Design and conceptual modeling of a tokamak-like X-point divertor for the Helios quasi-axisymmetric stellarator
4 affiliations
- 1Thea Energy, Inc., 1 Eastern Road, Ste. 3-04, Kearny, 07032, NJ, USA
- 2Columbia University, New York, NY, 10027, USA
- 3Princeton University, Princeton, NJ, 08544, USA
- 4Stanford University, Stanford, CA, 94305, USA
Abstract
A novel divertor solution is presented for a pre-conceptual design point of the quasi-axisymmetric stellarator power plant, “Helios.” This solution, isomorphic to the poloidal divertor in a tokamak, features a toroidally-continuous n=0, m=2 double null configuration in which the X-points do not poloidally link the plasma. This results in a non-resonant divertor geometry which relies on neither low-order resonances nor a chaotic boundary region and which features parallel connection lengths similar to those in tokamaks. When reconstructed with a finite-build planar coilset, the configuration resembles that of a tokamak with resonant magnetic perturbations (“RMPs”) applied. Field line tracing and simplified analytic models are used to justify the assumption of tokamak-like Scrape-off Layer (“SOL”) transport and access to a high-recycling regime in such a configuration. Due to this, it is also speculated that high neutral compression akin to a tokamak will be achievable in such a configuration. Preliminary target geometries for this configuration are introduced. Even without globally optimized target geometries, peak heat flux remains below engineering limits for a reference case at similar radiated power fraction as achievable in existing machines ( f r a d = 90 % ) for a baseline P f u s = 958 MW scenario and only slightly exceeds engineering limits for a conservative, low wetted area case. Initial results indicating resilience of the X-point to pressure profile changes are shown. Lastly, preliminary feasibility studies of a disconnected double null configuration are explored, potentially enabling an engineering-simplified design with only lower targets.
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BibTeX
@article{flom2026design,
title = {{Design and conceptual modeling of a tokamak-like X-point divertor for the Helios quasi-axisymmetric stellarator}},
author = {E.R. Flom and W.B. Kalb and Shreyas Seethalla and C. P. S. Swanson and Ryan Wu and M. Avida and A.H. Doudna Cate and Daniel W. Dudt and Thomas Krüger and Santhosh T. A. Kumar and N. Maitra and D. Gates},
journal = {Fusion Engineering and Design},
year = {2026},
month = jun,
doi = {10.1016/j.fusengdes.2026.115846},
url = {https://doi.org/10.1016/j.fusengdes.2026.115846},
note = {CC BY},
}
RIS
TY - JOUR
TI - Design and conceptual modeling of a tokamak-like X-point divertor for the Helios quasi-axisymmetric stellarator
AU - E.R. Flom
AU - W.B. Kalb
AU - Shreyas Seethalla
AU - C. P. S. Swanson
AU - Ryan Wu
AU - M. Avida
AU - A.H. Doudna Cate
AU - Daniel W. Dudt
AU - Thomas Krüger
AU - Santhosh T. A. Kumar
AU - N. Maitra
AU - D. Gates
PY - 2026
DA - 2026/06/05
JO - Fusion Engineering and Design
DO - 10.1016/j.fusengdes.2026.115846
UR - https://doi.org/10.1016/j.fusengdes.2026.115846
AB - A novel divertor solution is presented for a pre-conceptual design point of the quasi-axisymmetric stellarator power plant, “Helios.” This solution, isomorphic to the poloidal divertor in a tokamak, features a toroidally-continuous n=0, m=2 double null configuration in which the X-points do not poloidally link the plasma. This results in a non-resonant divertor geometry which relies on neither low-order resonances nor a chaotic boundary region and which features parallel connection lengths similar to those in tokamaks. When reconstructed with a finite-build planar coilset, the configuration resembles that of a tokamak with resonant magnetic perturbations (“RMPs”) applied. Field line tracing and simplified analytic models are used to justify the assumption of tokamak-like Scrape-off Layer (“SOL”) transport and access to a high-recycling regime in such a configuration. Due to this, it is also speculated that high neutral compression akin to a tokamak will be achievable in such a configuration. Preliminary target geometries for this configuration are introduced. Even without globally optimized target geometries, peak heat flux remains below engineering limits for a reference case at similar radiated power fraction as achievable in existing machines ( f r a d = 90 % ) for a baseline P f u s = 958 MW scenario and only slightly exceeds engineering limits for a conservative, low wetted area case. Initial results indicating resilience of the X-point to pressure profile changes are shown. Lastly, preliminary feasibility studies of a disconnected double null configuration are explored, potentially enabling an engineering-simplified design with only lower targets.
SN - 0920-3796
SN - 1873-7196
ER -