Modeling of energetic particle transport in optimized stellarators

Abstract

Nine stellarator configurations, three quasiaxisymmetric, three quasihelically symmetric and three non-quasisymmetric are scaled to ARIES-CS size and analyzed for energetic particle content. The best performing configurations with regard to energetic particle confinement also perform the best on the neoclassical Γc metric, which attempts to align contours of the second adiabatic invariant with flux surfaces. Quasisymmetric configurations that simultaneously perform well on Γc and quasisymmetry have the best overall confinement, with collisional losses under 3%, approaching the performance of ITER with ferritic inserts.

Direct computation of magnetic surfaces in Boozer coordinates and coil optimization for quasisymmetry

“…We note that this imperfect correlation between quasisymmetry and energetic particle confinement is consistent with the findings in Bader et al. (2021), and in Landreman & Paul (2022) where the QA+Well configuration had lower particle losses than the QA configuration despite worse quasisymmetry. For (Nemov et al.…”

“…For the longer QA-III[22] and QA-III[24] coils, the (small) particle losses are comparable to those for QA-II[22] and QA-II[24], respectively, despite significantly better quasisymmetry throughout the volume. We note that this imperfect correlation between quasisymmetry and energetic particle confinement is consistent with the findings in Bader et al (2021), and in Landreman & Paul (2022) where the QA+Well configuration had lower particle losses than the QA configuration despite worse quasisymmetry. For 3/2 eff (Nemov et al 1999) we observe significant improvement compared with the coils of Wechsung et al (2022b), and our procedure is even able to improve the results from the target field of Landreman & Paul (2022).…”

Optimization of quasisymmetric stellarators with self-consistent bootstrap current and energetic particle confinement

“…This chart displays the fraction of alpha particle energy that is lost for a variety of stellarator configurations, using calculations similar to the recent study in Ref. 36. Each configuration has been scaled to the minor radius and averaged field strength of ARIES-CS.…”

Divertor leg control of a quasi‐symmetry stellarator with external coils and its consequences for transport

“…Although the heliotron‐type device, the Large Helical Device (LHD), [ 4 ] was designed apart from the quasi‐symmetry concept, improvement of energetic particle confinement was obtained with its inward‐shifted configuration, comparable to quasi‐symmetry configurations. [ 5 ] One of the distinct advantages of the LHD configuration is the inherent and robust formation of the divertor legs and the long distance between the core plasma and the plasma‐facing walls. That is a missing feature in design studies of quasi‐symmetry stellarator devices designed with toroidally separated modular coils.…”