Shear Alfvén stability in a quasi-axisymmetric (QA) beam-target stellarator

Thea Energy, Inc. plans to build Eos, a quasi-axisymmetric (QA), large-scale, beam-target fusion, stellarator neutron source. Eos has two oppositely directed neutral beam injectors (NBIs) at toroidal angles 0 and 𝜋. Fast ions from neutral beams can drive Alfvén waves in stellarators, as demonstrated previously in W7-AS [1] and TJ-II [2]. Due to its high-beam-pressure, Alfvénic instabilities are likely important in Eos. A workflow using Stellgap [3], FAR3D [4], and SIMSOPT [5] particle tracing to assess the Alfvénic stability of Eos and beam-driven stellarators in general is presented. Stellgap calculates the Eos shear Alfvén continuum. Comparisons between the gap structure of Eos and other QA configurations are given. FAR3D determines the growth rate and frequency of Alfvén eigenmodes. SIMSOPT particle tracing models the fast particle response to Alfvén eigenmodes. The overall Alfvénic stability analysis presented here for Eos can be applied to other beam-driven stellarators.



[1] A. Weller, et al. Phys. Rev. Lett. 72, 1220–1223 (1994).

[2] A.V. Melnikov, et al. Nucl. Fusion. 54, 123002 (2014).

[3] D. A. Spong, et al. Phys. Plasmas. 10 (8): 3217–3224 (2003).

[4] J. Varela, et al. Front. Phys. 12:1422411 (2024).

[5] M. Landreman, et al. J. Open Source Software. 6, 3525 (2021).