Sensitivity of a low-shear heliotron configuration to localised ferrite-steel perturbations
Abstract
The influence of ferritic steel on low-shear stellarator/heliotron magnetic configurations is investigated for the Heliotron J device using a point dipole magnetisation model. By numerically evaluating ferritic steel plates assumed at several locations inside the Heliotron J vacuum vessel, the changes in the rotational transform and magnetic island width are shown to be sensitive to the installation location. This location sensitivity arises from the toroidal variation of poloidal mode coupling between the background nonaxisymmetric field and ferritic-steel perturbation, rather than being determined solely by the perturbation amplitude. The resulting mode coupling can enhance the resonant vacuum magnetic perturbation at specific locations. Ferritic steel plates placed on the outer side of a straight section produce the most significant changes in the magnetic topology and exhibit the highest sensitivity to violations of the M=4 toroidal periodicity. Additionally, we show that appropriate arrangements of passive magnetic dipoles can reduce the effective helical ripple while preserving the vacuum magnetic well depth in Heliotron J, and can induce a stellarator-asymmetric boundary perturbation in low-field experiments.
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BibTeX
@misc{matsuyama2026sensitivity,
title = {{Sensitivity of a low-shear heliotron configuration to localised ferrite-steel perturbations}},
author = {A. Matsuyama and F. Tanji and Y. Nakamura and S. Inagaki and Yusuke Yamashita and Akihisa Yamamoto and S. Kobayashi and F. Kin and S. Kado and S. I. Inagaki and S. Konoshima and T. Mizuuchi and K. Nagasaki},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2607.08290},
eprint = {2607.08290},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2607.08290},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Sensitivity of a low-shear heliotron configuration to localised ferrite-steel perturbations
AU - A. Matsuyama
AU - F. Tanji
AU - Y. Nakamura
AU - S. Inagaki
AU - Yusuke Yamashita
AU - Akihisa Yamamoto
AU - S. Kobayashi
AU - F. Kin
AU - S. Kado
AU - S. I. Inagaki
AU - S. Konoshima
AU - T. Mizuuchi
AU - K. Nagasaki
PY - 2026
DA - 2026/09/17
PB - arXiv
DO - 10.48550/arxiv.2607.08290
UR - https://arxiv.org/abs/2607.08290
AB - The influence of ferritic steel on low-shear stellarator/heliotron magnetic configurations is investigated for the Heliotron J device using a point dipole magnetisation model. By numerically evaluating ferritic steel plates assumed at several locations inside the Heliotron J vacuum vessel, the changes in the rotational transform and magnetic island width are shown to be sensitive to the installation location. This location sensitivity arises from the toroidal variation of poloidal mode coupling between the background nonaxisymmetric field and ferritic-steel perturbation, rather than being determined solely by the perturbation amplitude. The resulting mode coupling can enhance the resonant vacuum magnetic perturbation at specific locations. Ferritic steel plates placed on the outer side of a straight section produce the most significant changes in the magnetic topology and exhibit the highest sensitivity to violations of the M=4 toroidal periodicity. Additionally, we show that appropriate arrangements of passive magnetic dipoles can reduce the effective helical ripple while preserving the vacuum magnetic well depth in Heliotron J, and can induce a stellarator-asymmetric boundary perturbation in low-field experiments.
ER -