et al. "Neoclassical transport in strong gradient regions of large aspect ratio tokamaks." Journal of Plasma Physics 89.3 (2023): 905890304
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